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<h2>Active Record Validations</h2><p>This guide teaches you how to validate the state of objects before they go into
the database using Active Record's validations feature.</p><p>After reading this guide, you will know:</p>
<ul>
<li>How to use the built-in Active Record validation helpers.</li>
<li>How to create your own custom validation methods.</li>
<li>How to work with the error messages generated by the validation process.</li>
</ul>
<div id="subCol">
<h3 class="chapter"><img src="images/chapters_icon.gif" alt="" />Chapters</h3>
<ol class="chapters">
<li>
<a href="#validations-overview">Validations Overview</a>
<ul>
<li><a href="#why-use-validations-questionmark">Why Use Validations?</a></li>
<li><a href="#when-does-validation-happen-questionmark">When Does Validation Happen?</a></li>
<li><a href="#skipping-validations">Skipping Validations</a></li>
<li><a href="#valid-questionmark-and-invalid-questionmark"><code>valid?</code> and <code>invalid?</code></a></li>
<li><a href="#validations-overview-errors"><code>errors[]</code></a></li>
<li><a href="#validations-overview-errors-details"><code>errors.details</code></a></li>
</ul>
</li>
<li>
<a href="#validation-helpers">Validation Helpers</a>
<ul>
<li><a href="#acceptance"><code>acceptance</code></a></li>
<li><a href="#validates-associated"><code>validates_associated</code></a></li>
<li><a href="#confirmation"><code>confirmation</code></a></li>
<li><a href="#exclusion"><code>exclusion</code></a></li>
<li><a href="#format"><code>format</code></a></li>
<li><a href="#inclusion"><code>inclusion</code></a></li>
<li><a href="#length"><code>length</code></a></li>
<li><a href="#numericality"><code>numericality</code></a></li>
<li><a href="#presence"><code>presence</code></a></li>
<li><a href="#absence"><code>absence</code></a></li>
<li><a href="#uniqueness"><code>uniqueness</code></a></li>
<li><a href="#validates-with"><code>validates_with</code></a></li>
<li><a href="#validates-each"><code>validates_each</code></a></li>
</ul>
</li>
<li>
<a href="#common-validation-options">Common Validation Options</a>
<ul>
<li><a href="#allow-nil"><code>:allow_nil</code></a></li>
<li><a href="#allow-blank"><code>:allow_blank</code></a></li>
<li><a href="#message"><code>:message</code></a></li>
<li><a href="#on"><code>:on</code></a></li>
</ul>
</li>
<li><a href="#strict-validations">Strict Validations</a></li>
<li>
<a href="#conditional-validation">Conditional Validation</a>
<ul>
<li><a href="#using-a-symbol-with-if-and-unless">Using a Symbol with <code>:if</code> and <code>:unless</code></a></li>
<li><a href="#using-a-proc-with-if-and-unless">Using a Proc with <code>:if</code> and <code>:unless</code></a></li>
<li><a href="#grouping-conditional-validations">Grouping Conditional validations</a></li>
<li><a href="#combining-validation-conditions">Combining Validation Conditions</a></li>
</ul>
</li>
<li>
<a href="#performing-custom-validations">Performing Custom Validations</a>
<ul>
<li><a href="#custom-validators">Custom Validators</a></li>
<li><a href="#custom-methods">Custom Methods</a></li>
</ul>
</li>
<li>
<a href="#working-with-validation-errors">Working with Validation Errors</a>
<ul>
<li><a href="#working-with-validation-errors-errors"><code>errors</code></a></li>
<li><a href="#errors"><code>errors[]</code></a></li>
<li><a href="#errors-add"><code>errors.add</code></a></li>
<li><a href="#working-with-validation-errors-errors-details"><code>errors.details</code></a></li>
<li><a href="#errors-base"><code>errors[:base]</code></a></li>
<li><a href="#errors-clear"><code>errors.clear</code></a></li>
<li><a href="#errors-size"><code>errors.size</code></a></li>
</ul>
</li>
<li><a href="#displaying-validation-errors-in-views">Displaying Validation Errors in Views</a></li>
</ol>
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<h3 id="validations-overview"><a class="anchorlink" href="#validations-overview">1 Validations Overview</a></h3><p>Here's an example of a very simple validation:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, presence: true
end
Person.create(name: "John Doe").valid? # => true
Person.create(name: nil).valid? # => false
</pre>
</div>
<p>As you can see, our validation lets us know that our <code>Person</code> is not valid
without a <code>name</code> attribute. The second <code>Person</code> will not be persisted to the
database.</p><p>Before we dig into more details, let's talk about how validations fit into the
big picture of your application.</p><h4 id="why-use-validations-questionmark"><a class="anchorlink" href="#why-use-validations-questionmark">1.1 Why Use Validations?</a></h4><p>Validations are used to ensure that only valid data is saved into your
database. For example, it may be important to your application to ensure that
every user provides a valid email address and mailing address. Model-level
validations are the best way to ensure that only valid data is saved into your
database. They are database agnostic, cannot be bypassed by end users, and are
convenient to test and maintain. Rails makes them easy to use, provides
built-in helpers for common needs, and allows you to create your own validation
methods as well.</p><p>There are several other ways to validate data before it is saved into your
database, including native database constraints, client-side validations and
controller-level validations. Here's a summary of the pros and cons:</p>
<ul>
<li>Database constraints and/or stored procedures make the validation mechanisms
database-dependent and can make testing and maintenance more difficult.
However, if your database is used by other applications, it may be a good
idea to use some constraints at the database level. Additionally,
database-level validations can safely handle some things (such as uniqueness
in heavily-used tables) that can be difficult to implement otherwise.</li>
<li>Client-side validations can be useful, but are generally unreliable if used
alone. If they are implemented using JavaScript, they may be bypassed if
JavaScript is turned off in the user's browser. However, if combined with
other techniques, client-side validation can be a convenient way to provide
users with immediate feedback as they use your site.</li>
<li>Controller-level validations can be tempting to use, but often become
unwieldy and difficult to test and maintain. Whenever possible, it's a good
idea to keep your controllers skinny, as it will make your application a
pleasure to work with in the long run.</li>
</ul>
<p>Choose these in certain, specific cases. It's the opinion of the Rails team
that model-level validations are the most appropriate in most circumstances.</p><h4 id="when-does-validation-happen-questionmark"><a class="anchorlink" href="#when-does-validation-happen-questionmark">1.2 When Does Validation Happen?</a></h4><p>There are two kinds of Active Record objects: those that correspond to a row
inside your database and those that do not. When you create a fresh object, for
example using the <code>new</code> method, that object does not belong to the database
yet. Once you call <code>save</code> upon that object it will be saved into the
appropriate database table. Active Record uses the <code>new_record?</code> instance
method to determine whether an object is already in the database or not.
Consider the following simple Active Record class:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
end
</pre>
</div>
<p>We can see how it works by looking at some <code>rails console</code> output:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
$ rails console
>> p = Person.new(name: "John Doe")
=> #<Person id: nil, name: "John Doe", created_at: nil, updated_at: nil>
>> p.new_record?
=> true
>> p.save
=> true
>> p.new_record?
=> false
</pre>
</div>
<p>Creating and saving a new record will send an SQL <code>INSERT</code> operation to the
database. Updating an existing record will send an SQL <code>UPDATE</code> operation
instead. Validations are typically run before these commands are sent to the
database. If any validations fail, the object will be marked as invalid and
Active Record will not perform the <code>INSERT</code> or <code>UPDATE</code> operation. This avoids
storing an invalid object in the database. You can choose to have specific
validations run when an object is created, saved, or updated.</p><div class="warning"><p>There are many ways to change the state of an object in the database.
Some methods will trigger validations, but some will not. This means that it's
possible to save an object in the database in an invalid state if you aren't
careful.</p></div><p>The following methods trigger validations, and will save the object to the
database only if the object is valid:</p>
<ul>
<li><code>create</code></li>
<li><code>create!</code></li>
<li><code>save</code></li>
<li><code>save!</code></li>
<li><code>update</code></li>
<li><code>update!</code></li>
</ul>
<p>The bang versions (e.g. <code>save!</code>) raise an exception if the record is invalid.
The non-bang versions don't: <code>save</code> and <code>update</code> return <code>false</code>, and
<code>create</code> just returns the object.</p><h4 id="skipping-validations"><a class="anchorlink" href="#skipping-validations">1.3 Skipping Validations</a></h4><p>The following methods skip validations, and will save the object to the
database regardless of its validity. They should be used with caution.</p>
<ul>
<li><code>decrement!</code></li>
<li><code>decrement_counter</code></li>
<li><code>increment!</code></li>
<li><code>increment_counter</code></li>
<li><code>toggle!</code></li>
<li><code>touch</code></li>
<li><code>update_all</code></li>
<li><code>update_attribute</code></li>
<li><code>update_column</code></li>
<li><code>update_columns</code></li>
<li><code>update_counters</code></li>
</ul>
<p>Note that <code>save</code> also has the ability to skip validations if passed <code>validate:
false</code> as an argument. This technique should be used with caution.</p>
<ul>
<li><code>save(validate: false)</code></li>
</ul>
<h4 id="valid-questionmark-and-invalid-questionmark"><a class="anchorlink" href="#valid-questionmark-and-invalid-questionmark">1.4 <code>valid?</code> and <code>invalid?</code></a></h4><p>Before saving an Active Record object, Rails runs your validations.
If these validations produce any errors, Rails does not save the object.</p><p>You can also run these validations on your own. <code>valid?</code> triggers your validations
and returns true if no errors were found in the object, and false otherwise.
As you saw above:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, presence: true
end
Person.create(name: "John Doe").valid? # => true
Person.create(name: nil).valid? # => false
</pre>
</div>
<p>After Active Record has performed validations, any errors found can be accessed
through the <code>errors.messages</code> instance method, which returns a collection of errors.
By definition, an object is valid if this collection is empty after running
validations.</p><p>Note that an object instantiated with <code>new</code> will not report errors
even if it's technically invalid, because validations are automatically run
only when the object is saved, such as with the <code>create</code> or <code>save</code> methods.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, presence: true
end
>> p = Person.new
# => #<Person id: nil, name: nil>
>> p.errors.messages
# => {}
>> p.valid?
# => false
>> p.errors.messages
# => {name:["can't be blank"]}
>> p = Person.create
# => #<Person id: nil, name: nil>
>> p.errors.messages
# => {name:["can't be blank"]}
>> p.save
# => false
>> p.save!
# => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank
>> Person.create!
# => ActiveRecord::RecordInvalid: Validation failed: Name can't be blank
</pre>
</div>
<p><code>invalid?</code> is simply the inverse of <code>valid?</code>. It triggers your validations,
returning true if any errors were found in the object, and false otherwise.</p><h4 id="validations-overview-errors"><a class="anchorlink" href="#validations-overview-errors">1.5 <code>errors[]</code></a></h4><p>To verify whether or not a particular attribute of an object is valid, you can
use <code>errors[:attribute]</code>. It returns an array of all the errors for
<code>:attribute</code>. If there are no errors on the specified attribute, an empty array
is returned.</p><p>This method is only useful <em>after</em> validations have been run, because it only
inspects the errors collection and does not trigger validations itself. It's
different from the <code>ActiveRecord::Base#invalid?</code> method explained above because
it doesn't verify the validity of the object as a whole. It only checks to see
whether there are errors found on an individual attribute of the object.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, presence: true
end
>> Person.new.errors[:name].any? # => false
>> Person.create.errors[:name].any? # => true
</pre>
</div>
<p>We'll cover validation errors in greater depth in the <a href="#working-with-validation-errors">Working with Validation
Errors</a> section.</p><h4 id="validations-overview-errors-details"><a class="anchorlink" href="#validations-overview-errors-details">1.6 <code>errors.details</code></a></h4><p>To check which validations failed on an invalid attribute, you can use
<code>errors.details[:attribute]</code>. It returns an array of hashes with an <code>:error</code>
key to get the symbol of the validator:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, presence: true
end
>> person = Person.new
>> person.valid?
>> person.errors.details[:name] # => [{error: :blank}]
</pre>
</div>
<p>Using <code>details</code> with custom validators is covered in the <a href="#working-with-validation-errors">Working with
Validation Errors</a> section.</p><h3 id="validation-helpers"><a class="anchorlink" href="#validation-helpers">2 Validation Helpers</a></h3><p>Active Record offers many pre-defined validation helpers that you can use
directly inside your class definitions. These helpers provide common validation
rules. Every time a validation fails, an error message is added to the object's
<code>errors</code> collection, and this message is associated with the attribute being
validated.</p><p>Each helper accepts an arbitrary number of attribute names, so with a single
line of code you can add the same kind of validation to several attributes.</p><p>All of them accept the <code>:on</code> and <code>:message</code> options, which define when the
validation should be run and what message should be added to the <code>errors</code>
collection if it fails, respectively. The <code>:on</code> option takes one of the values
<code>:create</code> or <code>:update</code>. There is a default error
message for each one of the validation helpers. These messages are used when
the <code>:message</code> option isn't specified. Let's take a look at each one of the
available helpers.</p><h4 id="acceptance"><a class="anchorlink" href="#acceptance">2.1 <code>acceptance</code></a></h4><p>This method validates that a checkbox on the user interface was checked when a
form was submitted. This is typically used when the user needs to agree to your
application's terms of service, confirm that some text is read, or any similar
concept.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :terms_of_service, acceptance: true
end
</pre>
</div>
<p>This check is performed only if <code>terms_of_service</code> is not <code>nil</code>.
The default error message for this helper is <em>"must be accepted"</em>.
You can also pass custom message via the <code>message</code> option.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :terms_of_service, acceptance: { message: 'must be abided' }
end
</pre>
</div>
<p>It can also receive an <code>:accept</code> option, which determines the allowed values
that will be considered as accepted. It defaults to <code>['1', true]</code> and can be
easily changed.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :terms_of_service, acceptance: { accept: 'yes' }
validates :eula, acceptance: { accept: ['TRUE', 'accepted'] }
end
</pre>
</div>
<p>This validation is very specific to web applications and this
'acceptance' does not need to be recorded anywhere in your database. If you
don't have a field for it, the helper will just create a virtual attribute. If
the field does exist in your database, the <code>accept</code> option must be set to
or include <code>true</code> or else the validation will not run.</p><h4 id="validates-associated"><a class="anchorlink" href="#validates-associated">2.2 <code>validates_associated</code></a></h4><p>You should use this helper when your model has associations with other models
and they also need to be validated. When you try to save your object, <code>valid?</code>
will be called upon each one of the associated objects.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Library < ApplicationRecord
has_many :books
validates_associated :books
end
</pre>
</div>
<p>This validation will work with all of the association types.</p><div class="warning"><p>Don't use <code>validates_associated</code> on both ends of your associations.
They would call each other in an infinite loop.</p></div><p>The default error message for <code>validates_associated</code> is <em>"is invalid"</em>. Note
that each associated object will contain its own <code>errors</code> collection; errors do
not bubble up to the calling model.</p><h4 id="confirmation"><a class="anchorlink" href="#confirmation">2.3 <code>confirmation</code></a></h4><p>You should use this helper when you have two text fields that should receive
exactly the same content. For example, you may want to confirm an email address
or a password. This validation creates a virtual attribute whose name is the
name of the field that has to be confirmed with "_confirmation" appended.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :email, confirmation: true
end
</pre>
</div>
<p>In your view template you could use something like</p><div class="code_container">
<pre class="brush: ruby; html-script: true; gutter: false; toolbar: false">
<%= text_field :person, :email %>
<%= text_field :person, :email_confirmation %>
</pre>
</div>
<p>This check is performed only if <code>email_confirmation</code> is not <code>nil</code>. To require
confirmation, make sure to add a presence check for the confirmation attribute
(we'll take a look at <code>presence</code> later on in this guide):</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :email, confirmation: true
validates :email_confirmation, presence: true
end
</pre>
</div>
<p>There is also a <code>:case_sensitive</code> option that you can use to define whether the
confirmation constraint will be case sensitive or not. This option defaults to
true.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :email, confirmation: { case_sensitive: false }
end
</pre>
</div>
<p>The default error message for this helper is <em>"doesn't match confirmation"</em>.</p><h4 id="exclusion"><a class="anchorlink" href="#exclusion">2.4 <code>exclusion</code></a></h4><p>This helper validates that the attributes' values are not included in a given
set. In fact, this set can be any enumerable object.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Account < ApplicationRecord
validates :subdomain, exclusion: { in: %w(www us ca jp),
message: "%{value} is reserved." }
end
</pre>
</div>
<p>The <code>exclusion</code> helper has an option <code>:in</code> that receives the set of values that
will not be accepted for the validated attributes. The <code>:in</code> option has an
alias called <code>:within</code> that you can use for the same purpose, if you'd like to.
This example uses the <code>:message</code> option to show how you can include the
attribute's value. For full options to the message argument please see the
<a href="#message">message documentation</a>.</p><p>The default error message is <em>"is reserved"</em>.</p><h4 id="format"><a class="anchorlink" href="#format">2.5 <code>format</code></a></h4><p>This helper validates the attributes' values by testing whether they match a
given regular expression, which is specified using the <code>:with</code> option.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Product < ApplicationRecord
validates :legacy_code, format: { with: /\A[a-zA-Z]+\z/,
message: "only allows letters" }
end
</pre>
</div>
<p>Alternatively, you can require that the specified attribute does <em>not</em> match the regular expression by using the <code>:without</code> option.</p><p>The default error message is <em>"is invalid"</em>.</p><h4 id="inclusion"><a class="anchorlink" href="#inclusion">2.6 <code>inclusion</code></a></h4><p>This helper validates that the attributes' values are included in a given set.
In fact, this set can be any enumerable object.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Coffee < ApplicationRecord
validates :size, inclusion: { in: %w(small medium large),
message: "%{value} is not a valid size" }
end
</pre>
</div>
<p>The <code>inclusion</code> helper has an option <code>:in</code> that receives the set of values that
will be accepted. The <code>:in</code> option has an alias called <code>:within</code> that you can
use for the same purpose, if you'd like to. The previous example uses the
<code>:message</code> option to show how you can include the attribute's value. For full
options please see the <a href="#message">message documentation</a>.</p><p>The default error message for this helper is <em>"is not included in the list"</em>.</p><h4 id="length"><a class="anchorlink" href="#length">2.7 <code>length</code></a></h4><p>This helper validates the length of the attributes' values. It provides a
variety of options, so you can specify length constraints in different ways:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, length: { minimum: 2 }
validates :bio, length: { maximum: 500 }
validates :password, length: { in: 6..20 }
validates :registration_number, length: { is: 6 }
end
</pre>
</div>
<p>The possible length constraint options are:</p>
<ul>
<li>
<code>:minimum</code> - The attribute cannot have less than the specified length.</li>
<li>
<code>:maximum</code> - The attribute cannot have more than the specified length.</li>
<li>
<code>:in</code> (or <code>:within</code>) - The attribute length must be included in a given
interval. The value for this option must be a range.</li>
<li>
<code>:is</code> - The attribute length must be equal to the given value.</li>
</ul>
<p>The default error messages depend on the type of length validation being
performed. You can personalize these messages using the <code>:wrong_length</code>,
<code>:too_long</code>, and <code>:too_short</code> options and <code>%{count}</code> as a placeholder for the
number corresponding to the length constraint being used. You can still use the
<code>:message</code> option to specify an error message.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :bio, length: { maximum: 1000,
too_long: "%{count} characters is the maximum allowed" }
end
</pre>
</div>
<p>Note that the default error messages are plural (e.g., "is too short (minimum
is %{count} characters)"). For this reason, when <code>:minimum</code> is 1 you should
provide a personalized message or use <code>presence: true</code> instead. When
<code>:in</code> or <code>:within</code> have a lower limit of 1, you should either provide a
personalized message or call <code>presence</code> prior to <code>length</code>.</p><h4 id="numericality"><a class="anchorlink" href="#numericality">2.8 <code>numericality</code></a></h4><p>This helper validates that your attributes have only numeric values. By
default, it will match an optional sign followed by an integral or floating
point number. To specify that only integral numbers are allowed set
<code>:only_integer</code> to true.</p><p>If you set <code>:only_integer</code> to <code>true</code>, then it will use the</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
/\A[+-]?\d+\z/
</pre>
</div>
<p>regular expression to validate the attribute's value. Otherwise, it will try to
convert the value to a number using <code>Float</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Player < ApplicationRecord
validates :points, numericality: true
validates :games_played, numericality: { only_integer: true }
end
</pre>
</div>
<p>Besides <code>:only_integer</code>, this helper also accepts the following options to add
constraints to acceptable values:</p>
<ul>
<li>
<code>:greater_than</code> - Specifies the value must be greater than the supplied
value. The default error message for this option is <em>"must be greater than
%{count}"</em>.</li>
<li>
<code>:greater_than_or_equal_to</code> - Specifies the value must be greater than or
equal to the supplied value. The default error message for this option is
<em>"must be greater than or equal to %{count}"</em>.</li>
<li>
<code>:equal_to</code> - Specifies the value must be equal to the supplied value. The
default error message for this option is <em>"must be equal to %{count}"</em>.</li>
<li>
<code>:less_than</code> - Specifies the value must be less than the supplied value. The
default error message for this option is <em>"must be less than %{count}"</em>.</li>
<li>
<code>:less_than_or_equal_to</code> - Specifies the value must be less than or equal to
the supplied value. The default error message for this option is <em>"must be
less than or equal to %{count}"</em>.</li>
<li>
<code>:other_than</code> - Specifies the value must be other than the supplied value.
The default error message for this option is <em>"must be other than %{count}"</em>.</li>
<li>
<code>:odd</code> - Specifies the value must be an odd number if set to true. The
default error message for this option is <em>"must be odd"</em>.</li>
<li>
<code>:even</code> - Specifies the value must be an even number if set to true. The
default error message for this option is <em>"must be even"</em>.</li>
</ul>
<div class="note"><p>By default, <code>numericality</code> doesn't allow <code>nil</code> values. You can use <code>allow_nil: true</code> option to permit it.</p></div><p>The default error message is <em>"is not a number"</em>.</p><h4 id="presence"><a class="anchorlink" href="#presence">2.9 <code>presence</code></a></h4><p>This helper validates that the specified attributes are not empty. It uses the
<code>blank?</code> method to check if the value is either <code>nil</code> or a blank string, that
is, a string that is either empty or consists of whitespace.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, :login, :email, presence: true
end
</pre>
</div>
<p>If you want to be sure that an association is present, you'll need to test
whether the associated object itself is present, and not the foreign key used
to map the association. This way, it is not only checked that the foreign key
is not empty but also that the referenced object exists.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class LineItem < ApplicationRecord
belongs_to :order
validates :order, presence: true
end
</pre>
</div>
<p>In order to validate associated records whose presence is required, you must
specify the <code>:inverse_of</code> option for the association:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Order < ApplicationRecord
has_many :line_items, inverse_of: :order
end
</pre>
</div>
<p>If you validate the presence of an object associated via a <code>has_one</code> or
<code>has_many</code> relationship, it will check that the object is neither <code>blank?</code> nor
<code>marked_for_destruction?</code>.</p><p>Since <code>false.blank?</code> is true, if you want to validate the presence of a boolean
field you should use one of the following validations:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
validates :boolean_field_name, inclusion: { in: [true, false] }
validates :boolean_field_name, exclusion: { in: [nil] }
</pre>
</div>
<p>By using one of these validations, you will ensure the value will NOT be <code>nil</code>
which would result in a <code>NULL</code> value in most cases.</p><h4 id="absence"><a class="anchorlink" href="#absence">2.10 <code>absence</code></a></h4><p>This helper validates that the specified attributes are absent. It uses the
<code>present?</code> method to check if the value is not either nil or a blank string, that
is, a string that is either empty or consists of whitespace.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, :login, :email, absence: true
end
</pre>
</div>
<p>If you want to be sure that an association is absent, you'll need to test
whether the associated object itself is absent, and not the foreign key used
to map the association.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class LineItem < ApplicationRecord
belongs_to :order
validates :order, absence: true
end
</pre>
</div>
<p>In order to validate associated records whose absence is required, you must
specify the <code>:inverse_of</code> option for the association:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Order < ApplicationRecord
has_many :line_items, inverse_of: :order
end
</pre>
</div>
<p>If you validate the absence of an object associated via a <code>has_one</code> or
<code>has_many</code> relationship, it will check that the object is neither <code>present?</code> nor
<code>marked_for_destruction?</code>.</p><p>Since <code>false.present?</code> is false, if you want to validate the absence of a boolean
field you should use <code>validates :field_name, exclusion: { in: [true, false] }</code>.</p><p>The default error message is <em>"must be blank"</em>.</p><h4 id="uniqueness"><a class="anchorlink" href="#uniqueness">2.11 <code>uniqueness</code></a></h4><p>This helper validates that the attribute's value is unique right before the
object gets saved. It does not create a uniqueness constraint in the database,
so it may happen that two different database connections create two records
with the same value for a column that you intend to be unique. To avoid that,
you must create a unique index on that column in your database.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Account < ApplicationRecord
validates :email, uniqueness: true
end
</pre>
</div>
<p>The validation happens by performing an SQL query into the model's table,
searching for an existing record with the same value in that attribute.</p><p>There is a <code>:scope</code> option that you can use to specify one or more attributes that
are used to limit the uniqueness check:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Holiday < ApplicationRecord
validates :name, uniqueness: { scope: :year,
message: "should happen once per year" }
end
</pre>
</div>
<p>Should you wish to create a database constraint to prevent possible violations of a uniqueness validation using the <code>:scope</code> option, you must create a unique index on both columns in your database. See <a href="http://dev.mysql.com/doc/refman/5.7/en/multiple-column-indexes.html">the MySQL manual</a> for more details about multiple column indexes or <a href="https://www.postgresql.org/docs/current/static/ddl-constraints.html">the PostgreSQL manual</a> for examples of unique constraints that refer to a group of columns.</p><p>There is also a <code>:case_sensitive</code> option that you can use to define whether the
uniqueness constraint will be case sensitive or not. This option defaults to
true.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, uniqueness: { case_sensitive: false }
end
</pre>
</div>
<div class="warning"><p>Note that some databases are configured to perform case-insensitive
searches anyway.</p></div><p>The default error message is <em>"has already been taken"</em>.</p><h4 id="validates-with"><a class="anchorlink" href="#validates-with">2.12 <code>validates_with</code></a></h4><p>This helper passes the record to a separate class for validation.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class GoodnessValidator < ActiveModel::Validator
def validate(record)
if record.first_name == "Evil"
record.errors[:base] << "This person is evil"
end
end
end
class Person < ApplicationRecord
validates_with GoodnessValidator
end
</pre>
</div>
<div class="note"><p>Errors added to <code>record.errors[:base]</code> relate to the state of the record
as a whole, and not to a specific attribute.</p></div><p>The <code>validates_with</code> helper takes a class, or a list of classes to use for
validation. There is no default error message for <code>validates_with</code>. You must
manually add errors to the record's errors collection in the validator class.</p><p>To implement the validate method, you must have a <code>record</code> parameter defined,
which is the record to be validated.</p><p>Like all other validations, <code>validates_with</code> takes the <code>:if</code>, <code>:unless</code> and
<code>:on</code> options. If you pass any other options, it will send those options to the
validator class as <code>options</code>:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class GoodnessValidator < ActiveModel::Validator
def validate(record)
if options[:fields].any?{|field| record.send(field) == "Evil" }
record.errors[:base] << "This person is evil"
end
end
end
class Person < ApplicationRecord
validates_with GoodnessValidator, fields: [:first_name, :last_name]
end
</pre>
</div>
<p>Note that the validator will be initialized <em>only once</em> for the whole application
life cycle, and not on each validation run, so be careful about using instance
variables inside it.</p><p>If your validator is complex enough that you want instance variables, you can
easily use a plain old Ruby object instead:</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validate do |person|
GoodnessValidator.new(person).validate
end
end
class GoodnessValidator
def initialize(person)
@person = person
end
def validate
if some_complex_condition_involving_ivars_and_private_methods?
@person.errors[:base] << "This person is evil"
end
end
# ...
end
</pre>
</div>
<h4 id="validates-each"><a class="anchorlink" href="#validates-each">2.13 <code>validates_each</code></a></h4><p>This helper validates attributes against a block. It doesn't have a predefined
validation function. You should create one using a block, and every attribute
passed to <code>validates_each</code> will be tested against it. In the following example,
we don't want names and surnames to begin with lower case.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates_each :name, :surname do |record, attr, value|
record.errors.add(attr, 'must start with upper case') if value =~ /\A[[:lower:]]/
end
end
</pre>
</div>
<p>The block receives the record, the attribute's name, and the attribute's value.
You can do anything you like to check for valid data within the block. If your
validation fails, you should add an error message to the model, therefore
making it invalid.</p><h3 id="common-validation-options"><a class="anchorlink" href="#common-validation-options">3 Common Validation Options</a></h3><p>These are common validation options:</p><h4 id="allow-nil"><a class="anchorlink" href="#allow-nil">3.1 <code>:allow_nil</code></a></h4><p>The <code>:allow_nil</code> option skips the validation when the value being validated is
<code>nil</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Coffee < ApplicationRecord
validates :size, inclusion: { in: %w(small medium large),
message: "%{value} is not a valid size" }, allow_nil: true
end
</pre>
</div>
<p>For full options to the message argument please see the
<a href="#message">message documentation</a>.</p><h4 id="allow-blank"><a class="anchorlink" href="#allow-blank">3.2 <code>:allow_blank</code></a></h4><p>The <code>:allow_blank</code> option is similar to the <code>:allow_nil</code> option. This option
will let validation pass if the attribute's value is <code>blank?</code>, like <code>nil</code> or an
empty string for example.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Topic < ApplicationRecord
validates :title, length: { is: 5 }, allow_blank: true
end
Topic.create(title: "").valid? # => true
Topic.create(title: nil).valid? # => true
</pre>
</div>
<h4 id="message"><a class="anchorlink" href="#message">3.3 <code>:message</code></a></h4><p>As you've already seen, the <code>:message</code> option lets you specify the message that
will be added to the <code>errors</code> collection when validation fails. When this
option is not used, Active Record will use the respective default error message
for each validation helper. The <code>:message</code> option accepts a <code>String</code> or <code>Proc</code>.</p><p>A <code>String</code> <code>:message</code> value can optionally contain any/all of <code>%{value}</code>,
<code>%{attribute}</code>, and <code>%{model}</code> which will be dynamically replaced when
validation fails. This replacement is done using the I18n gem, and the
placeholders must match exactly, no spaces are allowed.</p><p>A <code>Proc</code> <code>:message</code> value is given two arguments: the object being validated, and
a hash with <code>:model</code>, <code>:attribute</code>, and <code>:value</code> key-value pairs.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
# Hard-coded message
validates :name, presence: { message: "must be given please" }
# Message with dynamic attribute value. %{value} will be replaced with
# the actual value of the attribute. %{attribute} and %{model} also
# available.
validates :age, numericality: { message: "%{value} seems wrong" }
# Proc
validates :username,
uniqueness: {
# object = person object being validated
# data = { model: "Person", attribute: "Username", value: <username> }
message: ->(object, data) do
"Hey #{object.name}!, #{data[:value]} is taken already! Try again #{Time.zone.tomorrow}"
end
}
end
</pre>
</div>
<h4 id="on"><a class="anchorlink" href="#on">3.4 <code>:on</code></a></h4><p>The <code>:on</code> option lets you specify when the validation should happen. The
default behavior for all the built-in validation helpers is to be run on save
(both when you're creating a new record and when you're updating it). If you
want to change it, you can use <code>on: :create</code> to run the validation only when a
new record is created or <code>on: :update</code> to run the validation only when a record
is updated.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
# it will be possible to update email with a duplicated value
validates :email, uniqueness: true, on: :create
# it will be possible to create the record with a non-numerical age
validates :age, numericality: true, on: :update
# the default (validates on both create and update)
validates :name, presence: true
end
</pre>
</div>
<p>You can also use <code>on:</code> to define custom contexts. Custom contexts need to be
triggered explicitly by passing the name of the context to <code>valid?</code>,
<code>invalid?</code>, or <code>save</code>.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :email, uniqueness: true, on: :account_setup
validates :age, numericality: true, on: :account_setup
end
person = Person.new(age: 'thirty-three')
person.valid? # => true
person.valid?(:account_setup) # => false
person.errors.messages
# => {:email=>["has already been taken"], :age=>["is not a number"]}
</pre>
</div>
<p><code>person.valid?(:account_setup)</code> executes both the validations without saving
the model. <code>person.save(context: :account_setup)</code> validates <code>person</code> in the
<code>account_setup</code> context before saving.</p><p>When triggered by an explicit context, validations are run for that context,
as well as any validations <em>without</em> a context.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :email, uniqueness: true, on: :account_setup
validates :age, numericality: true, on: :account_setup
validates :name, presence: true
end
person = Person.new
person.valid?(:account_setup) # => false
person.errors.messages
# => {:email=>["has already been taken"], :age=>["is not a number"], :name=>["can't be blank"]}
</pre>
</div>
<h3 id="strict-validations"><a class="anchorlink" href="#strict-validations">4 Strict Validations</a></h3><p>You can also specify validations to be strict and raise
<code>ActiveModel::StrictValidationFailed</code> when the object is invalid.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :name, presence: { strict: true }
end
Person.new.valid? # => ActiveModel::StrictValidationFailed: Name can't be blank
</pre>
</div>
<p>There is also the ability to pass a custom exception to the <code>:strict</code> option.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">
class Person < ApplicationRecord
validates :token, presence: true, uniqueness: true, strict: TokenGenerationException
end
Person.new.valid? # => TokenGenerationException: Token can't be blank
</pre>
</div>
<h3 id="conditional-validation"><a class="anchorlink" href="#conditional-validation">5 Conditional Validation</a></h3><p>Sometimes it will make sense to validate an object only when a given predicate
is satisfied. You can do that by using the <code>:if</code> and <code>:unless</code> options, which
can take a symbol, a <code>Proc</code> or an <code>Array</code>. You may use the <code>:if</code>
option when you want to specify when the validation <strong>should</strong> happen. If you
want to specify when the validation <strong>should not</strong> happen, then you may use the
<code>:unless</code> option.</p><h4 id="using-a-symbol-with-if-and-unless"><a class="anchorlink" href="#using-a-symbol-with-if-and-unless">5.1 Using a Symbol with <code>:if</code> and <code>:unless</code></a></h4><p>You can associate the <code>:if</code> and <code>:unless</code> options with a symbol corresponding
to the name of a method that will get called right before validation happens.
This is the most commonly used option.</p><div class="code_container">
<pre class="brush: ruby; gutter: false; toolbar: false">