#130 - Add #to_sql query set method

docs/docs/models-and-databases/reference/query-set.md

@@ -687,6 +687,25 @@ Order.all.sum(:amount)  # Calculates the total amount across all orders
 # => 7
 ```
 
+### `to_s`
+
+Returns a string representation of the considered query set.
+
+### `to_sql`
+
+Returns the SQL representation of the considered query set.
+
+For example:
+
+```crystal
+Tag.filter(name__startswith: "r").to_sql
+# => "SELECT app_tag.id, app_tag.name, app_tag.is_active FROM \"app_tag\" WHERE app_tag.name LIKE $1"
+```
+
+:::note
+The outputted SQL will vary depending on the database backend in use.
+:::
+
 ### `update`
 
 Updates all the records matched by the current query set with the passed values.

spec/marten/db/connection/base_spec.cr

@@ -33,6 +33,20 @@ describe Marten::DB::Connection::Base do
 
       sql.should eq "SELECT * FROM my_table WHERE id = 1"
     end
+
+    it "rejects empty strings" do
+      conn = Marten::DB::Connection::SQLite.new(Marten::Conf::GlobalSettings::Database.new("default"))
+
+      sql = conn.build_sql do |s|
+        s << "SELECT *"
+        s << ""
+        s << "FROM my_table"
+        s << ""
+        s << "WHERE id = 1"
+      end
+
+      sql.should eq "SELECT * FROM my_table WHERE id = 1"
+    end
   end
 
   describe "#id" do

spec/marten/db/query/set_spec.cr

@@ -2709,6 +2709,14 @@ describe Marten::DB::Query::Set do
     end
   end
 
+  describe "#to_sql" do
+    it "produces the output of the query SQL representation" do
+      qs = Marten::DB::Query::Set(Tag).new.filter(name: "ruby")
+
+      qs.to_sql.should eq qs.query.to_sql
+    end
+  end
+
   describe "#update" do
     it "allows to update the records matching a given queryset with values specified as keyword arguments" do
       user_1 = TestUser.create!(username: "abc", email: "abc@example.com", first_name: "John", last_name: "Doe")

spec/marten/db/query/sql/query_spec.cr

@@ -2198,6 +2198,33 @@ describe Marten::DB::Query::SQL::Query do
     end
   end
 
+  describe "#to_sql" do
+    it "produces the expected output" do
+      query = Marten::DB::Query::SQL::Query(Tag).new
+      query.add_query_node(Marten::DB::Query::Node.new(name__startswith: "r"))
+
+      for_mysql do
+        query.to_sql.should eq(
+          "SELECT app_tag.id, app_tag.name, app_tag.is_active " \
+          "FROM `app_tag` WHERE app_tag.name LIKE BINARY ? LIMIT 18446744073709551615"
+        )
+      end
+
+      for_postgresql do
+        query.to_sql.should eq(
+          "SELECT app_tag.id, app_tag.name, app_tag.is_active FROM \"app_tag\" WHERE app_tag.name LIKE $1"
+        )
+      end
+
+      for_sqlite do
+        query.to_sql.should eq(
+          "SELECT app_tag.id, app_tag.name, app_tag.is_active " \
+          "FROM \"app_tag\" WHERE app_tag.name LIKE ? ESCAPE '\\' LIMIT -1"
+        )
+      end
+    end
+  end
+
   describe "#update_with" do
     it "allows to update the records matching a given query and returns the number of affected rows" do
       user_1 = TestUser.create!(username: "abc", email: "abc@example.com", first_name: "John", last_name: "Doe")

src/marten/db/connection/base.cr

@@ -83,7 +83,7 @@ module Marten
         # Allows to conveniently build a SQL statement by yielding an array of nillable strings.
         def build_sql(&)
           yield (clauses = [] of String?)
-          clauses.compact!.join " "
+          clauses.compact!.reject(&.try(&.empty?)).join " "
         end
 
         # Returns the identifier of the connection.

src/marten/db/query/set.cr

@@ -1074,6 +1074,11 @@ module Marten
           inspect(io)
         end
 
+        # Returns the SQL representation of the current query set.
+        def to_sql : String
+          @query.to_sql
+        end
+
         # Updates all the records matched by the current query set with the passed values.
         #
         # This method allows to update all the records that are matched by the current query set with a hash or a named

src/marten/db/query/sql/query.cr

@@ -283,6 +283,10 @@ module Marten
             )
           end
 
+          def to_sql : String
+            build_query.first
+          end
+
           def update_with(values : Hash(String | Symbol, Field::Any | DB::Model))
             values_to_update = Hash(String, ::DB::Any).new
             related_values_to_update = Hash(DB::Model.class, Hash(String | Symbol, Field::Any | DB::Model)).new