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thebarty:denormalized-views
A toolkit that helps you to create "read-only" denormalized mongo-"views" (collections), which are especially useful for search-able tables, reporting databases or other read-heavy scenarios (see "Example Use-Case" for a quick overview). It's concept also matches with CQRS's "materialized views" concept.
The resulting "view"-collection can then be used with tools like aldeed:tabular, or easy:search to display and search related data.
Simply define how the data shall be collected based on a "source"-collection. Whenever a change happens in "source"-collection (insert | update | remove), the "view"-collection will automatically be refreshed.
Additionally you can hookup "related"-collections to automatically refresh the "source"-collection or trigger manual refreshes (if necessary at all).
Table of Contents generated with DocToc
- Installation
- Example Use-Case
- Setup by
addView() - Staying in sync
- Debug mode
DenormalizedViews.Debug = true - Defer syncing via
DenormalizedViews.DeferWriteAccess - A full example containing all options
- Latency compensation?
- Open Todos
- How to contribute to this package
- Research Resources
In your Meteor app directory, enter:
$ meteor add thebarty:denormalized-views
Let's say you have 3 collections:
- Posts (relate to 1 author & multiple comments)
- Comments (relate to 1 post)
- Authors (relate to multiple posts)
In your app you want to show a list of posts with infos about their related authors and comments. Additionally you want to give the user the option to search by the following:
- search the post-text (field "text" in collection "Posts")
- search the comment-text (field "text" in collection "Comments")
- search the author-name (field "name" in collection "Author")
You know that aldeed:tabular is a great package to list a collection in the frontend. Although it can easily show joined collection thru a package like reywood:publish-composite, it does NOT support search over joined collections. Here is where denormalized-views comes into play: simply create a denormalized "view"-collection and use it to display and search data thru tabular.
Use addView() to define how your "view"-collection collects its data. It all starts at the "source"-collection (p.e. Posts): data of the "source"-collection will automatically be copied 1-to-1 to the "view"-collection (= the "view"-collection). Scroll down to see the first code.
The concept is that your "source"-collection is writable, while your "view"-collection is read-only. DO NOT write to your "view"-collection - otherwise data will get out of sync!
The synchronization is "one way" and will run anytime the "source"-collection receives an Mongo- insert, update or remove-command. The effected docs will then process via your sync:- && postSync-definitions and stored to the "view"-collection.
Of course the _id will be the same in both collections. A remove on the "source"-collection will remove the doc from "view"-collection.
Within the sync-property you extend the target document and hand each new property a function to collect the denormalized data and return it.
Start by defining your synchronization:
import { DenormalizedViews } from 'meteor/thebarty:denormalized-views'
const IDENTIFIER = 'identifier' // unique id
const PostsView = new Mongo.Collection('postsview') // create "view"-collection
DenormalizedViews.addView({
identifier: IDENTIFIER,
sourceCollection: Posts,
viewCollection: PostsView,
sync: {
// In here you extend the doc of the "source"-collection
// in order to be put into the "view"-collection.
//
// Simply define a property and assign it a function.
// Within the function: Collect the data you need
// and return it. If you return "undefined",
// the property will removed from the doc.
//
// The function will be passed 2 parameters:
// 1) the current doc of the "source"-Collection
// 2) the current userId (when available)
//
// Some examples:
authorCache: (post, userId) => {
return Authors.findOne(post.authorId)
},
categoryCache: (post, userId) => {
return Categories.findOne(post.categoryId)
},
commentsCache: (post, userId) => {
const comments = []
for (const commentId of post.commentIds) {
const comment = Comments.findOne(commentId)
comments.push(comment)
}
return comments
},
},
})There is also a postSync: property, which acts the same as sync:, but it runs after sync: has collected data, meaning that the passed doc will already contain the new properties from sync:. You can use postSync: to create joined search fields or get creative.
// ... continuing the example from above
postSync: {
// This will be called AFTER ``sync:`` has attached
// new data to the doc, so you can use this to create
// joined search fields, or get creative.
wholeText: (post, userId) => {
let authorText = ''
if (post.authorCache) {
authorText = post.authorCache.name
}
return `${post.text}, ${_.pluck(post.commentsCache, 'text').join(', ')}, ${authorText}`
},
numberOfComments: (post, userId) => {
return post.commentsCache.length
},
},By default the whole doc from your "source"-collection will be copied to "view"-collection. If you want to restrict the fields being copied you can use the pick-option:
DenormalizedViews.addView({
identifier: IDENTIFIER,
sourceCollection: Posts,
viewCollection: PostsView,
pick: ['text'], // (optional) set to pick specific fields
// from sourceCollection
// continue with
// ... sync:
// ... postSync:
})In some useCases you ONLY want to create a doc in the "view"-collection, if it passes a FILTER. Use the filter()-option to specify this condition and have it return true, if you want the doc to be created. If the function returns anything else than true, there will be no further processing and an existing doc (with the same _id� will be removed).
Example:
DenormalizedViews.addView({
identifier: IDENTIFIER,
sourceCollection: Posts,
viewCollection: PostsView,
filter(doc) {
if (doc.author==='Donald') {
return true // process ONLY posts that where created by "Donald"
}
return false
},
// continue with
// ... sync:
// ... postSync:
})If you need to do some processing related to the creation of a "view"-doc, you can use the postHook-option. It will be called after a successful insert-/update-/remove- of the "view"-collection has happened and contains the resulting "view"-doc as the first- and (if exists) the userId as the second-parameter.
Example:
DenormalizedViews.addView({
identifier: IDENTIFIER,
sourceCollection: Posts,
viewCollection: PostsView,
// ... sync:
// ... postSync:
postHook(doc, userId) {
// do something afterwards
},
})If within your app you only write to "source"-collection, that is all you have to do, because by setting up addView you enabled the automatic synchronization between "source"-Collection and "view"-collection.
BUT changes made to other "related"-collections will potentially invalidate data within your "view"-collection. In our example this would happen when you update Authors.name. (p.e. PostsView.authorsCache.name will then contain the wrong old name)
There are 2 options to keep the "view"-collection in sync with "related"-collection:
- hook up the "related"-collection via
refreshByCollection()and let this package do the rest - do it manually via
refreshManually(identifier)
Recommendation: Start with option 1) and use option 2) if needed at all.
Setup a refreshByCollection() to automatically synchronize changes made to a "related"-collection. Your task in here is to tell the "view"-collection which _ids shall be refreshed:
Within the refreshIds-parameter's function return an array of _ids. Those _ids will then be refreshed within "view"-collection. The first parameter in this function gives you the current doc change in the "related"-collection.
Within the relatedCollection parameter you define a function that returns the instance of the "related"-collection. By doing so we support circular-imports, p.e. where a "Product"-collection refreshes the "Category"-view and a "Category"-collection refreshes the "Product"-view. Read [4] for more infos.
If you return false, undefined or null a refresh will NOT be triggered.
DenormalizedViews.refreshByCollection({
identifier: IDENTIFIER,
relatedCollection: Authors,
refreshIds: (author, authorPrevious, userId) => {
// The function is passed 3 parameters
// 1) The current doc changed within the "related"-collection
// 2) The previous doc changed within the "related"-collection
// (this is available on Mongo-"update"-modifiers)
// 3) The current userId (if available)
// Return an array of _ids that should be updated in "view"-collection.
// Returning false, an empty array or undefined, will simply
// not refresh anything.
const posts = Posts.find({ authorId: author._id }).fetch()
return _.pluck(posts, '_id')
},
})
// Example2:
// if you store references within the related collection,
// be sure to union all affected _ids in doc & docPrevious
DenormalizedViews.refreshByCollection({
identifier: DENORMALIZED_POST_COLLECTION,
relatedCollection: Categories,
refreshIds: (doc, docPrevious, userId) => {
if (docPrevious) {
// update
return _.union(doc.postIds, docPrevious.postIds)
} else {
// insert | remove
return doc.postIds
}
},
})There might be places where you want to manually refresh the "view"-collection, p.e. in a Meteor.method. You can use refreshManually() to do so:
// this is the manual way of doing it,
// p.e. from a ``Meteor.method``
DenormalizedViews.refreshManually({
identifier: IDENTIFIER,
refreshIds: [Mongo._id], // _id-array of posts that should be updated
})If you ever want to manually refresh the whole "view"-collection", you can use refreshAll(). Filter will be applied, if defined via filter().
Note that this is the slowest option, because the whole table will be refreshed.
// simply pass the identifier
DenormalizedViews.refreshAll(IDENTIFIER)import { DenormalizedViews } from 'thebarty:denormalized-views'
// enable logs
DenormalizedViews.Debug = trueIf you don't care about data being sync 100% real-time and want to relax the server, you can switch on DenormalizedViews.DeferWriteAccess = true. This will wrap all insert- | updates– | removes-commands into a Meteor.defer() an make those writes run asynchronously in the background. Data will take a bit longer to be synced to the "view"-collections. By default this setting is switched off.
import { DenormalizedViews } from 'thebarty:denormalized-views'
// enable Meteor.defer() for writes
DenormalizedViews.DeferWriteAccess = truePlease have a look at the tests in "denormalized-views.tests.js" for more details.
import { DenormalizedViews } from 'meteor/thebarty:denormalized-views'
const IDENTIFIER = 'identifier' // unique id
const PostsView = new Mongo.Collection('PostsView')
DenormalizedViews.addView({
identifier: IDENTIFIER, // unique id for synchronization
sourceCollection: Posts,
viewCollection: PostsView,
pick: ['text'], // (optional)
filter(post) {
if (post.author==='Donald') {
return true // process ONLY posts that where created by "Donald"
}
return false
},
sync: {
authorCache: (post, userId) => {
return Authors.findOne(post.authorId)
},
categoryCache: (post, userId) => {
return Categories.findOne(post.categoryId)
},
commentsCache: (post, userId) => {
const comments = []
for (const commentId of post.commentIds) {
const comment = Comments.findOne(commentId)
comments.push(comment)
}
return comments
},
},
postSync: {
wholeText: (post, userId) => {
let authorText = ''
if (post.authorCache) {
authorText = post.authorCache.name
}
return `${post.text}, ${_.pluck(post.commentsCache, 'text').join(', ')}, ${authorText}`
},
numberOfComments: (post, userId) => {
return post.commentsCache.length
},
},
postHook(post, userId) {
// do something afterwards
},
})Note that we run database-queries ONLY on the server, meaning that the client will receive new data via pub/sub on the "view"-collection. Tools like "aldeed:tabular" have build-in mechanisms to relax the client and only publish the docs currently needed.
- Receive feedback from the community
Lets make this perfect and collaborate. This is how to set up your local testing environment:
- run "meteor create whatever; cd whatever; mkdir packages;"
- clone this package into the packages dir, p.e. "cd packages; git clone https://github.com/thebarty/meteor-denormalized-views.git denormalized-views"
- run tests from the root (/whatever/.) of your project like
meteor test-packages ./packages/meteor-denormalized-views/ --driver-package=cultofcoders:mocha - develop, write tests, and submit a pull request
- [1] https://themeteorchef.com/snippets/using-unblock-and-defer-in-methods/#tmc-when-to-use-unblock-vs-defer When to use Meteor.defer(). Inspiration our
DenormalizedViews.DeferWriteAccess-setting. - [2] http://martinfowler.com/bliki/CQRS.html
- [3] http://martinfowler.com/bliki/ReportingDatabase.html
- [4] https://msdn.microsoft.com/en-us/library/dn589782.aspx Materialized-Views concept