Mongo Update Embedded Plugin for Grails 3.3.x

+Mongo Update Embedded Plugin >= 2.0.0 supports Grails 3.3.x +Mongo Update Embedded Plugin <= 1.0.0 supports Grails 3.2.x (Tested upto 3.2.5)

Latest Version (2.0.1)

Installation

Add this to the dependencies block of your build.gradle file.

#!groovy

dependencies {
    compile "com.causecode.plugins:mongo-update-embedded:$VERSION"
}

Usage

The MongoDB database does not support the concept of joins, hence as an alternative, we use the concept of embedded documents. Refer to the Grails docs for embedded.

Embedding entire domain objects within another domain object would make the data redundant. If you just use the reference of the object and does not embed it (using the static embedded field), then you will have to do multiple queries to fetch the object that is referenced.

To avoid redundant data in the database as well as multiple queries, we can create simple Groovy classes under src/main/groovy with the most relevant fields of the domain class and then embed them as an embedded object of the parent domain class.

In such case, whenever any domain object is updated, it's embedded object in some other domain remains unchanged. This plugin solves this problem by updating those embedded instances.

Implementing in your Grails App

You will have to create a class that will represent embedded objects of the parent domain class.

This class needs to implement the trait EmbeddableDomain which contains some necessary methods to treat a class as an embeddable class.

** Override the UpdateEmbeddedInstancesJob schedule ** By default it is set to update at every 2 minutes but if you want to override the schedule, Add the following block in the application.groovy of installing app.

// Override startDelay and repeatInterval of UpdateEmbeddedInstancesJob
jobs {
    mongo.update.embedded.startDelay = 120000 // 120 Seconds
    mongo.update.embedded.repeatInterval = 30000 // 30 seconds
}

Example: For a domain class User you can create an embedded class called EmUser under src/main/groovy.

#!groovy

class EmUser implements EmbeddableDomain {

    ObjectId instanceId
    String email
    String username

    EmUser(ObjectId instanceId, String username, String email) {
        this.instanceId = instanceId
        this.username = username
        this.email = email
    }
}

Important: The field name representing the id of the domain class within the embedded class needs to be instanceId, else it will not work.

Note: The default implementation assumes the name format to be Em prefixed to the domain class name. But you can create your own naming convention by overriding the resolveParentDomainClass method which returns the domain name of the actual parent domain.

Your domain class should have a method named getEmbeddedInstance which returns an object of the embeddable class for a domain instance.

#!groovy

class User {

    ObjectId id
    String email
    String username

    // Other fields here...

    EmUser getEmbeddedInstance() {
        return new EmUser(this.id, this.username, this.email)
    }
}

Finally, you can embed this class's object using the static embedded fields in any other domain class.

Example: For a domain class UserProfile, you can create a field EmUser user and then mark the field as embedded as static embedded = ['user'].

Note: If you change the field name mapping using static mapping block, the plugin will not update the embedded instance.