EmberData: Two models related with hasMany relationships

Question

I have an application logic that requires two models to have reciprocal hasMany relationships. As an example, imagine a set of GitHub issues that can be tagged with several labe

Answer 1

Many to Many relationships are not yet supported in ember-data. For the moment, one possible workaround is to manually manage the join table.

A = DS.Model.extend({
  abs: DS.hasMany('Ab'),

  bs: function () {
    return this.get('abs').getEach('b'); 
  }
});

Ab = DS.Model.extend({
  a: DS.belongsTo('A'),
  b: DS.belongsTo('b')
});

B = DS.Model.extend({
  abs: DS.hasMany('Ab'),

  bs: function () {
    return this.get('abs').getEach('a'); 
  }
});

This is just the starting point. You need then to customize your models and adapter in order to send/receive/persist records in a working manner

For example, in our app, we introduce an { includedJoin: true } option inside the hasMany relations, and declare the join table as a JoinModel

A = DS.Model.extend({
  abs: DS.hasMany('Ab', {includeJoin: true}),
  ...
});

DS.JoinModel = DS.Model.extend();

Ab = DS.JoinModel.extend({
  ... belongsTo relationships ...
});

Then in the Adapter, we override the create/update/delete methods in order to ignore the joins table lifecycle in the store

createRecords: function (store, type, records) {
  if (!DS.JoinModel.detect(type)) {
    this._super(store, type, records);
  }
}

Finally, in the serializer, we override the addHasMany function in order to send the join data to the server as embedded ids in the parent models.

addHasMany: function (hash, record, key, relationship) {
  var 
    options = relationship.options,
    children = [];

  //we only add join models, use of `includeJoin`
  if (options.includedJoin) {
    record.get(relationship.key).forEach(function (child) {
      children.pushObject(child.toJSON({
        includeId: true
      }));
    });
    hash[key] = children;
  }
}

Server-side we are using Rails with ActiveModelSerializer, so the only little-tricky-customization is when when we update the parent models, we manually manage the joins relation, and create/delete entries in the join table.