Delete associated model with ember-data

Question

I have two models:

App.User = DS.Model.create({
  comments: DS.hasMany('App.Comment')
});

App.Comment = DS.Model.create({
  user: DS.belongsTo('App.User')
});

When a user is deleted, it also will delete all its comments on the backend, so I should delete them from the client-side identity map.

I'm listing all the comments on the system from another place, so after deleting a user it would just crash.

Is there any way to specify this kind of dependency on the association? Thanks!

Answer 1

I use a mixin when I want to implement this behaviour. My models are defined as follows:

App.Post = DS.Model.extend(App.DeletesDependentRelationships, {
    dependentRelationships: ['comments'],

    comments: DS.hasMany('App.Comment'),
    author: DS.belongsTo('App.User')
});

App.User = DS.Model.extend();

App.Comment = DS.Model.extend({
    post: DS.belongsTo('App.Post')
});

The mixin itself:

App.DeletesDependentRelationships = Ember.Mixin.create({

    // an array of relationship names to delete
    dependentRelationships: null,

    // set to 'delete' or 'unload' depending on whether or not you want
    // to actually send the deletions to the server
    deleteMethod: 'unload', 

    deleteRecord: function() {
        var transaction = this.get('store').transaction();
        transaction.add(this);
        this.deleteDependentRelationships(transaction);
        this._super();
    },

    deleteDependentRelationships: function(transaction) {
        var self = this;
        var klass = Ember.get(this.constructor.toString());
        var fields = Ember.get(klass, 'fields');

        this.get('dependentRelationships').forEach(function(name) {
            var relationshipType = fields.get(name);
            switch(relationshipType) {
                case 'belongsTo': return self.deleteBelongsToRelationship(name, transaction);
                case 'hasMany': return self.deleteHasManyRelationship(name, transaction);
            }
        });
    },

    deleteBelongsToRelationship: function(name, transaction) {
        var record = this.get(name);
        if (record) this.deleteOrUnloadRecord(record, transaction);
    },

    deleteHasManyRelationship: function(key, transaction) {
        var self = this;

        // deleting from a RecordArray doesn't play well with forEach, 
        // so convert to a normal array first
        this.get(key).toArray().forEach(function(record) {
            self.deleteOrUnloadRecord(record, transaction);
        });
    },

    deleteOrUnloadRecord: function(record, transaction) {
        var deleteMethod = this.get('deleteMethod');
        if (deleteMethod === 'delete') {
            transaction.add(record);
            record.deleteRecord();
        }
        else if (deleteMethod === 'unload') {
            var store = this.get('store');
            store.unloadRecord(record);
        }
    }
});

Note that you can specify via deleteMethod whether or not you want to send the DELETE requests to your API. If your back-end is configured to delete dependent records automatically, then you will want to use the default.

Here's a jsfiddle that shows it in action.