How can I filter a hasMany relationship?

Question

I have a user object that is loaded into the session at session.user. The user can be assigned many roles. Here's what that looks like on the model:

App.User = DS.Model.extend({
    roles       : DS.hasMany('role'),
    ...
}

The roles are loaded with the user as embedded records. I can verify they are being successfully loaded into the ember-data store and the relationship between the user and the role is all good.

What I'd like to be able to do, is get one of the user's role based upon a role property. I've tried

this.get('session.user.roles').then(function (roles) {
    return roles.filterBy('propertyName', 'propertyValue');
});

but I don't believe the get method returns a promise like the store.find() method does. What methods are provided to me to filter the roles?

score 3 · Accepted Answer · answered Sep 10 '14 at 23:58

3

The way you are doing it would be available as a result of a tacked on promise. Let me see if I can break it down.

Here's the long way of showing where filtered roles will be available:

var rolesPromise = this.get('session.user.roles');

var filteredRolesPromise = rolesPromise.then(function (roles) {
    return roles.filterBy('propertyName', 'propertyValue');
});

filteredRolesPromise.then(function(filteredRoles){
    // available here
    console.log(filteredRoles.get('length'));
});

Here's the short way of showing where filtered roles will be available:

this.get('session.user.roles').then(function (roles) {
   var filteredRoles = roles.filterBy('propertyName', 'propertyValue');
   // available here
   console.log(filteredRoles.get('length'));
});

or

var foo = this.get('session.user.roles').then(function (roles) {
   return roles.filterBy('propertyName', 'propertyValue');
}).then(function(filteredRoles){
   // available here
   console.log(filteredRoles.get('length'));
});

returning the property to the promise just makes it available to the next tacked on promise, it doesn't assign it to the variable (foo in the case right here).

This here helps with promises: https://www.youtube.com/watch?v=8WXgm4_V85E

Essentially I'm saying since roles is an async property you'll never be able to safely use it in a synchronous fashion.

answered Sep 10 '14 at 23:58

Kingpin2k

47,277
10
78
96

Oh! This is your presentation. Radical. Good to put a face to your username. I'll definitely watch this. The thing is, roles is not an async relationship. They're defined as `DS.hasMany('role')` and I'm using the `DS.EmbeddedRecordsMixin` to serialize the embeds, which is working great. When I `this.get('session.user.roles')`, I don't get back a promise, but a roles array object, I think. – ToddSmithSalter Sep 11 '14 at 02:23
I can confirm that when I do `this.get('session.user.roles')` I get a DS.ManyArray object in return. I understand that DS.ManyArray extends DS.RecordsArray, which extends Ember.ArrayProxy. Shouldn't I have access to the filter method then? Instead, I always get error `Uncaught TypeError: Cannot read property 'filter' of undefined`. – ToddSmithSalter Sep 11 '14 at 05:06
Thanks for that link. I did manage to get and filter the roles with a 4 layer-cake of promises. The issue I'm having now is returning the boolean value of the promise from the method. I've tried setting it on a scoped variable, but that doesn't seem to stick. – ToddSmithSalter Sep 11 '14 at 18:10
Would you mind tossing up a new question showing the cake of promises and what scope you're referring to? – Kingpin2k Sep 11 '14 at 18:56
Sure thing. Here's the followup http://stackoverflow.com/questions/25795629/how-do-i-return-the-boolean-value-from-this-layer-cake-of-promises – ToddSmithSalter Sep 11 '14 at 19:32

How can I filter a hasMany relationship?

1 Answers1