AngularFire Database Query

[Richard Marais]

I am using Ionic 2 and Firebase to build a chat app.

I have the following code, that creates an entry:

    import {

      FirebaseAuth,

      AngularFire,

      FirebaseListObservable

    } from 'angularfire2';

    

        public af: AngularFire

                ...

            let memberIds: string[] = [senderId, receiverId];

                ...

            this.af.database.list('/chat/').push({

              memberIds: memberIds,

              negativtimestamp: -Date.now()

            })

As you can see, it adds a `chat` for the specified `memberIds` made up of a `senderId` and a `receiverId`.

The following code, returns a list of all the `chats`.

    this.firelist = this.af.database.list('/chat/', {

      query: {

        orderByChild: 'negativtimestamp',

      }

    });

Now, I want to only be able to retrieve the `chats` for specified `memberIds`.

**Question**

How do I retrieve a list of `chats` for only a specified `senderId` or `receiverId`? i.e. The `chats` that contain either a matching `senderId` or `receiverId` in the `memberIds`.

Any help appreciated.

Note:

I think I am supposed to use equalTo in the query. But not sure how to yet.

[Kato Richardson]

Hi Richard,

Starting context:

• Security rules are not filters
  
• You can’t query on multiple fields. You have to either aggregate the fields or join the data client-side. More reading here and here.
  
• NoSQL data modeling techniques
• Array-like behaviors in Firebase

So first off, don't use arrays. Start with something like the following:

/rooms/$chatid/members/aarav => true

/rooms/$chatid/members/mary => true

/messages/$chatid/$messageid => { ..., timestamp }

Now you can query with something like the following:

var authUid = 'aarav';
var chatId = 'room 1';
var ref = firebase.database().ref();

// query to fetch all rooms that Mary is a member of
var roomQuery = ref.child('rooms').orderByChild('members/' + authUid).equalTo(true);

// query to fetch messages for a single room
var messageQuery = ref.child('messages').child( chatId ).orderByChild('timestamp').limitToLast( 50 );

If you're looking to aggregate all messages from any chat that aarav can access, then you want to create a per-user feed and write the messages into each user's feed as they are created, similar to how Facebook and Twitter manage these.

☼, Kato

​

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Kato Richardson |

Developer Programs Eng |

kato...@google.com |

775-235-8398

[Kato Richardson]

Also see our sample apps.