Observable-based queries re-emit lists matching previous queries

[cartant]

Version info

Angular: 2.4.7

Firebase: 3.6.9

AngularFire: 2.0.0-beta.8

Other (e.g. Ionic/Cordova, Node, browser, operating system): N/A

How to reproduce these conditions

There is a plunk here that demonstrates the bug.

Steps to set up and reproduce

Run the above plunk which:

• sets up some initial content
• runs an observable-based query to select odd numbers
• re-runs the query to select even numbers
• writes more data - including both an even and an odd number - to the database

Note that after more data is written, the list observable emits a list that matches the first (odd) query and then the second (even) query.

The bug is due to mergeMap - which is used here - the behaviour of which is to allow merged observables to continue to emit. switchMap should be used instead.

Expected behavior

When an observable query changes, the list observable should emit only lists that relate to the changed query.

Actual behavior

When an observable query changes, the list observable emits lists that relate to the changed query and any previous queries.