Room - LiveData observer does not trigger when database is updated

Question

I am trying to find out in the code below, why is it that Room\'s LiveData observable does not give me new shifts once I populate the database with new data.

This is

Answer 1

In my case, it was because I was using a MediatorLiveData to convert the entities returned from the database and forgot to call setValue() with the converted result, so the mediator was only relying requests to the database but never notifying results.

override fun getItems() = MediatorLiveData<List<Item>>().apply {
    addSource(itemDao().getItems()) {
        // I was previously only converting the items, without calling 'value ='
        value = it.map(ItemWithTags::toDto)
    }
}

Answer 2

I had a similar problem using Dagger 2 that was caused by having different instances of the Dao, one for updating/inserting data, and a different instance providing the LiveData for observing. Once I configured Dagger to manage a singleton instance of the Dao, then I could insert data in the background (in my case in a Service) while observing LiveData in my Activity - and the onChange() callback would be called.

It comes down to the instance of the Dao must be the same instance that is inserting/updating data and providing LiveData for observation.