Firebase: Multi Location Update using Firebase Object Observable - arrays

Question

I'm trying to work out how to do a multi-location update using the FirebaseObjectObservable.
This is what my data looks like.
recipes: {
-R1: {
name: 'Omelette',
ingredients: ['-I1']
}
}
ingredients: {
-I1: {
name: 'Eggs',
recipes: ['-R1']
},
-I2: {
name: 'Cheese',
recipes: []
}
}
I want to then update that recipe and add an extra ingredient.
const recipe = this.af.database.object(`${this.path}/${key}`);
recipe.update({
name: 'Cheesy Omelette',
ingredients: ['-I1', '-I2']
});
And to do multi-location updates accordingly:
recipes: {
-R1: {
name: 'Cheesy Omelette',
ingredients: ['-I1', '-I2'] // UPDATED
}
}
ingredients: {
-I1: {
name: 'Eggs',
recipes: ['-R1']
},
-I2: {
name: 'Cheese',
recipes: ['-R1'] // UPDATED
}
}
Is this possible in Firebase? And what about the scenario where an update causes 1000 writes.

Answer 1

Storing your ingredients in an array makes it pretty hard to add an ingredient. This is because arrays are index-based: in order to add an item to an array, you must know how many items are already in that array.
Since that number requires a read from the database, the code becomes pretty tricky. The most optimal code I can think of is:
recipe.child("ingredients").orderByKey().limitToLast(1).once("child_added", function(snapshot) {
var updates = {};
updates[parseNum(snapshot.key)+1] = "-I2";
recipe.child("ingredients").update(updates);
});
And while this is plenty tricky to read, it's still not very good. If multiple users are trying to change the ingredients of a recipe at almost the same time, this code will fail. So you really should be using a transaction, which reads more data and hurts scalability of your app.
This is one of the reasons why Firebase has always recommended against using arrays.
A better structure to store the ingredients for a recipe is with a set. With such a structure your recipes would look like this:
recipes: {
-R1: {
name: 'Omelette',
ingredients: {
"-I1": true
}
}
}
And you can easily add a new ingredient to the recipe with:
recipe.update({ "ingredients/-I2": true });