Difference between set with {merge: true} and update

Question

In Cloud Firestore there are three write operations:

1) add

2) set

3) update

In the docs it says that using set(object, {merge: true}) will merge object with existing one.

The same happens when you use update(object) So what is the difference if any? It seems strange that google will duplicate logic.

Answer 1

The way I understood the difference:

• set without merge will overwrite a document or create it if it doesn't exist yet

• set with merge will update fields in the document or create it if it doesn't exists

• update will update fields but will fail if the document doesn't exist

• create will create the document but fail if the document already exists

There's also a difference in the kind of data you provide to set and update.

For set you always have to provide document-shaped data:

set(
  {a: {b: {c: true}}},
  {merge: true}
)

With update you can also use field paths for updating nested values:

update({
  'a.b.c': true
})