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name Punditsdkoslkdosdkoskdo

Difference between set with {merge: true} and update

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.

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:

  {a: {b: {c: true}}},
  {merge: true}

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

  'a.b.c': true
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