The difference between installing with {merge: true} and updating

Question

Cloud Firestore has three write operations:

1) add

2) install

3) update

The docs say that using set(object, {merge: true}) will merge the object with the existing one.

The same thing happens when using update(object) So what's the difference, if any? It seems strange that google will duplicate the logic.

Answer 1

As I understand the difference:

• set without merging will overwrite the document or create it if it does not already exist

• set with merge will update fields in the document or create it if it does not exist

• update will update the fields, but will not work if the document does not exist

• create will create the document but will not work if the document already exists

There is also a difference in the kind of data that you provide set and update .

For set you always need to provide data in the form of a document:

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

With update you can also use field paths to update nested values:

 update({ 'abc': true }) 

Answer 2

Another difference (extension of Scarygami's answer) between "set with merge" and "update" is work with nested values.

if you have a document structured as follows:

  { "friends": { "friend-uid-1": true, "friend-uid-2": true, } } 

and want to add {"friend-uid-3" : true}

using this:

db.collection('users').doc('random-id').set({ "friends": { "friend-uid-3": true } },{merge:true})

will result in the following data:

  { "friends": { "friend-uid-1": true, "friend-uid-2": true, "friend-uid-3": true } } 

however update using this:

db.collection('users').doc('random-id').update({ "friends": { "friend-uid-3": true } })

will result in the following data:

  `{ "friends": { "friend-uid-3": true } }`