如何使用 Go 将文档 ID 作为字段值 Firestore 插入

Question

I would like to search documents with a particular ID during a Collection Group Query. From what I have read it is not possible to perform a CGQ using the document ID directly, so I intend to mirror the document's ID in a field id within the document.

I tried firestore.DocumentID (see code snippet below) expecting it to serve as a sentinel value representing the document's ID (not yet known at the time the method is called). I discovered firestore.DocumentID is a actually a const with a value of "__name__" and that becomes a string value of the id field within the resulting document.

docRef, _, err := colRef.Add(ctx, map[string]interface{}{
        "id":       firestore.DocumentID, // this does not work
        "events":   events,
        "url":      url,
        "enabled":  true,
        "created":  firestore.ServerTimestamp,
        "modified": firestore.ServerTimestamp,
})

Is it possible to write the document's ID inside the document to the id field whilst calling the Add method atomically?

If so, what is that sentinel value? If not, should I perform a transaction that first creates the document and then, in turn, updates the document with the id field?

Answer 1

You can't tell the Firestore client to insert its new ID while writing.

To get both into the database with a single write operation, you'll have to split the creation of the new DocumentReference (which is a client-side operation) from the actual writing of the data.

So two steps:

1. Create a new DocumentReference by calling colRef.NewDoc() .
2. Write the data (including the ID) into the reference withdocRef.Set() .