Why does mgo not return the ID of inserted document?

mongodb go mgo
Sebastián Grignoli picture Sebastián Grignoli · Aug 17, 2012 · Viewed 14.1k times · Source

According to the documentation (http://godoc.org/launchpad.net/mgo/v2) you can obtain the ID of your "Upserted" document if you use the Upsert method.

There is also an Insert method that does not provide this functionality.
Why is that? What if I want to perform an Insert instead of an Upsert? (or wouldn't ever be any valid reason to want to do that? I'm starting to wonder.)

Answer

thwd picture thwd · Aug 17, 2012

You use bson.NewObjectId() to generate an ID to be inserted.

This is how you'd insert a new document:

i := bson.NewObjectId()
c.Insert(bson.M{"_id": i, "foo": "bar"})

Since you don't know if you're going to insert or update when you issue an Upsert, it would be superfluous to generate an ID just to drop it right after the query (in case an update happens). That's why it's generated db-side and returned to you when applicable.

Related questions

server returned error on SASL authentication step: Authentication failed

The following is my MongoDB connection dial from GoLang. But it's returning a panic "server returned error on SASL authentication step: Authentication failed.". My username, password, hostAddrs and dbName are correct. What am I missing here? dbName: = os.Getenv("ENV_…

Read More
How do you select all records from a mongodb collection in golang using mgo

In MongoDB doing something like db.mycollection.find() returns all documents in a collection. When working in GoLang using the package labix.org/v2/mgo and I do for example: query := db.C("client").Find(); It complains that it requires …

Read More
Golang/mgo: How can I ask MongoDB to use current time in a field?

I have this struct that matches the types of a MongoDB collection I'm using: type AppInstance struct { Id bson.ObjectId "_id,omitempty" Url string Priority int LastSeen string } I want the LastSeen field to hold the time of the last …

Read More