Mongodb avoid duplicate entries

Question

I am newbie to mongodb. May I know how to avoid duplicate entries. In relational tables, we use primary key to avoid it. May I know how to specify it in Mongodb using java?<

Answer 1

I am not a Java programmer however you can probably convert this over.

MongoDB by default does have a primary key known as the _id you can use upsert() or save() on this key to prevent the document from being written twice like so:

var doc = {'name': 'sam'};
db.users.insert(doc); // doc will get an _id assigned to it
db.users.insert(doc); // Will fail since it already exists

This will stop immediately duplicates. As to multithread safe inserts under certain conditions: well, we would need to know more about your condition in that case.

I should add however that the _id index is unqiue by default.