How to set a primary key in MongoDB?

Question

I want to set one of my fields as primary key. I am using MongoDB as my NoSQL.

Answer 1

This is the syntax of creating primary key

db.< collection >.createIndex( < key and index type specification>, { unique: true } )

Let's take that our database have collection named student and it's document have key named student_id which we need to make a primary key. Then the command should be like below.

db.student.createIndex({student_id:1},{unique:true})

You can check whether this student_id set as primary key by trying to add duplicate value to the student collection.

prefer this document for further informations https://docs.mongodb.com/manual/core/index-unique/#create-a-unique-index

Answer 2

Simple you can use

db.collectionName.createIndex({urfield:1},{unique:true});

Answer 3

_id field is reserved for primary key in mongodb, and that should be a unique value. If you don't set anything to _id it will automatically fill it with "MongoDB Id Object". But you can put any unique info into that field.

Additional info: http://www.mongodb.org/display/DOCS/BSON

Hope it helps.