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

In mongodb _id field is reserved for primary key. Mongodb use an internal ObjectId value if you don't define it in your object and also create an index to ensure performance.

But you can put your own unique value for _id and Mongodb will use it instead of making one for you. And even if you want to use multiple field as primary key you can use an object:

{ _id : { a : 1, b: 1} }

Just be careful when creating these ids that the order of keys (a and b in the example) matters, if you swap them around, it is considered a different object.