How to stop insertion of Duplicate documents in a mongodb collection

Question

Let us have a MongoDB collection which has three docs..

db.collection.find()

 { _id:'...', user: 'A', title: 'Physics',   Bank: 'Bank_A' }  { _id:'...', user: 'A', title: 'Chemistry', Bank: 'Bank_B' }  { _id:'...', user: 'B', title: 'Chemistry', Bank: 'Bank_A' } 

We have a doc,

 doc = { user: 'B', title: 'Chemistry', Bank:'Bank_A' } 

If we use

 db.collection.insert(doc)  

here, this duplicate doc will get inserted in database.

 { _id:'...', user: 'A', title: 'Physics',   Bank: 'Bank_A' }  { _id:'...', user: 'A', title: 'Chemistry', Bank: 'Bank_B' }  { _id:'...', user: 'B', title: 'Chemistry', Bank: 'Bank_A' }  { _id:'...', user: 'B', title: 'Chemistry', Bank: 'Bank_A' } 

How this duplicate can be stopped. On which field should indexing be done or any other approach?

Answer 1

Don't use insert.

Use update with upsert=true. Update will look for the document that matches your query, then it will modify the fields you want and then, you can tell it upsert:True if you want to insert if no document matches your query.

db.collection.update(    <query>,    <update>,   {     upsert: <boolean>,      multi: <boolean>,     writeConcern: <document>    }   ) 

So, for your example, you could use something like this:

db.collection.update(doc, doc, {upsert:true})