Avoid duplicate values and create composite primary key

[Balaji D]

Hi,

I am trying to insert json object in mongoDB. How can I ensure I am
not inserting duplicate record. MongoDb by itself creates a unique id.
If I want to restrict duplicate calues based on two columns (composite
primary key), how should I proceed with that.

regards,
Balaji D.

[Martin Skøtt]

Most straightforward way is to create a unique index on the two properties - just like you would do in a RDBMS.

Martin 

[Sam Millman]

You can create a unique compound index like so:

db.col.ensureIndex({'_id':1, 'somefield': 1}, {'unique': true})

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[Derick Rethans]

You will need to set a unique index on those field, for example with:

db.yourcollection.ensureIndex( { fieldname1: 1, fieldname2: 1 }, { unique: true } );

you can find some more information at
http://www.mongodb.org/display/DOCS/Indexes#Indexes-unique%3Atrue

cheers,
Derick

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