Question

My document has the format as show below:

{
    "_id":ObjectId("4fabcd13"),
    users:[
        {id:"001", tags:["friend", "buiz"]}, 
        {id:002, tags:["relationship"]}
    ]
},
{
    "_id":ObjectId("4fabcd14"),
    users:[
        {id:"003", tags:["buiz"]}, 
        {id:002, tags:["friend"]}
    ]
},

Can I let MongoDB index on users.tags element? I had tried the use following statement but failed:

db.invoices.ensureIndex({user.tags:1})

Thanks a lot!

Answer 1

I think you just missed the quotes (because of the dot in the field name), and the field is called “users”, not “user”:

db.invoices.ensureIndex({"users.tags":1})