Adding indexes in mogodb - mongodb

Question

I currently have a mongodb database which is pretty unstructured. I am attempting to extract all the followers of a given set of profiles on twitter. My database looks like this:
{'123':1
'123':2
'123':3
'567':8
'567':9
}
Where each key is a user and the value is a single follower. When I attempt to create an index on these keys, I simply run out of the available index as I have a lot of users (8 million). After googling, I find that the maximum number of indexes I can have is about 64. How do I create a proper indexing on this database? OR would you suggest a different way for me to store my data?

Answer 1

You should structure your data differently.
I would recommend you to have a collection of "user" documents, where every user has an array "followers". This array should be filled with unique identifiers of the users who follow (like name, _id or your own ID number).
{ name: "userA",
followers: [
"userB",
"userC"
]
},
{ name: "userB",
followers: [
"userD",
"userF"
]
},
You can then create an index on the followers field to quickly find all users who follow an other user. When you want to find all users who follow the users "userX", "userY" and "userZ", you would then do it with this query:
db.users.find({followers: { $all: ["userX", "userY", "userZ" ] } });
Edit:
To add a follower to a user, use the $push operator:
db.users.update({name:"userA"}, { $push: { followers: "userB" } } );
The $pull operator can be used to remove array enries:
db.users.update({name:"userA"}, { $pull: { followers: "userB" } } );