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I am developing an API using Codeigniter and MongoDB. In this system I am saving the full name and _ID of users that the selected user is following.
What is best to do regarding the _Id? Store it as an object or as a string? If I store it as an object I need to convert it to string when echoing out followers otherwise the output looks strange.
My question is really. Is it ok to store the _Id as a string rather than an object? What is the downside of storing as string?
Thankful for all input!
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Yes, you can use a string as your _id.
Architecturally, by default the _id field is an ObjectID, one of MongoDB's BSON types. The ObjectID is the primary key for the stored document and is automatically generated when creating a new document in a collection.
The _id is the default key that is generated to uniquely identify each document in the collection. The 12-byte ObjectId, which is a hexadecimal string value consists of: a 4-byte value representing the seconds since the Unix epoch, a 3-byte machine identifier, a 2-byte process id, and.
You should NOT convert the ObjectId in the database to a string, and then compare it to another string. If you'd do this, MongoDB cannot use the _id index and it'll have to scan all the documents, resulting in poor query performance.
Performance for requests (and updates) are really better with objectid. More over, objectid are quite small in space.
From the official doc :
BSON includes a binary data datatype for storing byte arrays. Using this will make the id values, and their respective keys in the _id index, twice as small.
here are 2 links that can help you : - http://www.mongodb.org/display/DOCS/Optimizing+Object+IDs - http://www.mongodb.org/display/DOCS/Object+IDs
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