i am new to mongodb and stack overflow.
I want to know why on mongodb collection ID is of 24 hex characters? what is importance of that?
_id
a 24 character hex string?The default unique identifier generated as the primary key (_id
) for a MongoDB document is an ObjectId. This is a 12 byte binary value which is often represented as a 24 character hex string, and one of the standard field types supported by the MongoDB BSON specification.
The 12 bytes of an ObjectId are constructed using:
ObjectIds (or similar identifiers generated according to a GUID formula) allow unique identifiers to be independently generated in a distributed system.
The ability to independently generate a unique ID becomes very important as you scale up to multiple application servers (or perhaps multiple database nodes in a sharded cluster). You do not want to have a central coordination bottleneck like a sequence counter (eg. as you might have for an auto-incrementing primary key), and you will want to insert new documents without risk that a new identifier will turn out to be a duplicate.
An ObjectId is typically generated by your MongoDB client driver, but can also be generated on the MongoDB server if your client driver or application code or haven't already added an _id
field.
No. If you have a more suitable unique identifier to use, you can always provide your own value for _id
. This can either be a single value or a composite value using multiple fields.
The main constraints on _id
values are that they have to be unique for a collection and you cannot update or remove the _id
for an existing document.