Question

I am using MonoDB as a databse…….

I am going to generate a _id for each document for
that i use useId and FolderID for that user

here userId is different for each User and also Each user has different FolderIds

i generate _id as

userId="user1"
folderId="Folder1"

_id = userId+folderId

is there any effect of this id generation on mongoDB Indexing…
will it work Fast like _id generated by MongoDB

Answer 1

A much better solution would be to leave the _id column as it is and have separate userId and folderId fields in your document, or create a separate field with them both combined.

As for if it will be “as fast” … depends on your query, but for ordering by “create” date of the document for example you’d lose the ability to simply order by the _id you’d also lose the benefits for sharding and distribution.

However if you want to use both those ID’s for your _id there is one other option …

You can actually use both but leave them separate … for example this is a valid _id:

> var doc = { "_id" : { "userID" : 12345, "folderID" : 5152 }, 
              "field1" : "test", "field2" : "foo" };
> db.crazy.save(doc);
> db.crazy.findOne();
{
        "_id" : {
                "userID" : 12345,
                "folderID" : 5152
        },
        "field1" : "test",
        "field2" : "foo"
}
>