MongoDB Database Reference

There are two types of MongoDB references:

• Manual reference (Manual References)
• DBRefs

DBRefs vs Manual Reference

Consider a scenario in which we store different addresses (address, Office address, email address, etc.) in different collections (Address_home, Address_office, address_mailing, etc.).

This way, when we call different addresses, we also need to specify the collection, a document that references the document from multiple collections, and we should use DBRefs.

Using DBRefs

form of Dbref:

{$ref:, $id:, $db:  }

The three fields represent the meaning:

• $ref: Collection Name
• $ID: The ID of the reference
• $DB: Database name, optional parameters

The user data document in the following example uses the Dbref, field address:

{   "_id": ObjectId ("53402597d852426020000002"),   "address": {   "$ref": "Address_home",   "$id": ObjectId ("534009e4d852427820000002"),   "$db": "W3CSCHOOLCC"},   "contact": "987654321",   "DOB": " 01-01-1991 ",   " name ":" Tom benzamin "}

Address The Dbref field specifies that the referenced address document is a W3CSCHOOLCC database under the Address_home collection, with an ID of 534009e4d852427820000002.

In the following code, we look up the user address information for the specified ID in the collection by specifying the $REF parameter (Address_home collection):

>var user = Db.users.findOne ({"Name": "Tom Benzamin"}) >var dbref = user.address>db[dbref. $ref].findone ({"_id" :(dbref. $id)})

The above instance returns the address data from the Address_home collection:

{   "_id": ObjectId ("534009e4d852427820000002"),   "building": "A, Indiana Apt",   "Pincode": 123456,   ' city ': ' Los Angeles ', ' State   ': ' California '}

MongoDB Database Reference