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:

{:,:,:}

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"  span class= "str" > "$db" :  "W3CSCHOOLCC" },< Span class= "PLN" >  "contact" :  "987654321" Span class= "pun" >,  "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.. Findone ({ "name" : "Tom Benzamin" >var Dbref = User.>db[dbref $ref findone ({:( Dbref. $id               

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

{   "_ID" : objectid ( "534009e4d852427820000002" Span class= "pun"),   "building"  :  "A, Indiana Apt" ,  "Pincode"  : 123456, "city"  :  "Los Angeles" Span class= "pun" >,  "state"  :   "California" }       

MongoDB Database Reference