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The best MongoDB database references Tutorial In 2024, In this tutorial you can learn DBRefs vs reference manual,Use DBRefs,

MongoDB database references

In the previous section we mentioned the relationship MongoDB MongoDB reference to standardize the data structure of the document.

MongoDB has two references:

  • Reference manual (Manual References)
  • DBRefs

DBRefs vs reference manual

Consider such a scenario, we have a different set (address_home, address_office, address_mailing, etc.) stored in a different address (address, office address, mailing address, etc.).

Thus, when we call different address, you need to specify a collection, a collection of documents from multiple referenced documents, we should use DBRefs.

Use DBRefs

DBRef forms: 

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

Significance of three fields represented by:

  • $ Ref: collection name
  • $ Id: reference id
  • $ Db: database name, optional parameters

The following example uses a user data document 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 DBRef field specifies the address referenced documents are under address_home collection w3cschoolcc database, id is 534009e4d852427820000002.

The following code, we have to find the collection at the specified address information user id specified by $ ref parameter (address_home set): 

>var user = db.users.findOne({"name":"Tom Benzamin"})
>var dbRef = user.address
>db[dbRef.$ref].findOne({"_id":(dbRef.$id)})

The above examples returned address_home collection address data: 

{
   "_id" : ObjectId("534009e4d852427820000002"),
   "building" : "22 A, Indiana Apt",
   "pincode" : 123456,
   "city" : "Los Angeles",
   "state" : "California"
}

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MongoDB database references
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