MongoDB Relationships and database references

MongoDB Relationship:

MongoDB relationships represent the logical interconnectedness of multiple documents. Links can be established between documents through embedding and referencing.

1. Embedding Relationship:

Form: Embed a document in another document.

Pros: Data is stored in a single document, which makes it easier to get and maintain data. (One-time query only)

Disadvantage: If the amount of data is constantly increasing, it will affect read and write performance.

Examples of Use:

{

"_id": ObjectId ("52ffc33cd85242f436000001"),

"Name": "Tom benzamin",

"Address": [

{

"Building": "A, Indiana Apt",

"Pincode": 123456,

},

{

"Building": "A, Acropolis Apt",

"Pincode": 456789,

}]

}

Query Example:

Db.users.findOne ({"Name": "Tom benzamin"},{"Address": 1})

2. Citation relationship:

Form: Establishes a relationship through the ID field of the document .

Cons: Queries are required two times.

Examples of Use:

{

"_id": ObjectId ("52ffc33cd85242f436000001"),

"Name": "Tom benzamin",

"Address_ids": [

ObjectId ("52ffc4a5d85242602e000000"),

ObjectId ("52ffc4a5d85242602e000001")

]

}

Query Example:

>var result = Db.users.findOne ({"Name": "Tom benzamin"},{"Address_ids": 1})

>var addresses = Db.address.find ({"_id": {"$in": result["Address_ids"]}})

Database reference: You should use DBRefswhen a document needs to refer to a document from multiple collections.

form of DBRefs:

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

The three fields represent the meaning:

$ref: Collection name

$id: The ID of the reference

$DB: Database name, optional parameters

Examples of Use:

{

"_id": ObjectId ("53402597d852426020000002"),

"Address": {

"$ref": "Address_home",

"$id": ObjectId ("534009e4d852427820000002"),

"$db": "W3CSCHOOLCC"},

"Contact": "987654321",

"DOB": "01-01-1991",

"Name": "Tom benzamin"

}

Query Example:

>var user = Db.users.findOne ({"Name": "Tom Benzamin"})

>var Dbref = user.address

>db[dbref. $ref].findone ({"_id":(dbref. $id)})

MongoDB Relationships and database references