Spring MongoDB _id field mapping conventions

Java Spring MongoDB  : '_id' field mapping :

MongoDB requires that you have an '_id' field for all documents. If you don’t provide one the driver will assign a ObjectId with a generated value. The "_id" field can be of any type the, other than arrays.

The following outlines what field will be mapped to the '_id' document field:

• A field annotated with @Id (org.springframework.data.annotation.Id) will be mapped to the '_id' field.
  
• A field without an annotation but named 'id' will be mapped to the '_id' field.
  
• The default field name for identifiers is '_id' and can be customized via the @Field annotation.
  

Examples for the translation of '_id'-field definitions

Field definition	Resulting Id-Fieldname in MongoDB
String id	_id
@Field String id	_id
@Field('x') String id	x
@Id String x	_id
@Field('x') @Id String x	_id

Source :  How the '_id' field is handled in the mapping layer

MongoDB Multiple insert at once

We can insert multiple documents (bulk insert) to a collection using a single insert command :

Syntax :
   db.[COLLECTION].insert( [ { DOC1 }, {DOC2} ] ) ;

Example :
   db.people.insert( [ {name: "Ganesh", age: 24, country : "Nepal"}, {name: "John", age : 20} ]);

In Java  ( Using Spring Data JPA Repository )

   personRepository.insert( personList);
   --> It follows org.springframework.data.mongodb.repository.MongoRepository#insert(Iterable<S> entities) method's syntax

MongoDB rename a database

As of now, there is not a straight forward way to rename a MongoDB database. But you can use the following steps to achieve so :

Here, we are trying to rename OLD_DB to NEW_DB

Steps :
1) copy old database to new one using db.CopyDatabase( OLD_DB, NEW_DB )
2) switching to OLD_DB and dropping the database

Mongo Command :

  #Step 1 : Copy database to new name
     db.copyDatabase("OLD_DB","NEW_DB") 

  #Step 2 and 3, drop OLD_DB
     use OLD_DB
     db.dropDatabase()