MongoDB - Embedded Documents

MongoDB provides you a cool feature which is known as Embedded or Nested Document. Embedded document or nested documents are those types of documents which contain a document inside another document. Or in other words, when a collection has a document, this document contains another document, another document contains another sub-document, and so on, then such types of documents are known as embedded/nested documents. 

Notes - In MongoDB, you can only nest document up to 100 levels. The overall document size must not exceed 16 MB.

Creating Embedded Documents -

In MongoDB, you can easily embed a document inside another document. As we know that in the mongo shell, documents are represented using curly braces ( {} ) and inside these curly braces we have field-value pairs. Now inside these fields, we can embed another document using curly braces {} and this document may contain field-value pairs or another sub-document. 

Syntax: 

{
....
field: {field1: value1, field2: value2}
....
}

Let us discuss this concept with the help of the given examples - 
Example 1: 
Suppose we have a database named 'GeeksforGeeks'. Now this database has a collection named 'Courses' and this collection contains a document. Inside this document, we have a field named 'name' which contains another document and this document contain three fields(i.e, first, middle, last) with their values.  

Example 2: 
Again, we are taking GeeksforGeeks database. Inside this database, we already have a collection named 'Courses', now we add another document in this collection, which contains the details of the student who select paid courses. Inside this document, we have a field named 'courseDetails'. This field contains a document and this document contains some field-value pairs and a sub-document which contains the paymentDetials. 

So, overall the Courses collection contains two documents and these documents contain nested documents.