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Model Many-to-Many Relationships with Embedded Documents

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  • About this Task
  • Example
  • Embedded Document Pattern
  • Learn More

Create a data model that uses embedded documents to describe a many-to-many relationship between connected data. Embedding connected data in a single document can reduce the number of read operations required to obtain data. In general, structure your schema so your application receives all of its required information in a single read operation. For example, you can use the embedded many-to-many model to describe the following relationships:

  • Students to classes

  • Actors to movies

  • Doctors to patients

The following example schema contains information regarding book one and book two and their authors. You can represent the relationship differently based on whether you anticipate application users querying by book or by author.

If you expect more users to query by book than by author, the example schema is an effective choice. However, if you expect more queries by author, make the author the top-level information and place the author's books in an embedded field.

You can use a many-to-many relationship to describe books and authors. A book can have multiple authors, and an author can write multiple books.

The application needs to display information for the book and author objects on a single page. To allow your application to retrieve all necessary information with a single query, embed author information inside of the corresponding book document:

{
_id: "book001",
title: "Cell Biology",
authors: [
{
author_id: "author124",
name: "Ellie Smith"
},
{
author_id: "author381",
name: "John Palmer"
}
]
}
{
_id: "book002",
title: "Organic Chemistry",
authors: [
{
author_id: "author290",
name: "Jane James"
},
{
author_id: "author381",
name: "John Palmer"
}
]
}
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