Model One-to-Many Relationships with Embedded Documents

Create a data model that uses embedded documents to describe a one-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 the embedded one-to-many model to describe the following relationships:

Country to major cities
Author to books
Student to classes

Example

The example schema contains three entities, with address one and address two belonging to the same patron:

// patron document
{
   _id: "joe",
   name: "Joe Bookreader"
}
// address one
{
   street: "123 Fake Street",
   city: "Faketon",
   state: "MA",
   zip: "12345"
}
// address two
{
   street: "1 Some Other Street",
   city: "Boston",
   state: "MA",
   zip: "12345"
}

Embedded Document Pattern

In this example the application needs to display information for the patron and both address objects on a single page. To allow your application to retrieve all necessary information with a single query, embed the address one and address two information inside of the patron document:

{
   _id: "joe",
   name: "Joe Bookreader",
   addresses: [
      {
         street: "123 Fake Street",
         city: "Faketon",
         state: "MA",
         zip: "12345"
      },
      {
         street: "1 Some Other Street",
         city: "Boston",
         state: "MA",
         zip: "12345"
      }
   ]
 }

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One-to-One Embedded Documents

One-to-Many References