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Referencing Documents

MongoDB, a popular NoSQL database, supports both denormalized (embedded) and normalized (reference) data models. In this tutorial, we will focus on the reference model, which involves storing the relationship information between data by including links or references from one document to another.

What is Referencing?​

Referencing in MongoDB is a way to create relationships between documents. This is similar to how relationships are formed in relational databases. A reference from one document to another is essentially an inclusion of an ObjectID from one document within another.

When to Use Referencing?​

Referencing is useful in scenarios where:

  • The size of the data is large.
  • The data needs to remain unaltered.
  • The data is frequently updated or added to.

How to Use Referencing?​

Let's take an example of a blog application, where there is a one-to-many relationship between authors and posts. Each author can write many posts, but each post is written by only one author.

Create References​

First, we'll create documents for the authors:

var author1 = { name: "John Doe" };
db.authors.insert(author1);

Once the author document is created, MongoDB will automatically generate an _id field, which is a unique identifier for the document.

Next, we'll create a post and reference the author in the post:

var post1 = { 
    title: "MongoDB Tutorial", 
    content: "This is a MongoDB tutorial...",
    author_id: author1._id 
};
db.posts.insert(post1);

In the post document, author_id is a reference to the author document.

Query References​

To query the referenced documents, we first find the post, then use the author_id to find the author:

var post = db.posts.findOne({ title: "MongoDB Tutorial" });
var author = db.authors.findOne({ _id: post.author_id });

Advantages and Disadvantages​

Referencing documents in MongoDB offers several advantages:

  • It allows you to create complex, interrelated data structures.
  • It saves space, as you don't have to duplicate data.
  • Updates to the referenced document are automatically reflected in all documents that reference it.

However, there are also some disadvantages:

  • It can be slower to retrieve data, as you have to perform multiple queries.
  • It can be more complex to manage, as you have to manually maintain the references.

Conclusion​

In this tutorial, we have covered the concept of referencing in MongoDB, including when to use it, how to create and query references, as well as its advantages and disadvantages. By understanding and utilizing referencing, you can create more efficient and effective data models in MongoDB.