How do you create a relationship between collections in MongoDB?

How do you create a relationship between collections in MongoDB?

Relationships in MongoDB represent how various documents are logically related to each other. Relationships can be modeled via Embedded and Referenced approaches. Such relationships can be either 1:1, 1:N, N:1 or N:N. Let us consider the case of storing addresses for users.

How do I link two documents in MongoDB?

MongoDB applications use one of two methods for relating documents:

1. Manual references where you save the _id field of one document in another document as a reference.
2. DBRefs are references from one document to another using the value of the first document’s _id field, collection name, and, optionally, its database name.

How are relationships implemented in MongoDB?

In MongoDB, a relationship represents how different types of documents are logically related to each other. Relationships like one-to-one, one-to-many, etc., can be represented by using two different models: Embedded document model. Reference model.

What is the difference between a document and a collection in MongoDB?

In MongoDB, documents are stored in a collection, which in turn make up a database. Document are analogous to rows in a SQL table, but there is one big difference: not every document needs to have the same structure—each of them can have different fields and that is a very useful feature in many situations.

Is MongoDB good for relationships?

Document databases such as MongoDB are sometimes called “schema-less” due to the fact that they don’t really enforce relationships like RDBMSes do. In fact, MongoDB allows relationships between documents to be modeled via Embedded and Referenced approaches.

What does a MongoDB collection consists of?

A document is a representation of a single entity of data in the MongoDB database. A collection consists of one or more related objects. A major difference exists between MongoDB and SQL, in that documents are different from rows. Row data is flat, with one column for each value in the row.

Which field is always the first field in the document?

_id field
Document Field Order The _id field is always the first field in the document.

How is a relationship represented in MongoDB?

In MongoDB, a relationship represents how different types of documents are logically related to each other. Relationships like one-to-one, one-to-many, etc., can be represented by using two different models: Embedded Document Model: In this model, the documents are embedded inside one document.

How does the embedded approach work in MongoDB?

In the embedded approach, we will embed the address document inside the user document. This approach maintains all the related data in a single document, which makes it easy to retrieve and maintain. The whole document can be retrieved in a single query such as −

How can I get address details from MongoDB?

Using these ObjectIds, we can query the address documents and get address details from there. With this approach, we will need two queries: first to fetch the address_ids fields from user document and second to fetch these addresses from address collection.

How to avoid repetition of publisher Data in MongoDB?

To avoid repetition of the publisher data, use references and keep the publisher information in a separate collection from the book collection. When using references, the growth of the relationships determine where to store the reference.