In this section, we will cover how to delete documents in MongoDB. Deleting documents is a crucial operation when managing data, as it allows you to remove outdated or unnecessary information from your database. We will explore different methods to delete documents, including deleting a single document and deleting multiple documents.

1. Delete Operations: MongoDB provides two primary methods for deleting documents:

   • deleteOne(): Deletes a single document that matches the specified filter.
   • deleteMany(): Deletes all documents that match the specified filter.

2. Filters: Filters are used to specify the criteria for selecting documents to delete. Filters can be simple or complex, depending on the requirements.

3. Write Concern: Write concern specifies the level of acknowledgment requested from MongoDB for write operations. It can be configured to ensure data integrity during delete operations.

The deleteOne() method is used to delete a single document that matches the specified filter. If multiple documents match the filter, only the first matching document will be deleted.

• filter: A document that specifies the criteria for the deletion.
• options (optional): Additional options for the delete operation.

Let's assume we have a collection named users with the following documents:

To delete the document where the name is "Bob":

After executing the above command, the users collection will look like this:

The deleteMany() method is used to delete all documents that match the specified filter.

• filter: A document that specifies the criteria for the deletion.
• options (optional): Additional options for the delete operation.

To delete all documents where the age is greater than 25:

After executing the above command, the users collection will look like this:

1. Insert the following documents into a collection named products:

   [
     { "_id": 1, "product": "Laptop", "price": 1000 },
     { "_id": 2, "product": "Phone", "price": 500 },
     { "_id": 3, "product": "Tablet", "price": 300 }
   ]
   

2. Write a command to delete the document where the product is "Phone".

1. Insert the following documents into a collection named orders:

   [
     { "_id": 1, "order_id": "A001", "status": "shipped" },
     { "_id": 2, "order_id": "A002", "status": "pending" },
     { "_id": 3, "order_id": "A003", "status": "shipped" },
     { "_id": 4, "order_id": "A004", "status": "pending" }
   ]
   

2. Write a command to delete all documents where the status is "pending".

• Accidental Deletion: Be cautious with your filters to avoid accidentally deleting more documents than intended. Always double-check your filter criteria.
• Backup: Before performing delete operations, consider backing up your data to prevent data loss.
• Testing: Test your delete operations in a development environment before applying them to production data.

In this section, we learned how to delete documents in MongoDB using the deleteOne() and deleteMany() methods. We also explored practical examples and exercises to reinforce the concepts. Deleting documents is a fundamental operation in MongoDB, and understanding how to use it effectively is crucial for managing your data. In the next section, we will dive into data modeling in MongoDB, starting with schema design.