MongoDB: How to create/drop a collection (with examples)

Introduction

MongoDB, the popular NoSQL database, features a flexible schema that allows you to work without having to predefine the structure of your data. Collections in MongoDB are analogous to tables in relational databases and are a critical concept to understand when working with MongoDB.

In this tutorial, we’ll go through the steps of creating and dropping collections in MongoDB, complete with examples. We will progress from basic operations to more advanced options, providing you with a solid foundation in managing collections in MongoDB.

Prerequisites

• MongoDB server installed and running.
• Basic understanding of MongoDB commands and operations.
• MongoDB shell or a MongoDB GUI Client for executing commands.

Creating a Collection

To create a collection in MongoDB, you have two main approaches:

1. Implicit Creation
2. Explicit Creation

Implicit Collection Creation

You can create a collection implicitly by inserting a document into what you intend to be a new collection. MongoDB will automatically create the collection if it does not yet exist.

db.createCollection("inventory")

Output:

{ "ok": 1 }

Explicit Collection Creation

If you need to set specific options on your collection like capped size or validation rules, you’ll need to create it explicitly using the createCollection command.

db.createCollection("inventory", {capped: true, size: 1024, max: 5})

Output:

{ "ok": 1 }

Dropping a Collection

When you no longer need a collection, you can remove it entirely from the database using the drop command. This action is irreversible.

db.inventory.drop()

Output:

true

Working with Capped Collections

Capped collections are fixed-size collections that support high-performance reads and writes. They maintain the insertion order and, once the specified size is reached, old data is overwritten.

Creating a Capped Collection

db.createCollection("log", {capped: true, size: 100000})

Output:

{ "ok": 1 }

Converting a Collection to Capped

You can convert an existing collection to a capped collection using the convertToCapped command.

db.runCommand({convertToCapped: "messages", size: 100000})

Output:

{ "ok": 1 }

Using Validation Rules

MongoDB allows you to enforce document structure using validation rules when creating a new collection.

Creating a Collection with Validation Rules

db.createCollection("orders", {
  validator: {
    $jsonSchema: {
      bsonType: "object",
      required: ["product_id", "quantity"],
      properties: {
        product_id: {
          bsonType: "int",
          description: "must be an integer and is required"
        },
        quantity: {
          bsonType: "int",
          minimum: 0,
          description: "must be an integer greater than 0 and is required"
        }
      }
    }
  }
})

Output:

{ "ok": 1 }

Index Management

Collections house your data but use indexes to facilitate quick search. After creating your collections, it is usual to create, modify, or remove indexes to improve search performance.

Creating an Index

db.inventory.createIndex({ item: 1 })

Output:

{ "createdCollectionAutomatically": false, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1 }

Dropping an Index

db.inventory.dropIndex("item_1")

Output:

{ "nIndexesWas": 2, "ok": 1 }

Conclusion

Throughout this tutorial, you’ve learned how to manage collections in MongoDB, which included creating, dropping, and customizing collections with various options such as capped settings and validation rules. Understanding collections is fundamental when designing and working with a MongoDB database.