Insert documents

insertOne adds one document and insertMany adds several. Every document needs a unique _id within its collection; MongoDB can generate one when it is omitted.

In MongoDB, inserting data means adding new documents to a collection. You don't need to predefine the schema or structure of your data, making it flexible and fast to use. MongoDB provides two main methods for insert operations:

• insertOne() – inserts a single document
• insertMany() – inserts multiple documents at once

Before working through the examples, make sure you can connect with mongosh and select your database. Use a practice database for writes and deletions.

This method is used to insert a single document into a collection. If the collection doesn’t exist yet, MongoDB will automatically create it for you.

Step-by-step:

1. Start the MongoDB shell
2. Select or create your database
3. Use insertOne() to insert a document

Example 1: Insert One User Document

    mongo

    use mydb
    db.users.insertOne({
      name: "Alice",
      age: 25,
      email: "alice@example.com"
    });

    {
      acknowledged: true,
      insertedId: ObjectId("...")
    }

Explanation: The document is inserted into the users collection. MongoDB auto-generates a unique _id field for each document if not provided.

Intuition Check

Q: What happens if the users collection doesn't exist yet?

A: MongoDB will automatically create the collection when you insert the first document. You don’t need to explicitly create it beforehand.

This method is used to insert multiple documents into a collection in one operation. It's more efficient than calling insertOne() multiple times.

Example 2: Insert Multiple Product Documents

    db.products.insertMany([
      {
        name: "Laptop",
        brand: "Dell",
        price: 70000
      },
      {
        name: "Phone",
        brand: "Samsung",
        price: 30000
      },
      {
        name: "Tablet",
        brand: "Apple",
        price: 50000
      }
    ]);

    {
      acknowledged: true,
      insertedIds: {
        "0": ObjectId("..."),
        "1": ObjectId("..."),
        "2": ObjectId("...")
      }
    }

Explanation: Each document in the array is inserted into the products collection. The insertedIds map shows the index and ID of each inserted document.

Intuition Check

Q: Can documents inserted with insertMany() have different fields?

A: Yes! MongoDB allows documents with different fields in the same collection. It doesn’t enforce a fixed schema.

You can also specify your own _id field if you want full control over the document identifier.

Example 3: Insert Document with Custom _id

    db.users.insertOne({
      _id: "user123",
      name: "Bob",
      age: 28
    });

    {
      acknowledged: true,
      insertedId: "user123"
    }

Explanation: The document uses a custom string _id instead of the default ObjectId. This can be useful when integrating with external systems that use predefined IDs.

Intuition Check

Q: What happens if you insert another document with the same _id?

A: MongoDB will throw a duplicate key error. The _id must be unique within the collection.

insertOne adds one document and insertMany adds several. Every document needs a unique _id within its collection; MongoDB can generate one when it is omitted.

Summary

• insertOne() adds a single document
• insertMany() adds multiple documents efficiently
• If the collection doesn’t exist, MongoDB creates it automatically
• You can use custom _id values, but they must be unique

In the next topic, we will learn how to read documents from the collection using powerful querying features like find() and filters.

• Build precise query filters