Creating Documents in MongoDB

In MongoDB, documents are the basic unit of data storage, similar to a row in a relational database. A document is a JSON-like object (stored as BSON in MongoDB) that consists of key-value pairs. You can create and insert documents into a collection, which is a group of related documents within a database.

Steps to Create a Document in MongoDB

1. Select a Database: First, switch to the database where you want to create the document. If the database doesn’t exist, MongoDB will create it automatically when you insert a document into a collection.

   use myDatabase
   

2. Choose or Create a Collection: MongoDB collections are like tables in relational databases. You can insert a document into an existing collection, or if the collection doesn’t exist, MongoDB will create it on the fly when you insert a document.

3. Insert a Document: You can insert documents using the insertOne(), insertMany(), or other methods, depending on how many documents you want to create.

Methods for Creating Documents

1. insertOne(): Insert a Single Document

This method allows you to insert a single document into a collection.

db.collection.insertOne(document)

• collection: The name of the collection where you want to insert the document.
• document: The document to be inserted.

Example:

db.users.insertOne({
  name: "John Doe",
  age: 28,
  email: "johndoe@example.com",
  created_at: new Date()
})

This creates a new user document in the users collection with fields like name, age, email, and created_at. If the users collection does not already exist, MongoDB will create it.

2. insertMany(): Insert Multiple Documents

To insert multiple documents at once, use the insertMany() method.

db.collection.insertMany([document1, document2, ...])

Example:

db.products.insertMany([
  { name: "Laptop", price: 899.99, in_stock: true },
  { name: "Smartphone", price: 699.99, in_stock: false }
])

This inserts two documents into the products collection, representing a laptop and a smartphone.

Document Structure

MongoDB documents are made up of key-value pairs. Each key is a string, and the value can be any valid BSON data type, such as:

• String: "John Doe"
• Number: 28
• Boolean: true/false
• Date: new Date() (JavaScript's date object)
• Array: [88, 92, 79] (a list of values)
• Object (embedded document): { city: "New York", state: "NY" }
• ObjectId: A unique 12-byte identifier, often used in the _id field to uniquely identify each document.

Here’s an example of a more complex document with various data types:

db.orders.insertOne({
  customer: {
    name: "Alice Smith",
    email: "alice@example.com"
  },
  items: [
    { product: "Laptop", quantity: 1, price: 899.99 },
    { product: "Mouse", quantity: 2, price: 19.99 }
  ],
  order_date: new Date(),
  status: "shipped"
})

Auto-generated _id Field

When inserting a document, if you do not explicitly provide an _id field, MongoDB will automatically generate one. The _id field is a unique identifier for each document in a collection.

{
  _id: ObjectId("5f47df78bdbbfcf7b6a9e0d1"),
  name: "John Doe",
  age: 28,
  email: "johndoe@example.com"
}

The _id is usually of the ObjectId data type, but you can also manually assign a different value (e.g., string, integer) to the _id field if needed.

Example:

db.customers.insertOne({
  _id: "customer123",
  name: "Charlie Brown",
  email: "charlie@example.com"
})

In this case, the _id is manually set to "customer123".

Upserting Documents

MongoDB supports an "upsert" operation, which is a combination of "update" and "insert". If a document matching the query exists, it will be updated; if not, a new document will be created.

Example of upsert:

db.users.updateOne(
  { email: "johndoe@example.com" },  // Query
  { $set: { name: "John Doe", age: 28 } },  // Update
  { upsert: true }  // Upsert option
)

If no document with email: "johndoe@example.com" exists, MongoDB will insert a new document with the specified values.

Insert Performance Considerations

• Bulk Inserts: Using insertMany() can improve performance when inserting multiple documents, as it reduces the number of write operations.
• Write Concerns: MongoDB allows you to specify the level of acknowledgment from the database when inserting a document. For example, you can ensure the write is acknowledged by the majority of the replica set members for greater data safety.