Introduction

This section explains how to insert a single document into a MongoDB collection using the insertOne() method. We'll cover the structure of a document, the syntax of insertOne(), and the structure of the return value.

Understanding Documents in MongoDB

In MongoDB, data is stored in documents. A document is a set of field-value pairs. Documents are analogous to rows in relational database tables, but with the flexibility of schemaless data. Documents are stored in collections.

Structure of a Document

Documents are JSON-like structures (BSON – Binary JSON) consisting of fields and values. A field can hold different data types, including:

• String
• Number (Integer, Double, Decimal)
• Boolean
• Date
• Array
• Embedded Document (nested document)
• ObjectId (a unique identifier)

Example of a document:

 {
    "name": "John Doe",
    "age": 30,
    "city": "New York",
    "is_active": true,
    "hobbies": ["reading", "hiking", "coding"],
    "address": {
        "street": "123 Main St",
        "zip": "10001"
    }
} 

Using the insertOne() Method

The insertOne() method is used to insert a single document into a collection. The syntax is as follows:

 db.collectionName.insertOne(document, options) 

• db: Refers to the current database.
• collectionName: The name of the collection where you want to insert the document.
• document: The document to insert. This is a JSON-like object.
• options: (Optional) An object specifying additional options for the insertion. Common options include writeConcern and bypassDocumentValidation. We won't cover options in detail in this basic guide.

Example 1: Inserting a Simple Document

Let's insert a simple document into a collection named "users":

 db.users.insertOne(
  {
    "name": "Alice Smith",
    "age": 25,
    "city": "London"
  }
) 

Example 2: Inserting a Document with an Array

This example shows how to insert a document with an array field:

 db.products.insertOne(
  {
    "name": "Laptop",
    "price": 1200,
    "tags": ["electronics", "computer", "portable"]
  }
) 

Example 3: Inserting a Document with a Nested Document

This demonstrates inserting a document containing another document (embedded document):

 db.customers.insertOne(
  {
    "name": "Bob Johnson",
    "email": "bob.johnson@example.com",
    "address": {
      "street": "456 Oak Ave",
      "city": "Los Angeles",
      "zip": "90001"
    }
  }
) 

Example 4: Relying on MongoDB to automatically generate the _id field.

If you do not specify an _id field in your document, MongoDB will automatically generate a unique ObjectId for it. The _id field serves as the primary key for the document. It is highly recommended to let MongoDB handle the _id generation.

 db.books.insertOne(
  {
    "title": "The Hitchhiker's Guide to the Galaxy",
    "author": "Douglas Adams",
    "pages": 224
  }
) 

The Return Value of insertOne()

The insertOne() method returns an object containing information about the insertion operation. The most important property is acknowledged and insertedId.

 {
  "acknowledged" : true,
  "insertedId" : ObjectId("654398a79514d6e28b791e6f")
} 

• acknowledged: A boolean value indicating whether the write operation was acknowledged by the server. It's usually true.
• insertedId: The ObjectId of the inserted document. This is how you can uniquely identify the document you just inserted. If you specified your own _id field in the document, this value will reflect that.

Example:

 let result = db.users.insertOne({name: "Jane Doe", age: 28});
console.log(result.acknowledged); // Output: true
console.log(result.insertedId);   // Output: ObjectId("654398a79514d6e28b791e6f") (or similar) 

Important Considerations

• Data Type Consistency: While MongoDB is schemaless, it's good practice to maintain consistency in data types within a collection for ease of querying and analysis. For instance, if one document has the "age" field as a number, subsequent documents should also store "age" as a number.
• Error Handling: In a production environment, you should always wrap your insertOne() calls in a try-catch block to handle potential errors, such as network issues or write conflicts.