1. Definition

The Referenced Data Model in MongoDB is a way of storing related data in separate documents and linking them using references (usually via ObjectId). It is also called a normalized data model.

2. When to Use

• When data is large and complex
• When relationships are one-to-many or many-to-many
• When data needs to be updated frequently
• When avoiding data duplication is important

3. Where it is Used

• E-commerce apps (users, orders, products)
• Social media platforms
• Blog systems (users and posts)
• Applications with complex relationships

4. Why We Use It

• Avoids data duplication
• Improves data consistency
• Handles large datasets efficiently
• Better for frequently updated data

5. How It Works

• Stores related data in different collections
• Uses ObjectId to create references
• Data is linked instead of embedded
• Requires multiple queries or population

Basic Syntax

// User document
{
  _id: ObjectId("user123"),
  name: "Manaswini"
}

// Order document referencing user
{
  product: "Laptop",
  userId: ObjectId("user123")
}

Real Example

// Users Collection
{
  _id: ObjectId("u1"),
  name: "Manaswini"
}

// Orders Collection
{
  product: "Phone",
  userId: ObjectId("u1")
}

6. Explanation

• Data is stored in separate collections
• Documents are linked using ObjectId
• Reduces duplication of data
• Requires joining logic in application or using populate

7. Advantages

• No data duplication
• Better data consistency
• Efficient for large datasets
• Easier to update data

8. Disadvantages

• Requires multiple queries
• Slower read performance compared to embedded model
• More complex data fetching