When working with Salesforce, one of the most important concepts to understand is how objects relate to each other. Salesforce provides different types of relationships, and among them, the Master-Detail Relationship is one of the most powerful.

In this blog, we’ll break down everything you need to know about Master-Detail Relationships, explain how they work, where they should be used, and show diagrams for easy understanding.

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What is a Master-Detail Relationship?

A Master-Detail Relationship in Salesforce is a tight bond between two objects, where one object (the Detail) depends completely on the other object (the Master).

• The Master object controls the behavior of the Detail object.
  
• The Detail record cannot exist without its Master record.
  
• If the Master record is deleted, all related Detail records are also deleted (cascade delete).
  

👉 Think of it as a Parent-Child relationship.

• Parent = Master
  
• Child = Detail
  

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Key Features of Master-Detail Relationship

1. Ownership & Sharing
   
   • The Detail record does not have its own Owner field.
     
   • It inherits the sharing and security settings from the Master record.
     
2. Cascade Delete
   
   • If a Master record is deleted, all its associated Detail records are automatically deleted.
     
3. Roll-Up Summary Fields
   
   • Roll-up summary fields can be created on the Master object to perform calculations (SUM, COUNT, MIN, MAX) on fields from the Detail object.
     
4. Mandatory Relationship
   
   • While creating a Detail record, you must always link it to a Master record. It cannot exist independently.
     
5. Security & Access Control
   
   • The Detail record’s access is always controlled by the Master record’s access.
     

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Diagram for Easy Understanding

Here’s a simple diagram to visualize the relationship:

Example in Salesforce:

• Master: Account
  
• Detail: Contact (if we set it as Master-Detail)
  

If the Account is deleted, all its Contacts will also be deleted.

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Master-Detail vs. Lookup Relationship

It’s easy to confuse Master-Detail with Lookup Relationship, so let’s compare:

Feature	Master-Detail	Lookup
Dependency	Child must have a Parent	Child may exist without Parent
Ownership	Inherited from Master	Independent
Deletion Behavior	Cascade delete	No automatic delete
Roll-Up Summary	Supported	Not Supported
Security & Sharing	Controlled by Master	Independent

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Use Cases of Master-Detail Relationship

1. Invoices and Invoice Line Items
   
   • Invoice (Master)
     
   • Line Items (Detail)
     
2. If the invoice is deleted, all related line items should be deleted too.
   
3. Order and Order Products
   
   • Order (Master)
     
   • Products (Detail)
     
4. Products can’t exist without an Order.
   
5. Survey and Survey Responses
   
   • Survey (Master)
     
   • Responses (Detail)
     
6. Each response belongs to a survey and cannot exist on its own.
   

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How to Create a Master-Detail Relationship in Salesforce

1. Go to Setup → Object Manager.
   
2. Select the Detail object (the child).
   
3. Go to Fields & Relationships → New.
   
4. Choose Master-Detail Relationship.
   
5. Select the Master object (the parent).
   
6. Set up field-level security, layout, and save.
   

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Things to Keep in Mind

• A custom object can have up to 2 Master-Detail Relationships.
  
• Converting a Lookup to Master-Detail is possible (if all records have a parent).
  
• You cannot set a Master-Detail Relationship if the object already has existing records without a parent.
  

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Conclusion

The Master-Detail Relationship is a powerful way to enforce data dependency in Salesforce. It ensures that child records are always tied to a parent record, making data cleaner and more reliable. Features like cascade delete and roll-up summary fields make it one of the most widely used relationships in Salesforce.

👉 Remember:
Use Master-Detail when the child should not exist independently, and use Lookup when the child can stand alone.

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