When updating a record of a junction object in Salesforce (an object used to create a many-to-many relationship), you must have the appropriate permissions.
Required Permissions:
Read/Write access on the junction object: To update the junction object record itself.
Read/Write access on both master (parent) records: Because the junction object is in two master-detail relationships, and its security settings are controlled by the parent records.
Given the options:
Option A: Read/Write access on the primary relationship
Option B: Read/Write access on the secondary relationship
These options correspond to having Read/Write access on both parent objects.
Supporting Reference:
Master-Detail Relationships:
Permissions Inheritance: The detail (junction) record inherits sharing and security settings from the master (parent) records.
Updating Records: To update a detail record, users must have Read/Write access to both the detail record and its parent records.
Reference:
Why Option C is Not Sufficient Alone:
Option C: Read/Write access on the junction object
Insufficient Alone: While necessary, having Read/Write access on the junction object alone is not enough.
Must Combine with Parent Access: Users also need Read/Write access on both master records due to the master-detail relationship.
Conclusion:
To update a junction object record, users must have Read/Write access on both the primary and secondary relationships (Options A and B).
This ensures proper permissions in the context of master-detail relationships.