Data Modeling and Management · Topic 1 of 3
Choosing a Data Model and Relationship Types
Salesforce data modeling: custom objects, lookup, master-detail, many-to-many junction, hierarchical and external relationships and their effects.
- 4 min
- Includes a diagram
- Use standard objects when they fit; create custom objects for the rest.
- Master-detail: detail has no owner, inherits sharing, cascade deletes, supports roll-ups.
- Lookup: independent records, optional link, no roll-up summary fields.
What it is
A data model is the set of objects, fields and relationships that store an app's data. Building a good one starts by checking whether a standard object already fits, such as Account, Contact or Case, before creating custom objects.
The relationship type you choose between objects affects ownership, sharing, deletion, roll-up summaries, page layouts and reporting. Many exam questions turn on that choice.
How it works
Relationship types
| Type | Key behaviour |
|---|---|
| Lookup | Loosely links two objects; the child keeps its own owner and sharing; the field can be optional |
| Master-detail | Tightly links a detail to its master; the detail has no owner, inherits sharing, and is deleted with its master |
| Many-to-many | Two master-detail relationships on a junction object |
| Hierarchical | A special lookup on the User object to another user, such as a manager |
| External lookup | Links an object to an external object using the external object's External ID |
| Indirect lookup | Links an external object to a Salesforce object using a unique External ID field on the Salesforce object |
Lookup versus master-detail
| Behaviour | Lookup | Master-detail |
|---|---|---|
| Child record owner | Its own owner | None; follows the master |
| Sharing | Its own | Controlled by parent |
| Field required | Optional or required | Always required |
| Deleting the parent | Clears the field or blocks deletion | Deletes the detail records too |
| Roll-up summary fields on parent | Not available | Available |
| Reparenting | Allowed | Only if "allow reparenting" is selected |
An object can be the detail in up to two master-detail relationships. Standard objects cannot be the detail side of a master-detail relationship.
Converting relationships
You can convert a lookup to master-detail only when every existing record has a value in the lookup field. Converting master-detail to lookup is possible only when no roll-up summary fields depend on the relationship.
Junction objects for many-to-many
When one record can relate to many records of another object, and the reverse is also true, create a junction object with two master-detail fields. For example, a Job Application object can link many candidates to many positions.
- The first master-detail field created is the primary relationship. The junction record's look and feel and its Owner value come from the primary master. To see a junction record, a user needs read access to both master records.
- Report types built from a junction object can include either master.
Effects on the user interface and reporting
- Master and lookup parents show the child in a related list on their page layout.
- Master-detail lets the master show roll-up summary fields, such as the count or total of its details.
- Standard report types are created for relationships, such as Positions with Job Applications.
A worked example: a training company tracks courses and students. A student can take many courses, and a course has many students. The builder creates an Enrollment__c junction object with master-detail fields to Course__c and Student__c, so each course can show a roll-up count of enrollments, and deleting a course removes its enrollments.
When the requirement mentions roll-up summaries, cascade delete or the child having no owner of its own, the answer is master-detail.
How the exam asks about this
- "Child records must keep their own owner and sharing." A lookup relationship.
- "The parent must show the total of its children's amounts." Master-detail with a roll-up summary.
- "Many records on each side." A junction object with two master-detail fields.
What to remember for the exam
- Use standard objects when they fit; create custom objects for the rest.
- Master-detail: detail has no owner, inherits sharing, cascade deletes, supports roll-ups.
- Lookup: independent records, optional link, no roll-up summary fields.
- Many-to-many needs a junction object with two master-detail fields; the first is primary.
- Hierarchical relationships exist only on the User object.
Deleting a master record deletes all of its detail records. If records must survive when the parent is deleted, use a lookup.
Common mistakes
Using a lookup when roll-up summaries are needed. Roll-up summary fields need master-detail.
Trying to make a standard object the detail. Standard objects cannot be on the detail side.
Converting to master-detail while some records have blank lookups. Fill every value first.
Check yourself
Which relationship lets the parent show a roll-up summary of its children?
A master-detail relationship.
How is a many-to-many relationship built in Salesforce?
With a junction object that has two master-detail relationship fields.
What must be true before converting a lookup to master-detail?
Every existing child record must have a value in the lookup field.
Topic 1 of 3 in Data Modeling and Management
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