Lookup Field creation is a few clicks. The decisions (parent object, cascade behavior, lookup filter) matter more than the click path.
- Open Fields & Relationships
Setup, Object Manager, the child object, Fields & Relationships, click New.
- Choose Lookup Relationship
Pick the Lookup Relationship field type. Master-Detail is for hard parent-child; Lookup is for the soft version.
- Pick the parent object
Choose which object the lookup points to. Multiple lookups to the same parent are supported.
- Set field label, name, and required flag
Enter the field label and API name. Decide whether the lookup is required.
- Configure parent-delete behavior
Pick Don''t Allow Deletion, Clear the Field, or Cascade Delete. Default is Clear.
- Add a lookup filter if needed
Configure lookup filter criteria to scope the dialog''s search results.
- Add to page layouts and FLS
Place the field on the relevant page layouts. Configure field-level security per profile.
Lookup Relationship.
The target of the lookup.
User-facing name and programmatic identifier.
Decides what happens to the child if the parent is deleted.
Narrows the dialog''s search scope.
- Lookup Fields are soft links. Children survive parent deletes by default (Clear behavior); the cascade behavior is configurable but defaults to soft.
- Polymorphic lookups (Task.WhatId, Event.WhatId) cannot be queried with dot notation across all parent types. Use TYPEOF for polymorphic queries.
- Lookup filters can be too restrictive. Test the filter against real user scenarios; over-filtering blocks legitimate workflows.
- Converting Lookup to Master-Detail is possible only when every child record has a populated parent. Required-from-day-one Lookup fields convert cleanly; optional ones often don''t.