Relationships in Apex
By the end of this lesson, you'll be able to:
- Access a parent record's field through a lookup or master-detail relationship
- Explain the dot-notation path used to traverse a relationship
- Recognize the difference between a relationship field (the Id) and the related record itself
Prerequisites: "Custom Fields"
A relationship field holds an Id
Contact con = [SELECT Id, LastName, AccountId FROM Contact LIMIT 1];
System.debug(con.AccountId); // an 18-character Id, like 001XXXXXXXXXXXXXXXAccountId on Contact is the relationship field itself — it's just an Id value pointing at a specific Account record, not the Account record's actual data.
Traversing to the parent's fields
Contact con = [SELECT Id, LastName, Account.Name, Account.Industry FROM Contact LIMIT 1];
System.debug(con.Account.Name); // the parent Account's Name
System.debug(con.Account.Industry); // the parent Account's IndustryQuerying Account.Name and Account.Industry alongside the Contact's own fields lets you reach straight through to the parent record's data with dot notation — con.Account.Name — without a second, separate query. (SOQL relationship queries get a full module of their own shortly.)
The relationship field vs the related record
con.AccountId; // the parent's Id only — a simple relationship field
con.Account; // the full related Account record (if queried)
con.Account.Name; // a specific field on that related recordAccountId and Account are related but distinct: AccountId always exists once a Contact has a parent, but con.Account (and anything under it) is only populated if the query explicitly asked for it — trying to read con.Account.Name without having queried Account.Name throws a runtime error.
Exercise
Write a SOQL query on Contact that selects Id, LastName, and the parent Account's Name and Industry, then debug the parent Account's Name for the first result.
Show hint
SELECT Id, LastName, Account.Name, Account.Industry FROM Contact LIMIT 1
Relationships in Apex Quiz
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Summary
A relationship connects one record to another — Apex lets you traverse from a child record straight to its parent's fields using dot notation, once the parent has been queried alongside it.