Intermediate 25 min read

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 001XXXXXXXXXXXXXXX

Contact con = [SELECT Id, LastName, AccountId FROM Contact LIMIT 1]; — queries the relationship field directly.
System.debug(con.AccountId); — AccountId is the relationship field itself — 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 Industry

Contact con = [SELECT Id, LastName, Account.Name, Account.Industry FROM Contact LIMIT 1]; — querying Account.Name and Account.Industry alongside the Contact's own fields.
(blank line)
System.debug(con.Account.Name); — reaches straight through to the parent record's data with dot notation, without a second, separate query.
System.debug(con.Account.Industry); — same pattern for a second parent field.

(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 record

con.AccountId; — always exists once a Contact has a parent — just the Id.
con.Account; — the full related Account record, but only populated if the query explicitly asked for it.
con.Account.Name; — a specific field on that related record — trying to read this 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

Salesforce: ○ Not connected Connect

APEX

Execution Results

Run your code to see the result.

Relationships in Apex Quiz

1. What does con.AccountId hold?

Just the parent Account's Id, not its full field data The full Account record with all its fields Nothing, unless the Account was separately queried The Account's Name field

My Notes

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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.

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