Apex Developer Guide

Apex Developer Guide
Getting Started with Apex
Writing Apex
Data Types and Variables
Control Flow Statements
Classes, Objects, and Interfaces
Working with Data in Apex
Working with sObjects
Data Manipulation Language
SOQL and SOSL Queries
Working with SOQL and SOSL Query Results
Accessing sObject Fields Through Relationships
Understanding Foreign Key and Parent-Child Relationship SOQL Queries
Working with SOQL Aggregate Functions
Working with Very Large SOQL Queries
Using SOQL Queries That Return One Record
Improve Performance by Avoiding Null Values
Working with Polymorphic Relationships in SOQL Queries
Using Apex Variables in SOQL and SOSL Queries
Querying All Records with a SOQL Statement
SOQL For Loops
sObject Collections
Dynamic Apex
Apex Security and Sharing
Custom Settings
Running Apex
Debugging, Testing, and Deploying Apex
Apex Language Reference
Appendices
Glossary
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Accessing sObject Fields Through Relationships

sObject records represent relationships to other records with two fields: an ID and an address that points to a representation of the associated sObject. For example, the Contact sObject has both an AccountId field of type ID, and an Account field of type Account that points to the associated sObject record itself.

The ID field can be used to change the account with which the contact is associated, while the sObject reference field can be used to access data from the account. The reference field is only populated as the result of a SOQL or SOSL query (see note).

For example, the following Apex code shows how an account and a contact can be associated with one another, and then how the contact can be used to modify a field on the account:

To provide the most complete example, this code uses some elements that are described later in this guide:

Note

The expression c.Account.Name, and any other expression that traverses a relationship, displays slightly different characteristics when it is read as a value than when it is modified:

  • When being read as a value, if c.Account is null, then c.Account.Name evaluates to null, but does not yield a NullPointerException. This design allows developers to navigate multiple relationships without the tedium of having to check for null values.
  • When being modified, if c.Account is null, then c.Account.Name does yield a NullPointerException.

Note

In SOSL, you would access data for the inserted contact in a similar way to the SELECT statement used in the previous SOQL example.

In addition, the sObject field key can be used with insert, update, or upsert to resolve foreign keys by external ID. For example:

This inserts a new contact with the AccountId equal to the account with the external_id equal to ‘12345’. If there is no such account, the insert fails.

The following code is equivalent to the code above. However, because it uses a SOQL query, it is not as efficient. If this code was called multiple times, it could reach the execution limit for the maximum number of SOQL queries. For more information on execution limits, see Execution Governors and Limits.

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