Standard & Custom Objects, Relationships

1// Working with objects and relationships in Apex
2
3// Creating records with relationships
4public class DataModelExamples {
5    
6    // 1. Creating parent-child records (Account → Contact)
7    public static void createAccountWithContacts() {
8        // Create parent
9        Account corp = new Account(
10            Name = 'Acme Corporation',
11            Industry = 'Technology',
12            BillingCity = 'San Francisco'
13        );
14        insert corp;
15        
16        // Create children with relationship
17        List<Contact> contacts = new List<Contact>{
18            new Contact(
19                FirstName = 'John', 
20                LastName = 'Doe',
21                AccountId = corp.Id,  // Lookup relationship
22                Email = 'john@acme.com'
23            ),
24            new Contact(
25                FirstName = 'Jane', 
26                LastName = 'Smith',
27                AccountId = corp.Id,
28                Email = 'jane@acme.com'
29            )
30        };
31        insert contacts;
32    }
33    
34    // 2. Querying across relationships
35    public static void queryRelationships() {
36        // Parent-to-child (subquery) — "Get account and its contacts"
37        List<Account> accounts = [
38            SELECT Name, Industry,
39                (SELECT FirstName, LastName, Email 
40                 FROM Contacts  // Child relationship name
41                 WHERE Email != null
42                 ORDER BY LastName)
43            FROM Account
44            WHERE Industry = 'Technology'
45            LIMIT 10
46        ];
47        
48        // Child-to-parent (dot notation) — "Get contact and its account info"
49        List<Contact> contacts = [
50            SELECT FirstName, LastName,
51                Account.Name,           // Parent field
52                Account.Industry,       // Navigate up the relationship
53                Account.Owner.Name      // Navigate multiple levels
54            FROM Contact
55            WHERE Account.Industry = 'Technology'
56        ];
57        
58        // Working with results
59        for (Account acc : accounts) {
60            System.debug('Account: ' + acc.Name);
61            for (Contact c : acc.Contacts) {  // Access child records
62                System.debug('  Contact: ' + c.FirstName + ' ' + c.LastName);
63            }
64        }
65    }
66    
67    // 3. Junction Object pattern (Many-to-Many)
68    // Student__c <---> Course_Enrollment__c <---> Course__c
69    public static void createManyToMany() {
70        // Assume Student__c and Course__c already exist
71        // Create junction records
72        List<Course_Enrollment__c> enrollments = new List<Course_Enrollment__c>();
73        
74        // Enroll student in multiple courses
75        for (Id courseId : courseIds) {
76            enrollments.add(new Course_Enrollment__c(
77                Student__c = studentId,         // Master-Detail 1
78                Course__c = courseId,            // Master-Detail 2
79                Enrollment_Date__c = Date.today(),
80                Status__c = 'Active'
81            ));
82        }
83        insert enrollments;
84    }
85    
86    // 4. Dynamic relationship queries
87    public static List<SObject> getRelatedRecords(
88        Id parentId, String childObject, String relationshipField
89    ) {
90        String query = 'SELECT Id, Name FROM ' + 
91            String.escapeSingleQuotes(childObject) + 
92            ' WHERE ' + String.escapeSingleQuotes(relationshipField) + 
93            ' = :parentId';
94        return Database.query(query);
95    }
96    
97    // 5. Schema Describe — inspect relationships at runtime
98    public static void describeRelationships(String objectName) {
99        Schema.DescribeSObjectResult objDescribe = 
100            Schema.getGlobalDescribe().get(objectName).getDescribe();
101        
102        // Get all child relationships
103        List<Schema.ChildRelationship> children = objDescribe.getChildRelationships();
104        for (Schema.ChildRelationship child : children) {
105            System.debug('Child Object: ' + child.getChildSObject());
106            System.debug('Relationship Name: ' + child.getRelationshipName());
107            System.debug('Field: ' + child.getField());
108        }
109    }
110}