Usage of the Hibernate @LazyCollection Annotation Article by Abdallah Sawan

persistence-modules/hibernate-annotations/src/main/java/com/baeldung/hibernate/model/Branch.java

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+package com.baeldung.hibernate.lazyCollection.model;
+
+import org.hibernate.annotations.LazyCollection;
+import org.hibernate.annotations.LazyCollectionOption;
+
+import javax.persistence.*;
+import java.util.ArrayList;
+import java.util.List;
+
+@Entity
+public class Branch {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String name;
+
+    public Branch() {
+    }
+    public Branch(String name) {
+        this.name = name;
+    }
+
+    @OneToMany(mappedBy = "mainBranch")
+    @LazyCollection(LazyCollectionOption.TRUE)
+    private List<Employee> mainEmployees;
+
+    @OneToMany(mappedBy = "subBranch")
+    @LazyCollection(LazyCollectionOption.FALSE)
+    private List<Employee> subEmployees;
+
+    @OneToMany(mappedBy = "additionalBranch")
+    @LazyCollection(LazyCollectionOption.EXTRA)
+    @OrderColumn(name = "id")
+    private List<Employee> additionalEmployees;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public List<Employee> getMainEmployees() {
+        return mainEmployees;
+    }
+
+    public void setMainEmployees(List<Employee> mainEmployees) {
+        this.mainEmployees = mainEmployees;
+    }
+
+    public List<Employee> getSubEmployees() {
+        return subEmployees;
+    }
+
+    public void setSubEmployees(List<Employee> subEmployees) {
+        this.subEmployees = subEmployees;
+    }
+
+    public List<Employee> getAdditionalEmployees() {
+        return additionalEmployees;
+    }
+
+    public void setAdditionalEmployees(List<Employee> additionalEmployees) {
+        this.additionalEmployees = additionalEmployees;
+    }
+
+    public void addMainEmployee(Employee employee) {
+        if (this.mainEmployees == null) {
+            this.mainEmployees = new ArrayList<>();
+        }
+        this.mainEmployees.add(employee);
+    }
+
+    public void addSubEmployee(Employee employee) {
+        if (this.subEmployees == null) {
+            this.subEmployees = new ArrayList<>();
+        }
+        this.subEmployees.add(employee);
+    }
+
+    public void addAdditionalEmployee(Employee employee) {
+        if (this.additionalEmployees == null) {
+            this.additionalEmployees = new ArrayList<>();
+        }
+        this.additionalEmployees.add(employee);
+    }
+}

persistence-modules/hibernate-annotations/src/main/java/com/baeldung/hibernate/model/Employee.java

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+package com.baeldung.hibernate.lazyCollection.model;
+
+import javax.persistence.*;
+
+@Entity
+public class Employee {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    private String name;
+
+    private Long rank;
+
+    public Employee() {
+
+    }
+
+    public Employee(String name, Long rank, Branch mainBranch, Branch subBranch, Branch additionalBranch) {
+        this.name = name;
+        this.rank = rank;
+        this.mainBranch = mainBranch;
+        this.subBranch = subBranch;
+        this.additionalBranch = additionalBranch;
+    }
+
+    @ManyToOne
+    private Branch mainBranch;
+
+    @ManyToOne
+    private Branch subBranch;
+
+    @ManyToOne
+    private Branch additionalBranch;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public Long getRank() {
+        return rank;
+    }
+
+    public void setRank(Long rank) {
+        this.rank = rank;
+    }
+
+    public Branch getMainBranch() {
+        return mainBranch;
+    }
+
+    public void setMainBranch(Branch mainBranch) {
+        this.mainBranch = mainBranch;
+    }
+
+    public Branch getSubBranch() {
+        return subBranch;
+    }
+
+    public void setSubBranch(Branch subBranch) {
+        this.subBranch = subBranch;
+    }
+
+    public Branch getAdditionalBranch() {
+        return additionalBranch;
+    }
+
+    public void setAdditionalBranch(Branch additionalBranch) {
+        this.additionalBranch = additionalBranch;
+    }
+}

persistence-modules/hibernate-annotations/src/test/java/com/baeldung/hibernate/lazyCollection/LazyCollectionTests.java

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+package com.baeldung.hibernate.lazyCollection;
+
+import com.baeldung.hibernate.lazyCollection.model.Branch;
+import com.baeldung.hibernate.lazyCollection.model.Employee;
+import org.hibernate.Hibernate;
+import org.hibernate.Session;
+import org.hibernate.SessionFactory;
+import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
+import org.hibernate.cfg.Configuration;
+import org.hibernate.dialect.H2Dialect;
+import org.hibernate.service.ServiceRegistry;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+
+import javax.annotation.PostConstruct;
+
+@SpringBootTest
+public class LazyCollectionTests {
+
+    private static SessionFactory sessionFactory;
+
+    private Session session;
+
+    Branch branch;
+
+    @PostConstruct
+    public void beforeTests() {
+        Configuration configuration = new Configuration().addAnnotatedClass(Branch.class).addAnnotatedClass(Employee.class)
+                .setProperty("hibernate.dialect", H2Dialect.class.getName())
+                .setProperty("hibernate.connection.driver_class", org.h2.Driver.class.getName())
+                .setProperty("hibernate.connection.url", "jdbc:h2:mem:test")
+                .setProperty("hibernate.connection.username", "sa").setProperty("hibernate.connection.password", "")
+                .setProperty("hibernate.hbm2ddl.auto", "update");
+        ServiceRegistry serviceRegistry = new StandardServiceRegistryBuilder()
+                .applySettings(configuration.getProperties()).build();
+
+        sessionFactory = configuration.buildSessionFactory(serviceRegistry);
+
+        setUp();
+    }
+
+    private void setUp() {
+        session = sessionFactory.openSession();
+        session.beginTransaction();
+
+        branch = new Branch("Main Branch");
+
+        session.save(branch);
+
+        Employee mainEmployee1 = new Employee("main employee 1",1L,  branch, null, null);
+        Employee mainEmployee2 = new Employee("main employee 2", 2L, branch, null, null);
+        Employee mainEmployee3 = new Employee("main employee 3", 3L, branch, null, null);
+
+        session.save(mainEmployee1);
+        session.save(mainEmployee2);
+        session.save(mainEmployee3);
+
+        Employee subEmployee1 = new Employee("sub employee 1", 1L, null, branch, null);
+        Employee subEmployee2 = new Employee("sub employee 2", 2L, null, branch, null);
+        Employee subEmployee3 = new Employee("sub employee 3", 3L, null, branch, null);
+
+        session.save(subEmployee1);
+        session.save(subEmployee2);
+        session.save(subEmployee3);
+
+        Employee additionalEmployee1 = new Employee("additional employee 1", 1L, null, null, branch);
+        Employee additionalEmployee2 = new Employee("additional employee 2", 2L, null, null, branch);
+        Employee additionalEmployee3 = new Employee("additional employee 3", 3L, null, null, branch);
+
+        session.save(additionalEmployee1);
+        session.save(additionalEmployee2);
+        session.save(additionalEmployee3);
+
+        session.flush();
+        session.refresh(branch);
+        session.getTransaction().commit();
+        session.close();
+    }
+
+    @Test
+    public void testLazyFetching() {
+        Assertions.assertFalse(Hibernate.isInitialized(branch.getMainEmployees()));
+    }
+
+    @Test
+    public void testEagerFetching() {
+        Assertions.assertTrue(Hibernate.isInitialized(branch.getSubEmployees()));
+    }
+
+    @Test
+    public void testExtraFetching() {
+        Assertions.assertFalse(Hibernate.isInitialized(branch.getAdditionalEmployees()));
+    }
+}