BAEL-2811: Added sample code for jpa joins (#6691)

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/joins/model/Department.java

@@ -0,0 +1,45 @@
+package com.baeldung.joins.model;
+
+import java.util.List;
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.OneToMany;
+
+@Entity
+public class Department {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private long id;
+
+    private String name;
+
+    @OneToMany(mappedBy = "department")
+    private List<Employee> employees;
+
+    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> getEmployees() {
+        return employees;
+    }
+
+    public void setEmployees(List<Employee> employees) {
+        this.employees = employees;
+    }
+}

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/joins/model/Employee.java

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+package com.baeldung.joins.model;
+
+import java.util.List;
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.ManyToOne;
+import javax.persistence.OneToMany;
+import javax.persistence.Table;
+
+@Entity
+@Table(name = "joins_employee")
+public class Employee {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private long id;
+
+    private String name;
+
+    private int age;
+
+    @ManyToOne
+    private Department department;
+
+    @OneToMany(mappedBy = "employee")
+    private List<Phone> phones;
+
+    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 int getAge() {
+        return age;
+    }
+
+    public void setAge(int age) {
+        this.age = age;
+    }
+
+    public Department getDepartment() {
+        return department;
+    }
+
+    public void setDepartment(Department department) {
+        this.department = department;
+    }
+
+    public List<Phone> getPhones() {
+        return phones;
+    }
+
+    public void setPhones(List<Phone> phones) {
+        this.phones = phones;
+    }
+}

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/joins/model/Phone.java

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+package com.baeldung.joins.model;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.ManyToOne;
+
+@Entity
+public class Phone {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private long id;
+
+    private String number;
+
+    @ManyToOne
+    private Employee employee;
+
+    public long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+
+    public String getNumber() {
+        return number;
+    }
+
+    public void setNumber(String number) {
+        this.number = number;
+    }
+
+    public Employee getEmployee() {
+        return employee;
+    }
+
+    public void setEmployee(Employee employee) {
+        this.employee = employee;
+    }
+}

persistence-modules/spring-data-jpa-2/src/main/resources/application-joins.properties

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+spring.datasource.data=classpath:db/import_joins.sql

persistence-modules/spring-data-jpa-2/src/main/resources/db/import_joins.sql

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+INSERT INTO department (id, name) VALUES (1, 'Infra');
+INSERT INTO department (id, name) VALUES (2, 'Accounting');
+INSERT INTO department (id, name) VALUES (3, 'Management');
+
+INSERT INTO joins_employee (id, name, age, department_id) VALUES (1, 'Baeldung', '35', 1);
+INSERT INTO joins_employee (id, name, age, department_id) VALUES (2, 'John', '35', 2);
+INSERT INTO joins_employee (id, name, age, department_id) VALUES (3, 'Jane', '35', 2);
+
+INSERT INTO phone (id, number, employee_id) VALUES (1, '111', 1);
+INSERT INTO phone (id, number, employee_id) VALUES (2, '222', 1);
+INSERT INTO phone (id, number, employee_id) VALUES (3, '333', 1);
+
+COMMIT;

persistence-modules/spring-data-jpa-2/src/test/java/com/baeldung/joins/JpaJoinsIntegrationTest.java

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+package com.baeldung.joins;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.baeldung.joins.model.Department;
+import com.baeldung.joins.model.Phone;
+import java.util.List;
+import javax.persistence.EntityManager;
+import javax.persistence.PersistenceContext;
+import javax.persistence.TypedQuery;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.junit4.SpringRunner;
+
+@RunWith(SpringRunner.class)
+@DataJpaTest
+@ActiveProfiles("joins")
+public class JpaJoinsIntegrationTest {
+
+    @PersistenceContext
+    private EntityManager entityManager;
+
+    @Test
+    public void whenPathExpressionIsUsedForSingleValuedAssociation_thenCreatesImplicitInnerJoin() {
+        TypedQuery<Department> query = entityManager.createQuery("SELECT e.department FROM Employee e", Department.class);
+
+        List<Department> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(3);
+        assertThat(resultList).extracting("name")
+            .containsOnly("Infra", "Accounting", "Accounting");
+    }
+
+    @Test
+    public void whenJoinKeywordIsUsed_thenCreatesExplicitInnerJoin() {
+        TypedQuery<Department> query = entityManager.createQuery("SELECT d FROM Employee e JOIN e.department d", Department.class);
+
+        List<Department> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(3);
+        assertThat(resultList).extracting("name")
+            .containsOnly("Infra", "Accounting", "Accounting");
+    }
+
+    @Test
+    public void whenInnerJoinKeywordIsUsed_thenCreatesExplicitInnerJoin() {
+        TypedQuery<Department> query = entityManager.createQuery("SELECT d FROM Employee e INNER JOIN e.department d", Department.class);
+
+        List<Department> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(3);
+        assertThat(resultList).extracting("name")
+            .containsOnly("Infra", "Accounting", "Accounting");
+    }
+
+    @Test
+    public void whenEntitiesAreListedInFromAndMatchedInWhere_ThenCreatesJoin() {
+        TypedQuery<Department> query = entityManager.createQuery("SELECT d FROM Employee e, Department d WHERE e.department = d", Department.class);
+
+        List<Department> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(3);
+        assertThat(resultList).extracting("name")
+            .containsOnly("Infra", "Accounting", "Accounting");
+    }
+
+    @Test
+    public void whenEntitiesAreListedInFrom_ThenCreatesCartesianProduct() {
+        TypedQuery<Department> query = entityManager.createQuery("SELECT d FROM Employee e, Department d", Department.class);
+
+        List<Department> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(9);
+        assertThat(resultList).extracting("name")
+            .containsOnly("Infra", "Accounting", "Management", "Infra", "Accounting", "Management", "Infra", "Accounting", "Management");
+    }
+
+    @Test
+    public void whenCollectionValuedAssociationIsJoined_ThenCanSelect() {
+        TypedQuery<Phone> query = entityManager.createQuery("SELECT ph FROM Employee e JOIN e.phones ph ", Phone.class);
+
+        List<Phone> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(3);
+    }
+
+    @Test
+    public void whenMultipleEntitiesAreListedWithJoin_ThenCreatesMultipleJoins() {
+        TypedQuery<Phone> query = entityManager.createQuery("SELECT ph FROM Employee e JOIN e.department d JOIN e.phones ph WHERE d.name IS NOT NULL", Phone.class);
+
+        List<Phone> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(3);
+        assertThat(resultList).extracting("number")
+            .containsOnly("111", "222", "333");
+    }
+
+    @Test
+    public void whenLeftKeywordIsSpecified_thenCreatesOuterJoinAndIncludesNonMatched() {
+        TypedQuery<Department> query = entityManager.createQuery("SELECT DISTINCT d FROM Department d LEFT JOIN d.employees e", Department.class);
+
+        List<Department> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(3);
+        assertThat(resultList).extracting("name")
+            .containsOnly("Infra", "Accounting", "Management");
+    }
+
+    @Test
+    public void whenFetchKeywordIsSpecified_ThenCreatesFetchJoin() {
+        TypedQuery<Department> query = entityManager.createQuery("SELECT d FROM Department d JOIN FETCH d.employees", Department.class);
+
+        List<Department> resultList = query.getResultList();
+
+        assertThat(resultList).hasSize(3);
+        assertThat(resultList).extracting("name")
+            .containsOnly("Infra", "Accounting", "Accounting");
+    }
+
+    @Test
+    public void whenLeftAndFetchKeywordsAreSpecified_ThenCreatesOuterFetchJoin() {
+        TypedQuery<Department> query = entityManager.createQuery("SELECT d FROM Department d LEFT JOIN FETCH d.employees", Department.class);
+        List<Department> resultList = query.getResultList();
+        assertThat(resultList).hasSize(4);
+        assertThat(resultList).extracting("name")
+            .containsOnly("Infra", "Accounting", "Accounting", "Management");
+    }
+}