Spring Data JPA projections (#6733)

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/projection/model/Address.java

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+package com.baeldung.projection.model;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+import javax.persistence.OneToOne;
+
+@Entity
+public class Address {
+    @Id
+    private Long id;
+    @OneToOne
+    private Person person;
+    private String state;
+    private String city;
+    private String street;
+    private String zipCode;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getState() {
+        return state;
+    }
+
+    public void setState(String state) {
+        this.state = state;
+    }
+
+    public String getCity() {
+        return city;
+    }
+
+    public void setCity(String city) {
+        this.city = city;
+    }
+
+    public String getStreet() {
+        return street;
+    }
+
+    public void setStreet(String street) {
+        this.street = street;
+    }
+
+    public String getZipCode() {
+        return zipCode;
+    }
+
+    public void setZipCode(String zipCode) {
+        this.zipCode = zipCode;
+    }
+}

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/projection/model/Person.java

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+package com.baeldung.projection.model;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+import javax.persistence.OneToOne;
+
+@Entity
+public class Person {
+    @Id
+    private Long id;
+    private String firstName;
+    private String lastName;
+    @OneToOne(mappedBy = "person")
+    private Address address;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public Address getAddress() {
+        return address;
+    }
+
+    public void setAddress(Address address) {
+        this.address = address;
+    }
+}

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/projection/repository/AddressRepository.java

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+package com.baeldung.projection.repository;
+
+import com.baeldung.projection.view.AddressView;
+import com.baeldung.projection.model.Address;
+import org.springframework.data.repository.Repository;
+
+import java.util.List;
+
+public interface AddressRepository extends Repository<Address, Long> {
+    List<AddressView> getAddressByState(String state);
+}

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/projection/repository/PersonRepository.java

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+package com.baeldung.projection.repository;
+
+import com.baeldung.projection.model.Person;
+import com.baeldung.projection.view.PersonDto;
+import com.baeldung.projection.view.PersonView;
+import org.springframework.data.repository.Repository;
+
+public interface PersonRepository extends Repository<Person, Long> {
+    PersonView findByLastName(String lastName);
+
+    PersonDto findByFirstName(String firstName);
+
+    <T> T findByLastName(String lastName, Class<T> type);
+}

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/projection/view/AddressView.java

@@ -0,0 +1,7 @@
+package com.baeldung.projection.view;
+
+public interface AddressView {
+    String getZipCode();
+
+    PersonView getPerson();
+}

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/projection/view/PersonDto.java

@@ -0,0 +1,34 @@
+package com.baeldung.projection.view;
+
+import java.util.Objects;
+
+public class PersonDto {
+    private final String firstName;
+    private final String lastName;
+
+    public PersonDto(String firstName, String lastName) {
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        PersonDto personDto = (PersonDto) o;
+        return Objects.equals(firstName, personDto.firstName) && Objects.equals(lastName, personDto.lastName);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(firstName, lastName);
+    }
+}

persistence-modules/spring-data-jpa-2/src/main/java/com/baeldung/projection/view/PersonView.java

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+package com.baeldung.projection.view;
+
+import org.springframework.beans.factory.annotation.Value;
+
+public interface PersonView {
+    String getFirstName();
+
+    String getLastName();
+
+    @Value("#{target.firstName + ' ' + target.lastName}")
+    String getFullName();
+}

persistence-modules/spring-data-jpa-2/src/test/java/com/baeldung/projection/JpaProjectionIntegrationTest.java

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+package com.baeldung.projection;
+
+import com.baeldung.projection.model.Person;
+import com.baeldung.projection.repository.AddressRepository;
+import com.baeldung.projection.repository.PersonRepository;
+import com.baeldung.projection.view.AddressView;
+import com.baeldung.projection.view.PersonDto;
+import com.baeldung.projection.view.PersonView;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
+import org.springframework.test.context.jdbc.Sql;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.context.jdbc.Sql.ExecutionPhase.AFTER_TEST_METHOD;
+
+@DataJpaTest
+@RunWith(SpringRunner.class)
+@Sql(scripts = "/projection-insert-data.sql")
+@Sql(scripts = "/projection-clean-up-data.sql", executionPhase = AFTER_TEST_METHOD)
+public class JpaProjectionIntegrationTest {
+    @Autowired
+    private AddressRepository addressRepository;
+
+    @Autowired
+    private PersonRepository personRepository;
+
+    @Test
+    public void whenUsingClosedProjections_thenViewWithRequiredPropertiesIsReturned() {
+        AddressView addressView = addressRepository.getAddressByState("CA").get(0);
+        assertThat(addressView.getZipCode()).isEqualTo("90001");
+
+        PersonView personView = addressView.getPerson();
+        assertThat(personView.getFirstName()).isEqualTo("John");
+        assertThat(personView.getLastName()).isEqualTo("Doe");
+    }
+
+    @Test
+    public void whenUsingOpenProjections_thenViewWithRequiredPropertiesIsReturned() {
+        PersonView personView = personRepository.findByLastName("Doe");
+        assertThat(personView.getFullName()).isEqualTo("John Doe");
+    }
+
+    @Test
+    public void whenUsingClassBasedProjections_thenDtoWithRequiredPropertiesIsReturned() {
+        PersonDto personDto = personRepository.findByFirstName("John");
+        assertThat(personDto.getFirstName()).isEqualTo("John");
+        assertThat(personDto.getLastName()).isEqualTo("Doe");
+    }
+
+    @Test
+    public void whenUsingDynamicProjections_thenObjectWithRequiredPropertiesIsReturned() {
+        Person person = personRepository.findByLastName("Doe", Person.class);
+        PersonView personView = personRepository.findByLastName("Doe", PersonView.class);
+        PersonDto personDto = personRepository.findByLastName("Doe", PersonDto.class);
+
+        assertThat(person.getFirstName()).isEqualTo("John");
+        assertThat(personView.getFirstName()).isEqualTo("John");
+        assertThat(personDto.getFirstName()).isEqualTo("John");
+    }
+}

persistence-modules/spring-data-jpa-2/src/test/resources/projection-clean-up-data.sql

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+DELETE FROM address;
+DELETE FROM person;

persistence-modules/spring-data-jpa-2/src/test/resources/projection-insert-data.sql

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+INSERT INTO person(id,first_name,last_name) VALUES (1,'John','Doe');
+INSERT INTO address(id,person_id,state,city,street,zip_code) VALUES (1,1,'CA', 'Los Angeles', 'Standford Ave', '90001');