BAEL-6523: Difference Between findBy and findOneBy in Spring Data JPA (#14136)

persistence-modules/spring-data-jpa-repo-3/src/main/java/com/baeldung/spring/data/jpa/listrepositories/entity/Person.java

@@ -0,0 +1,38 @@
+package com.baeldung.spring.data.jpa.listrepositories.entity;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.Id;
+
+@Entity
+public class Person {
+
+    @Id
+    private int id;
+    private String firstName;
+    private String lastName;
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int 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;
+    }
+
+}

persistence-modules/spring-data-jpa-repo-3/src/main/java/com/baeldung/spring/data/jpa/listrepositories/repository/PersonRepository.java

@@ -0,0 +1,19 @@
+package com.baeldung.spring.data.jpa.listrepositories.repository;
+
+import java.util.List;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+import com.baeldung.spring.data.jpa.listrepositories.entity.Person;
+
+@Repository
+public interface PersonRepository extends JpaRepository<Person, Integer> {
+    Person findByFirstName(String firstName);
+
+    List<Person> findByLastName(String lastName);
+
+    Person findOneByFirstName(String firstName);
+
+    List<Person> findOneByLastName(String lastName);
+}

persistence-modules/spring-data-jpa-repo-3/src/main/resources/application.properties

@@ -1,2 +1,5 @@
+spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
+spring.jpa.hibernate.ddl-auto=none
+
 logging.level.org.hibernate.SQL=DEBUG
 logging.level.org.hibernate.type.descriptor.sql.BasicBinder=TRACE

persistence-modules/spring-data-jpa-repo-3/src/main/resources/data.sql

@@ -0,0 +1,4 @@
+INSERT INTO person (id, first_name, last_name) VALUES(1, 'Azhrioun', 'Abderrahim');
+INSERT INTO person (id, first_name, last_name) VALUES(2, 'Brian', 'Wheeler');
+INSERT INTO person (id, first_name, last_name) VALUES(3, 'Stella', 'Anderson');
+INSERT INTO person (id, first_name, last_name) VALUES(4, 'Stella', 'Wheeler');

persistence-modules/spring-data-jpa-repo-3/src/main/resources/schema.sql

@@ -0,0 +1,6 @@
+DROP TABLE IF EXISTS person;
+CREATE TABLE person(
+	id INT PRIMARY KEY,
+	first_name VARCHAR(200),
+	last_name VARCHAR(200)
+)

persistence-modules/spring-data-jpa-repo-3/src/test/java/com/baeldung/spring/data/jpa/listrepositories/repository/PersonRepositoryIntegrationTest.java

@@ -0,0 +1,66 @@
+package com.baeldung.spring.data.jpa.listrepositories.repository;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
+import org.springframework.dao.IncorrectResultSizeDataAccessException;
+
+import com.baeldung.spring.data.jpa.listrepositories.entity.Person;
+
+@DataJpaTest
+class PersonRepositoryIntegrationTest {
+
+    @Autowired
+    private PersonRepository personRepository;
+
+    @Test
+    void givenFirstName_whenCallingFindByFirstName_ThenReturnOnePerson() {
+        Person person = personRepository.findByFirstName("Azhrioun");
+
+        assertNotNull(person);
+        assertEquals("Abderrahim", person.getLastName());
+    }
+
+    @Test
+    void givenLastName_whenCallingFindByLastName_ThenReturnList() {
+        List<Person> person = personRepository.findByLastName("Wheeler");
+
+        assertEquals(2, person.size());
+    }
+
+    @Test
+    void givenFirstName_whenCallingFindOneByFirstName_ThenReturnOnePerson() {
+        Person person = personRepository.findOneByFirstName("Azhrioun");
+
+        assertNotNull(person);
+        assertEquals("Abderrahim", person.getLastName());
+    }
+
+    @Test
+    void givenLastName_whenCallingFindOneByLastName_ThenReturnList() {
+        List<Person> persons = personRepository.findOneByLastName("Wheeler");
+
+        assertEquals(2, persons.size());
+    }
+
+    @Test
+    void givenFirstName_whenCallingFindByFirstName_ThenThrowException() {
+        IncorrectResultSizeDataAccessException exception = assertThrows(IncorrectResultSizeDataAccessException.class, () -> personRepository.findByFirstName("Stella"));
+
+        assertEquals("query did not return a unique result: 2", exception.getMessage());
+    }
+
+    @Test
+    void givenFirstName_whenCallingFindOneByFirstName_ThenThrowException() {
+        IncorrectResultSizeDataAccessException exception = assertThrows(IncorrectResultSizeDataAccessException.class, () -> personRepository.findOneByFirstName("Stella"));
+
+        assertEquals("query did not return a unique result: 2", exception.getMessage());
+    }
+
+}