BAEL-6119: Difference Between findBy and findAllBy in Spring Data JPA (#13344)

* player entity and repository. test structure

* moving modules

* test findFirst. cleanups.

* adding @Repository

* player entity and repository. test structure

* moving modules

* test findFirst. cleanups.

* adding @Repository

* changing module

* adding show-sql config

* removing unrelated change

* properties SB annotation

persistence-modules/spring-data-jpa-repo-2/src/main/java/com/baeldung/spring/data/persistence/findbyvsfindallby/FindByVsFindAllByApplication.java

@@ -0,0 +1,11 @@
+package com.baeldung.spring.data.persistence.findbyvsfindallby;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class FindByVsFindAllByApplication {
+    public static void main(String[] args) {
+        SpringApplication.run(FindByVsFindAllByApplication.class, args);
+    }
+}

persistence-modules/spring-data-jpa-repo-2/src/main/java/com/baeldung/spring/data/persistence/findbyvsfindallby/model/Player.java

@@ -0,0 +1,43 @@
+package com.baeldung.spring.data.persistence.findbyvsfindallby.model;
+
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import java.util.Objects;
+
+@Entity
+public class Player {
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private long id;
+
+    private Integer score;
+
+    public Player(Integer score) {
+        this.score = score;
+    }
+
+    public Player() {
+    }
+
+    public long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+
+    public Integer getScore() {
+        return score;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Player player = (Player) o;
+        return id == player.id && Objects.equals(score, player.score);
+    }
+}

persistence-modules/spring-data-jpa-repo-2/src/main/java/com/baeldung/spring/data/persistence/findbyvsfindallby/repository/PlayerRepository.java

@@ -0,0 +1,17 @@
+package com.baeldung.spring.data.persistence.findbyvsfindallby.repository;
+
+import com.baeldung.spring.data.persistence.findbyvsfindallby.model.Player;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+import java.util.List;
+import java.util.Optional;
+
+@Repository
+public interface PlayerRepository extends JpaRepository<Player, Long> {
+    List<Player> findByScoreGreaterThan(Integer target);
+
+    List<Player> findAllByScoreGreaterThan(Integer target);
+
+    Optional<Player> findFirstByScoreGreaterThan(Integer target);
+}

persistence-modules/spring-data-jpa-repo-2/src/test/java/com/baeldung/spring/data/persistence/findbyvsfindallby/FindByVsFindAllByIntegrationTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.spring.data.persistence.findbyvsfindallby;
+
+import com.baeldung.spring.data.persistence.findbyvsfindallby.model.Player;
+import com.baeldung.spring.data.persistence.findbyvsfindallby.repository.PlayerRepository;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Optional;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+@RunWith(SpringRunner.class)
+@SpringBootTest(classes = FindByVsFindAllByApplication.class, properties = "spring.jpa.show-sql=true")
+public class FindByVsFindAllByIntegrationTest {
+    @Autowired
+    private PlayerRepository playerRepository;
+
+    @Before
+    public void setup() {
+        Player player1 = new Player(600);
+        Player player2 = new Player(500);
+        Player player3 = new Player(300);
+        playerRepository.saveAll(Arrays.asList(player1, player2, player3));
+    }
+
+    @Test
+    public void givenSavedPlayer_whenUseFindByOrFindAllBy_thenReturnSameResult() {
+        List<Player> findByPlayers = playerRepository.findByScoreGreaterThan(400);
+        List<Player> findAllByPlayers = playerRepository.findAllByScoreGreaterThan(400);
+        assertEquals(findByPlayers, findAllByPlayers);
+    }
+
+    @Test
+    public void givenSavedPlayer_whenUseFindFirst_thenReturnSingleResult() {
+        Optional<Player> player = playerRepository.findFirstByScoreGreaterThan(400);
+        assertTrue(player.isPresent());
+        assertEquals(600, player.get().getScore());
+    }
+}