✨ init basic logic of follow

backend/src/main/java/net/pengcook/follow/entity/Follow.java

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+package net.pengcook.follow.entity;
+
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.Table;
+import jakarta.persistence.UniqueConstraint;
+import lombok.AccessLevel;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import net.pengcook.user.domain.User;
+
+@Entity
+@Getter
+@Table(uniqueConstraints = {@UniqueConstraint(columnNames = {"follower_id", "followee_id"})})
+@NoArgsConstructor(access = AccessLevel.PROTECTED)
+@AllArgsConstructor(access = AccessLevel.PRIVATE)
+public class Follow {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private long id;
+
+    @ManyToOne
+    @JoinColumn(name = "follower_id")
+    private User follower;
+
+    @ManyToOne
+    @JoinColumn(name = "followee_id")
+    private User followee;
+
+    public Follow(User follower, User followee) {
+        this(0L, follower, followee);
+    }
+}

backend/src/main/java/net/pengcook/follow/exception/UserNotFoundException.java

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+package net.pengcook.follow.exception;
+
+import net.pengcook.exception.DomainException;
+import org.springframework.http.HttpStatus;
+
+public class UserNotFoundException extends DomainException {
+
+    public UserNotFoundException(String message) {
+        super(HttpStatus.NOT_FOUND, message);
+    }
+}

backend/src/main/java/net/pengcook/follow/repository/FollowRepository.java

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+package net.pengcook.follow.repository;
+
+import net.pengcook.follow.entity.Follow;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface FollowRepository extends JpaRepository<Follow, Long> {
+
+    void deleteByFollowerIdAndFolloweeId(long followerId, long followeeId);
+}

backend/src/main/java/net/pengcook/follow/service/FollowService.java

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+package net.pengcook.follow.service;
+
+import lombok.RequiredArgsConstructor;
+import net.pengcook.authentication.domain.UserInfo;
+import net.pengcook.follow.entity.Follow;
+import net.pengcook.follow.exception.UserNotFoundException;
+import net.pengcook.follow.repository.FollowRepository;
+import net.pengcook.user.domain.User;
+import net.pengcook.user.repository.UserRepository;
+import org.springframework.stereotype.Service;
+
+@Service
+@RequiredArgsConstructor
+public class FollowService {
+
+    private final FollowRepository followRepository;
+    private final UserRepository userRepository;
+
+    public void follow(UserInfo userInfo, long followeeId) {
+        User follower = userRepository.findById(userInfo.getId())
+                .orElseThrow(() -> new UserNotFoundException("팔로워가 존재하지 않습니다."));
+        User followee = userRepository.findById(followeeId)
+                .orElseThrow(() -> new UserNotFoundException("팔로이가 존재하지 않습니다."));
+
+        followRepository.save(new Follow(follower, followee));
+    }
+
+    public void unfollow(UserInfo userInfo, long followeeId) {
+        followRepository.deleteByFollowerIdAndFolloweeId(userInfo.getId(), followeeId);
+    }
+}

backend/src/test/java/net/pengcook/follow/service/FollowServiceTest.java

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+package net.pengcook.follow.service;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
+
+@DataJpaTest
+class FollowServiceTest {
+
+    @Test
+    @DisplayName("한 사람이 다른 사람을 팔로우 한다.")
+    void follow() {
+
+    }
+}

backend/src/test/resources/data/follow.sql

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+SET
+REFERENTIAL_INTEGRITY FALSE;
+
+TRUNCATE TABLE users;
+ALTER TABLE users
+    ALTER COLUMN id RESTART;
+
+TRUNCATE TABLE follow;
+ALTER TABLE follow
+    ALTER COLUMN id RESTART;
+
+SET
+REFERENTIAL_INTEGRITY TRUE;
+
+INSERT INTO users (email, username, nickname, image, region)
+VALUES ('[email protected]', 'ela', '엘라', 'ela.jpg', 'KOREA'),
+       ('[email protected]', 'loki', '로키', 'loki.jpg', 'KOREA'),
+       ('[email protected]', 'seyang', '새양', 'seyang.jpg', 'GERMANY');