feat(recommend): 추천 크리에이터 동시 팔로우 서비스를 추가한다

src/main/kotlin/kr/co/vividnext/sodalive/member/following/CreatorFollowing.kt

@@ -6,9 +6,19 @@ import javax.persistence.Entity
 import javax.persistence.FetchType
 import javax.persistence.JoinColumn
 import javax.persistence.ManyToOne
+import javax.persistence.Table
+import javax.persistence.UniqueConstraint
 
 @Entity
-data class CreatorFollowing(
+@Table(
+    uniqueConstraints = [
+        UniqueConstraint(
+            name = "uk_creator_following_member_creator",
+            columnNames = ["member_id", "creator_id"]
+        )
+    ]
+)
+class CreatorFollowing(
     var isNotify: Boolean = true,
     var isActive: Boolean = true
 ) : BaseEntity() {

src/main/kotlin/kr/co/vividnext/sodalive/v2/recommend/application/RecommendedCreatorFollowService.kt

@@ -0,0 +1,51 @@
+package kr.co.vividnext.sodalive.v2.recommend.application
+
+import kr.co.vividnext.sodalive.common.SodaException
+import kr.co.vividnext.sodalive.member.Member
+import kr.co.vividnext.sodalive.member.MemberRepository
+import kr.co.vividnext.sodalive.member.following.CreatorFollowing
+import kr.co.vividnext.sodalive.member.following.CreatorFollowingRepository
+import org.springframework.stereotype.Service
+import org.springframework.transaction.annotation.Transactional
+
+@Service
+class RecommendedCreatorFollowService(
+    private val memberRepository: MemberRepository,
+    private val creatorFollowingRepository: CreatorFollowingRepository
+) {
+    @Transactional
+    fun followCreators(member: Member, creatorIds: List<Long>) {
+        val distinctCreatorIds = creatorIds.distinct()
+        val creatorById = distinctCreatorIds
+            .filter { it != member.id }
+            .associateWith { creatorId ->
+                memberRepository.findCreatorByIdOrNull(creatorId)
+                    ?: throw SodaException(messageKey = "member.validation.creator_not_found")
+            }
+
+        distinctCreatorIds.forEach { creatorId ->
+            if (creatorId == member.id) {
+                return@forEach
+            }
+
+            val existingFollowing = creatorFollowingRepository.findByCreatorIdAndMemberId(
+                creatorId = creatorId,
+                memberId = member.id!!
+            )
+            if (existingFollowing != null) {
+                if (!existingFollowing.isActive) {
+                    existingFollowing.isNotify = true
+                    existingFollowing.isActive = true
+                }
+                return@forEach
+            }
+
+            creatorFollowingRepository.save(
+                CreatorFollowing().apply {
+                    this.member = member
+                    creator = creatorById.getValue(creatorId)
+                }
+            )
+        }
+    }
+}