Add repositories

ServerSide/src/main/java/com/letter/server/dao/repository/MessageRepository.java

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+package com.letter.server.dao.repository;
+
+import com.letter.server.dao.entity.MessageEntity;
+import com.letter.server.dao.entity.UserEntity;
+import org.springframework.data.repository.CrudRepository;
+
+import java.util.List;
+
+public interface MessageRepository extends CrudRepository<MessageEntity, Long> {
+
+    List<MessageEntity> findAllBySenderAndRecipient(UserEntity sender, UserEntity recipient);
+
+    List<MessageEntity> findAllBySenderInAndRecipientIn(UserEntity sender, UserEntity recipient);
+}

ServerSide/src/main/java/com/letter/server/dao/repository/OnlineStatusRepository.java

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+package com.letter.server.dao.repository;
+
+import com.letter.server.dao.entity.OnlineStatusEntity;
+import org.springframework.data.repository.CrudRepository;
+
+public interface OnlineStatusRepository extends CrudRepository<OnlineStatusEntity, Long> {
+}

ServerSide/src/main/java/com/letter/server/dao/repository/UserRepository.java

@@ -0,0 +1,10 @@
+package com.letter.server.dao.repository;
+
+import com.letter.server.dao.entity.UserEntity;
+import org.springframework.data.repository.CrudRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface UserRepository extends CrudRepository<UserEntity, Long> {
+
+}