4.3. Implementation of Infrastructure Layer

Implementing RepositoryImpl is carried out in infrastructure layer.

RepositoryImpl implements the method defined in Repository interface.

4.3.1. Implementing RepositoryImpl

Methods to create a Repository for relational database using MyBatis3 and JPA are introduced below.

4.3.1.1. Implementing Repository using MyBatis3

When MyBatis3 is to be used as persistence API with relational database, RepositoryImpl need not be implemented, if Repository interface is created using “Mapper interface mechanism” provided by MyBatis3.

This is because it is a mechanism where MyBatis3 automatically maps the method of Mapper interface and the statement (SQL) to be called.

When using MyBatis3, an application developer creates:

  • Repository interface (method definition)
  • Mapping file (SQL and O/R mapping definition)
An example of creating Repository interface and mapping file is given below.
For details on how to use MyBatis3, refer to: Database Access (MyBatis3).
  • An example of creating Repository interface (Mapper interface)
package com.example.domain.repository.todo;

import com.example.domain.model.Todo;

// (1)
public interface TodoRepository {
    // (2)
    Todo findOne(String todoId);
}
Sr. No. Description
(1)

Create as an interface of POJO.

It is not necessary to specify MyBatis3 interface, annotation, etc.
(2)

Define a method of Repository.

Basically it is not necessary to assign MyBatis3 annotation; however, annotation may also be specified in some cases.
  • An example of creating mapping file
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- (3) -->
<mapper namespace="com.example.domain.repository.todo.TodoRepository">

    <!-- (4) -->
    <select id="findOne" parameterType="string" resultMap="todoResultMap">
      SELECT
          todo_id,
          title,
          finished
      FROM
          t_todo
      WHERE
          todo_id = #{todoId}
    </select>

    <!-- (5) -->
    <resultMap id="todoResultMap" type="Todo">
        <result column="todo_id" property="todoId" />
        <result column="title" property="title" />
        <result column="finished" property="finished" />
    </resultMap>

</mapper>
Sr. No. Description
(3)

Create a mapping file for each Repository interface.

Specify FQCN (Fully Qualified Class Name) of Repository interface in namespace of mapping file (namespace attribute of mapper element).
(4)

Define statement (SQL) to be run for each method defined in Repository interface.

Specify a method name of Repository interface in statement ID of each statement element (id attribute of select/insert/update/delete element).
(5)

When a query is to be raised, define O/R mapping as required.

Auto mapping can be used for simple O/R mapping; however, individual mapping definition is needed for complex O/R mapping.

In the above example, auto mapping can also be used for mapping definition as it is simple O/R mapping.

4.3.1.2. Implementing Repository using JPA

When JPA is to be used as persistence API with relational database, Repository can be very easily created if org.springframework.data.jpa.repository.JpaRepository of Spring Data JPA is used.
For details on how to use Spring Data JPA, refer to Database Access (JPA).
When Spring Data JPA is used, only an interface with inherited JpaRepository is required to be created for basic CRUD operations. In other words, RepositoryImpl is not required.
However, RepositoryImpl is needed for using dynamic query (JPQL).
Refer to Database Access (JPA) for implementing RepositoryImpl when using Spring Data JPA.
  • TodoRepository.java
public interface TodoRepository extends JpaRepository<Todo, String> { // (1)
    // ...
}
Sr. No. Description
(1)
 Only by defining the interface that inherits JpaRepository, basic CRUD operations for Todo entity can be performed without being implemented.
Describe the case to add operations which are not provided by JpaRepository.
When Spring Data JPA is used, if it is a static query, it is advisable to add a method to the interface and to specify the query (JPQL) to be executed when that method is called, using the annotation.
  • TodoRepository.java
public interface TodoRepository extends JpaRepository<Todo, String> {
    @Query("SELECT COUNT(t) FROM Todo t WHERE finished = :finished") // (1)
    long countByFinished(@Param("finished") boolean finished);
    // ...
}
Sr. no. Description
(1)
 Specify a query (JPQL) using @Query annotation.