05_Mybatis-Plus_ActiveRecord(活动记录)

Active Record(活动记录)，是一种领域模型模式，特点是一个模型类对应关系型数据库中的一个表，而模型类的一个实例对应表中的一条记录。

ActiveRecord一直广受动态语言（PHP、Ruby等）的喜爱，而Java作为准静态语言，对于ActiveRecord往往只能感叹其优雅，所以MP也在AR道路上进行了一定的探索。

如何使用AR模式

仅仅需要让实体类继承Model类并且实现主键指定方法即可。

相关代码：

public class Employee extends Model<Employee> {
	/**
	 * 该方法是Model的抽象方法 必须要实现
	 * 这里用来指定当前实体类的主键属性
	 */
	@Override
	protected Serializable pkVal() {
		return this.id;
	}
}

继承Model
实现pkVal，返回主键

AR基本的CRUD操作

插入操作

public boolean insert()

相关代码：

/**
 * AR插入操作
 * @throws Exception
 */
@Test
public void testARInsert() throws Exception {
  Employee emp = new Employee();
  emp.setLastName("Tommy");
  emp.setEmail("[email protected]");
  emp.setAge(35);
  boolean result = emp.insert();
  System.out.println("result: "+result);
}

日志输出：

DEBUG 06-09 13:36:01,570 ==>  Preparing: INSERT INTO tbl_employee ( last_name, email, age ) VALUES ( ?, ?, ? )  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:36:01,618 ==> Parameters: Tommy(String), [email protected](String), 35(Integer) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:36:01,623 <==    Updates: 1 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

result: true

修改操作

public boolean updateById()

相关代码：

/**
 * AR修改操作
 * @throws Exception
 */
@Test
public void testARUpdate() throws Exception {
  Employee emp = new Employee();
  emp.setAge(15);
  emp.setId(16);
  boolean result = emp.updateById();
  System.out.println("result: "+result);
}

日志输出：

DEBUG 06-09 13:40:05,772 ==>  Preparing: UPDATE tbl_employee SET age=? WHERE id=?  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:40:05,830 ==> Parameters: 15(Integer), 16(Integer) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:40:05,832 <==    Updates: 1 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

result: true

查询操作

public T selectById()

相关代码：

/**
 * AR查询，根据id
 * @throws Exception
 */
@Test
public void testARSelectById() throws Exception {
  Employee emp = new Employee();
  emp.setId(16);
  Employee employee = emp.selectById();
  System.out.println(employee);
}

日志输出：

DEBUG 06-09 13:42:30,910 ==>  Preparing: SELECT id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE id=?  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:42:30,964 ==> Parameters: 16(Integer) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:42:30,984 <==      Total: 1 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

Employee [id=16, lastName=Tommy, [email protected], gender=1, age=15]

public T selectById(Serializable id)

相关代码：

/**
 * AR查询，根据id,直接传入id值
 * @throws Exception
 */
@Test
public void testARSelectByIdSerializable() throws Exception {
  Employee emp = new Employee();
  Employee employee = emp.selectById(16);
  System.out.println(employee);
}

日志输出：

DEBUG 06-09 13:44:32,941 ==>  Preparing: SELECT id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE id=?  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:44:32,979 ==> Parameters: 16(Integer) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:44:32,996 <==      Total: 1 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

Employee [id=16, lastName=Tommy, [email protected], gender=1, age=15]

public List selectAll()

相关代码：

/**
 * AR查询，查询所有记录ALL
 * @throws Exception
 */
@Test
public void testARSelectAll() throws Exception {
  Employee emp = new Employee();
  List<Employee> emps = emp.selectAll();
  System.out.println(emps);
}

日志输出：

DEBUG 06-09 13:46:25,544 ==>  Preparing: SELECT id,last_name AS lastName,email,gender,age FROM tbl_employee  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:46:25,598 ==> Parameters:  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:46:25,626 <==      Total: 9 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

[
  Employee [id=1, lastName=Tom, [email protected], gender=1, age=22],
  Employee [id=2, lastName=Jerry, [email protected], gender=0, age=25],
  Employee [id=3, lastName=Black, [email protected], gender=1, age=30],
  Employee [id=4, lastName=White, [email protected], gender=0, age=35],
  Employee [id=8, lastName=Ken, [email protected], gender=1, age=30],
  Employee [id=12, lastName=Ken, [email protected], gender=1, age=30],
  Employee [id=13, lastName=Marry, [email protected], gender=0, age=15],
  Employee [id=15, lastName=1老师, [email protected], gender=0, age=20],
  Employee [id=16, lastName=Tommy, [email protected], gender=1, age=15]
]

public List selectList(Wrapper wrapper)

相关代码：

/**
 * AR查询，selectList，可以传入查询对象Wrapper
 * @throws Exception
 */
@Test
public void testARSelectList() throws Exception {
  Employee emp = new Employee();
  List<Employee> emps = emp.selectList(new EntityWrapper<Employee>().like("last_name", "Ken"));
  System.out.println(emps);
}

日志输出：

DEBUG 06-09 13:49:32,255 ==>  Preparing: SELECT id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (last_name LIKE ?)  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:49:32,322 ==> Parameters: %Ken%(String) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:49:32,357 <==      Total: 2 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

[
  Employee [id=8, lastName=Ken, [email protected], gender=1, age=30],
  Employee [id=12, lastName=Ken, [email protected], gender=1, age=30]
]

public int selectCount(Wrapper wrapper)

相关代码：

/**
 * AR查询：selectCount
 * @throws Exception
 */
@Test
public void testARSelectCount() throws Exception {
  Employee emp = new Employee();
  int count = emp.selectCount(new EntityWrapper<Employee>().like("last_name", "K"));
  System.out.println("count: "+count);
}

日志输出：

DEBUG 06-09 13:51:55,245 ==>  Preparing: SELECT COUNT(1) FROM tbl_employee WHERE (last_name LIKE ?)  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:51:55,313 ==> Parameters: %K%(String) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 13:51:55,332 <==      Total: 1 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

count: 3

删除操作

注意，当删除不存在的数据时，也会返回true。

public boolean deleteById()

相关代码：

/**
 * AR删除：根据id删除——从对象setId
 * @throws Exception
 */
@Test
public void testARDeleteById() throws Exception {
  Employee emp = new Employee();
  emp.setId(15);
  boolean result = emp.deleteById();
  System.out.println("result: "+result);
}

日志输出：

DEBUG 06-09 14:07:16,965 ==>  Preparing: DELETE FROM tbl_employee WHERE id=?  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 14:07:17,010 ==> Parameters: 15(Integer) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 14:07:17,013 <==    Updates: 1 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

result: true

public boolean deleteById(Serializable id)

相关代码：

/**
 * AR删除：根据id删除——直接传入id值
 * @throws Exception
 */
@Test
public void testARDeleteByIdSerializable() throws Exception {
  Employee emp = new Employee();
  boolean result = emp.deleteById(13);
  System.out.println("result: "+result);
}

日志输出：

DEBUG 06-09 14:08:43,546 ==>  Preparing: DELETE FROM tbl_employee WHERE id=?  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 14:08:43,594 ==> Parameters: 13(Integer) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 14:08:43,596 <==    Updates: 1 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

result: true

public boolean delete(Wrapper wrapper)

相关代码：

/**
 * AR删除：根据条件删除
 * @throws Exception
 */
@Test
public void testARDeleteWrapper() throws Exception {
  Employee emp = new Employee();
  boolean result = emp.delete(new EntityWrapper<Employee>().like("age", "15"));
  System.out.println("result: "+result);
}

日志输出：

DEBUG 06-09 14:09:19,046 ==>  Preparing: DELETE FROM tbl_employee WHERE (age LIKE ?)  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 14:09:19,124 ==> Parameters: %15%(String) (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 14:09:19,126 <==    Updates: 1 (JakartaCommonsLoggingImpl.java:54)

控制台输出：

result: true

分页复杂操作

这里会返回Page对象，需要getRecords()才能得到具体数据，其他是分页结果等信息。

public Page selectPage(Page page,String whereClause, Object...args).getRecords();

相关代码：

/**
 * AR分页复杂操作
 * @throws Exception
 */
@Test
public void testSelectPage() throws Exception {
  Employee emp = new Employee();
  Page<Employee> emps = emp.selectPage(new Page<Employee>(2, 1), new EntityWrapper<Employee>().eq("last_name", "Ken"));
  System.out.println(emps);
  System.out.println(emps.getRecords());
}

日志输出：

DEBUG 06-09 14:19:42,949 ==>  Preparing: SELECT id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (last_name = ?)  (JakartaCommonsLoggingImpl.java:54)
DEBUG 06-09 14:19:43,024 ==> Parameters: Ken(String) (JakartaCommonsLoggingImpl.java:54)

控制台输出：

Page:{ [Pagination { total=0 ,size=1 ,pages=0 ,current=2 }], records-size:1 }
[Employee [id=12, lastName=Ken, [email protected], gender=1, age=30]]

AR总结

AR模式提供了一种更加便捷的方式实现了CRUD操作，其本质还是调用了Mybatis对应的方法（sqlSession调用方法），类似于语法糖。

语法糖：计算机学专家发明的一种术语。指计算机语言中添加的某种语法，这种语法对原本语言的功能并没有影响，可以更方便开发者使用，可以避免出错的机会，让程序可读性更好。

到此，我们简单领略了Mybatis-Plus的魅力与高效率，值得一提的是：我们提供了强大的代码生成器，可以快速生成各类代码，真正做到了即开即用。

目录CONTENT

05_Mybatis-Plus_ActiveRecord(活动记录)

05_Mybatis-Plus_ActiveRecord(活动记录)

如何使用AR模式

AR基本的CRUD操作

插入操作

public boolean insert()

修改操作

public boolean updateById()

查询操作

public T selectById()

public T selectById(Serializable id)

public List selectAll()

public List selectList(Wrapper wrapper)

public int selectCount(Wrapper wrapper)

删除操作

public boolean deleteById()

public boolean deleteById(Serializable id)

public boolean delete(Wrapper wrapper)

分页复杂操作

public Page selectPage(Page page,String whereClause, Object...args).getRecords();

AR总结

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