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05_Mybatis-Plus_ActiveRecord(活动记录)

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2021-06-09 / 0 评论 / 0 点赞 / 6,699 阅读 / 8,013 字 / 正在检测是否收录...
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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;
	}
}
  1. 继承Model
  2. 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("tommy@tomxwd.top");
  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), tommy@tomxwd.top(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=tommy@tomxwd.top, 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=tommy@tomxwd.top, 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=tom@tomxwd.top, gender=1, age=22],
  Employee [id=2, lastName=Jerry, email=jerry@tomxwd.top, gender=0, age=25],
  Employee [id=3, lastName=Black, email=black@tomxwd.top, gender=1, age=30],
  Employee [id=4, lastName=White, email=white@tomxwd.top, gender=0, age=35],
  Employee [id=8, lastName=Ken, email=ken@tomxwd.top, gender=1, age=30],
  Employee [id=12, lastName=Ken, email=ken@tomxwd.top, gender=1, age=30],
  Employee [id=13, lastName=Marry, email=marry@tomxwd.top, gender=0, age=15],
  Employee [id=15, lastName=1老师, email=laoshi@tomxwd.top, gender=0, age=20],
  Employee [id=16, lastName=Tommy, email=tommy@tomxwd.top, 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=ken@tomxwd.top, gender=1, age=30],
  Employee [id=12, lastName=Ken, email=ken@tomxwd.top, 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=ken@tomxwd.top, gender=1, age=30]]


AR总结

  1. 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。
  1. 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
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