MyBatisPlus系列五：条件构造器EntityWrapper

EntityWrapper 简介
1、 MybatisPlus 通过 EntityWrapper（简称 EW，MybatisPlus 封装的一个查询条件构造器）或者 Condition（与 EW 类似） 来让用户自由的构建查询条件，简单便捷，没有额外的负担， 能够有效提高开发效率。
2、实体包装器，主要用于处理 sql 拼接，排序，实体参数查询等。
3、注意: 使用的是数据库字段，不是 Java 属性。
4、条件参数说明:

测试查询：

@Test
public void testEntityWrapperSelect() {
	//我们需要分页查询tbl_employee表中，年龄在18~50之间且性别为男且姓名为Tom的所有用户
	List emps =employeeMapper.selectPage(new Page(1, 2),
				new EntityWrapper()
				.between("age", 18, 50)
				.eq("gender", 1)
				.eq("last_name", "Tom")
			);
	System.out.println(emps);
	
	//我们需要分页查询tbl_employee表中，年龄在18~50之间且性别为男且姓名为Tom的所有用户
	List emps3 = employeeMapper.selectPage(
					new Page(1,2),
						Condition.create()
						.between("age", 18, 50)
						.eq("gender", "1")
						.eq("last_name", "Tom")
						);
	System.out.println(emps3);
		
	// 查询tbl_employee表中， 性别为女并且名字中带有"老师" 或者  邮箱中带有"a"
	List emps1 = employeeMapper.selectList(
			new EntityWrapper()
			.eq("gender", 0)
			.like("last_name", "老师")
			//.or()    // SQL: (gender = ? AND last_name LIKE ? OR email LIKE ?)
			.orNew()   // SQL: (gender = ? AND last_name LIKE ?) OR (email LIKE ?)
			.like("email", "a")
			);
	System.out.println(emps1);

	//查询性别为女的, 根据age进行排序(asc/desc), 简单分页
	List emps2  = employeeMapper.selectList(
			new EntityWrapper()
			.eq("gender", 0)
			.orderBy("age") //默认是升序
			//.orderDesc(Arrays.asList(new String [] {"age"}))
			.last("desc limit 1,3") //在sql最后拼接
			);
	System.out.println(emps2);
}

控制台输出：

selectPage方法：
Preparing: SELECT id AS id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (age BETWEEN ? AND ? AND gender = ? AND last_name = ?)
Parameters: 18(Integer), 50(Integer), 1(Integer), Tom(String) 
Total: 1
[Employee [id=1, lastName=Tom, [email protected], gender=1, age=22]]
selectPage使用Condition：
Preparing: SELECT id AS id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (age BETWEEN ? AND ? AND gender = ? AND last_name = ?) 
Parameters: 18(Integer), 50(Integer), 1(String), Tom(String)
Total: 1
[Employee [id=1, lastName=Tom, [email protected], gender=1, age=22]]
selectList使用or：
Preparing: SELECT id AS id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (gender = ? AND last_name LIKE ? OR email LIKE ?)
Parameters: 0(Integer), %老师%(String), %a%(String)
Total: 3
[Employee [id=1, lastName=Tom, [email protected], gender=1, age=22], Employee [id=2, lastName=Jerry, [email protected], gender=0, age=25], Employee [id=7, lastName=王五, [email protected], gender=0, age=null]]
selectList使用orNew：
Preparing: SELECT id AS id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (gender = ? AND last_name LIKE ?) OR (email LIKE ?)
Parameters: 0(Integer), %老师%(String), %a%(String)
Total: 3
[Employee [id=1, lastName=Tom, [email protected], gender=1, age=22], Employee [id=2, lastName=Jerry, [email protected], gender=0, age=25], Employee [id=7, lastName=王五, [email protected], gender=0, age=null]]
selectList使用orderBy：
Preparing: SELECT id AS id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (gender = ?) ORDER BY age
Parameters: 0(Integer)
Total: 2
[Employee [id=7, lastName=王五, [email protected], gender=0, age=null], Employee [id=2, lastName=Jerry, [email protected], gender=0, age=25]]
selectList使用orderDesc：
Preparing: SELECT id AS id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (gender = ?) ORDER BY age DESC
Parameters: 0(Integer)
Total: 2 
[Employee [id=2, lastName=Jerry, [email protected], gender=0, age=25], Employee [id=7, lastName=王五, [email protected], gender=0, age=null]]
selectList使用last：
Preparing: SELECT id AS id,last_name AS lastName,email,gender,age FROM tbl_employee WHERE (gender = ?) ORDER BY age desc limit 1,3 
Parameters: 0(Integer)
Total: 1
[Employee [id=7, lastName=王五, [email protected], gender=0, age=null]]

测试修改：

@Test
public void testEntityWrapperUpdate() {
	Employee employee = new Employee();
	employee.setLastName("王五");
	employee.setEmail("[email protected]");
	employee.setGender(0);
	employeeMapper.update(employee,
				new EntityWrapper()
				.eq("last_name", "Tom")
				.eq("age", 44)
				);
}

控制台输出：

Preparing: UPDATE tbl_employee SET last_name=?, email=?, gender=? WHERE (last_name = ? AND age = ?) 
Parameters: 王五(String), [email protected](String), 0(Integer), Tom(String), 44(Integer)  
Updates: 0

测试删除：

@Test
public void testEntityWrapperDelete() {
	employeeMapper.delete(
				new EntityWrapper()
				.eq("last_name", "Tom")
				.eq("age", 22)
			);
}

控制台输出：

Preparing: DELETE FROM tbl_employee WHERE (last_name = ? AND age = ?)   
Parameters: Tom(String), 22(Integer)
Updates: 1