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MyBatis-Plus條件構造器select方法返回指定字段

條件構造器select用法

1.返回特定的幾個字段 select(字段…)

2.排除某幾個字段 select(entiyClass,predicate判斷)

3.分組聚合函數 select(“聚合函數”)

搭配service的.listMaps方法,將返回的數據封裝到map中

避免了多余字段的返回

實例

實例一：

public AjaxResult listAll(ProjectBuild projectBuild) {
    //只返回了id和name兩個字段    
    List<Map<String,Object>> list = this.iProjectBuildService.listMaps(
            WrAppers.lambdaQuery(projectBuild).select(ProjectBuild::getBuildId,ProjectBuild::getBuildName).orderByAsc(ProjectBuild::getBuildId)
    );

    return AjaxResult.success(list);
}
 

示例2

@Test
public void selectByQueryWrapper8(){
    QueryWrapper<Employee> queryWrapper=new QueryWrapper();
 
    queryWrapper.lambda()
             .select(Employee.class,fieldInfo->!fieldInfo.getColumn().equals("birthday")&&!fieldInfo.getColumn().equals("gender"))
             .gt(Employee::getSalary,3500)
             .like(Employee::getName,"小");
    List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
    System.out.println(employeeList);
}

示例3

期望的效果是：

SELECT departmentId,AVG(salary) AS avg_salary FROM t_employee GROUP BY department_id;

如下實現

@Test
public void selectByQueryWrapper9(){
    QueryWrapper<Employee> queryWrapper=new QueryWrapper();
  
    queryWrapper.lambda()
             .select(Employee::getDepartmentId,"AVG(salary) AS avg_salary")
             .groupBy(Employee::getDepartmentId);
    List<Employee> employeeList = employeeMapper.selectList(queryWrapper);
    System.out.println(employeeList);
}

問題解決

問題描述: map中的key沒有使用駝峰命名

解決方法: 使用hutool工具包中的 MapUtil.toCamelCaseMap(map);

//處理map中key未駝峰命名
list = list.stream().map(MapUtil::toCamelCaseMap).collect(Collectors.toList());