在 linq 中使用日期时间值搜索时如何更改日期时间值？

Question

我使用此搜索功能时出现一些错误。我有两个表：员工和出勤。在表

Attendance

中有

AddendanceDate

（日期时间）列。我想得到今天缺席员工名单的结果。对于

DateTime.Today

结果还可以，但我想选择其他日期的搜索关键字。

如何在以下代码中进行分配？

public async Task<IEnumerable<AbsentReportsViewModel>> GetAllAbsentEmpAsync(DateTime date)
{
     var query = await (from e in _dbContext.Employees
                        join attt in _dbContext.Attendances
                             on e.Id equals attt.EmployeeId into eGroup
                        from eattt in eGroup.Where(a => a.AttendanceDate == DateTime.Today ).DefaultIfEmpty()
                        where eattt.AttendanceDate == null
                        select new AbsentReportsViewModel
                               {
                                   JobId = e.JobId,
                                   EmpReportName = e.NameMM,
                                   DeptId = e.DeptId,
                                   RankId = e.CurrentRankId,
                                   DeptReportName = e.Department.DeptName,
                                   RankReportName = e.Rank.RankName,
                                   BarCode = e.Barcode,
                                   EmpReportId = e.Id,
                               }).ToListAsync();

    return query;
}

我试过了：

... a.AttendanceDate == date.DefaultIfEmpty(),

... a.AttendanceDate == ((date).Year, (date).Month, (date).Day).DefaultIfEmpty()

我没有得到想要的结果。

请帮我看看路。谢谢！

Answer 1

为了确保日期属于当前日期，最好使用范围过滤器。它将强制 SQL Server 使用索引。

LEFT JOIN

表示也可以简化：

var startDate = DateTime.Today.Date;
var endDate = startDate.AddDays(1);

var query = 
    from e in _dbContext.Employees
    from eattt in _dbContext.Attendances
        .Where(a => a.EmployeeId == e.Id && a.AttendanceDate >= startDate && a.AttendanceDate < endDate)
        .DefaultIfEmpty()
    where eattt.AttendanceDate == null
    select new AbsentReportsViewModel
    {
        JobId = e.JobId,
        EmpReportName = e.NameMM,
        DeptId = e.DeptId,
        RankId = e.CurrentRankId,
        DeptReportName = e.Department.DeptName,
        RankReportName = e.Rank.RankName,
        BarCode = e.Barcode,
        EmpReportId = e.Id,
    };