如何从嵌套的 select 查询 linq 中读取数据

Question

我有一个像下面这样的 linq 类型的查询。

var querymiangin = (from t1 in _context.Apiapplicant
                    join t2 in _context.ApiApplicantHistory on t1.Id equals t2.ApiApplicantId
                    join t3 in _context.EntityType on t2.LastReqStatus equals t3.Id
                    where t1.IsDeleted == false && t1.LastRequestStatus == t2.Id && t3.Name == "granted"
                    select new { A = t1, B = t2, Year = t1.ApiRequestDate.Substring(0, 4), Month = t1.ApiRequestDate.Substring(5, 2) } into joined
                    group joined by new { joined.Year, joined.Month, joined.B.LastReqStatus } into grouped
                    select grouped.Select(g => new { ApiReqDate = g.A.ApiRequestDate, ApiDate = g.B.Date, ApiLastReqStatus = g.B.LastReqStatus, ApiYear = g.Year, ApiMonth = g.Month })).ToList();

在select部分，ApiReqDate和ApiDate有多个记录。现在我的问题是每个月组和年组，我有多个 ApiDate 和 ApiReqDate 记录，我希望每个组都基于条件 (t1.LastRequestStatus == t2.Id && t3.Name == "granted") 通过GetPersianDaysDiffDate()方法，获取每个月ApiReqDate与其相关ApiDate记录的差值，然后求出当月的平均值。

为此，我编写了如下代码：

var avgDateDiff = querymiangin.DefaultIfEmpty()
       .GroupBy(x => new { x.ApiYear, x.ApiMonth }, (key, g) => new
       {
           key.ApiYear,
           key.ApiYear,
           Avg = g.Average(y => GetPersianDaysDiffDate(y.ApiReqDate,y.ApiDate))
       })
       .ToList();

但问题是每个参数 x.ApiYear、x.ApiMonth、y.ApiReqDate、y.ApiDate 都是未知的，它显示错误。如果有人可以建议我解决这个问题，我将不胜感激。

Answer 1

1 - 对于第一个请求 querymiangin，您不需要 group by 语句，只需将代码更改为 :

var querymiangin = (from t1 in Apiapplicant
                    join t2 in ApiApplicantHistory on t1.Id equals t2.ApiApplicantId
                    join t3 in EntityType on t2.LastReqStatus equals t3.Id
                    where t1.IsDeleted == false && t1.LastRequestStatus == t2.Id && t3.Name == "granted"
                    select new
                    {
                        ApiReqDate = t1.ApiRequestDate,
                        ApiDate = t2.Date,
                        ApiYear = t1.ApiRequestDate.Substring(0, 4),
                        ApiMonth = t1.ApiRequestDate.Substring(5, 2)
                    }).ToList();

2 - 对于第二个查询 avgDateDiff，通过 ApiYear 和 ApiMonth 使用 GroupBy 并计算 Average，例如：

var avgDateDiff = querymiangin
       .GroupBy(x => new { x.ApiYear, x.ApiMonth }, (key, g) => new
       {
           key.ApiYear,
           key.ApiMonth,
           Avg = g.Average(y => GetPersianDaysDiffDate(y.ApiReqDate, y.ApiDate))
       }).ToList();

希望对您有所帮助。

如何从嵌套的 select 查询 linq 中读取数据

How to read data from a nested select query linq

linq

asp.net-core

ef-core-3.0