如何将SQL查询转换为LINQ？

Posted 2021-05-02

如何将以下SQL查询转换为linq？这是经过尝试的

    SELECT COUNT(DISTINCT SampleDateTime) AS Total
    FROM dbo.PrecisionArchive
    WHERE AgencySourceId = 7 AND EventType IN('R', 'ONS')

答案

你可以使用：

var total = dbo.PrecisionArchive.Where(p => p.AgencySourceId == 7)
                                .Where(p => p.EventType == "R" || p.EventType == "ONS")
                                .Select(p => p.SampleDateTime)
                                .Distinct()
                                .Count();

另一答案

这样的事情应该有效：

var result = 
    (from x in dbContext.PrecisionArchive
     where x.AgencySource == 7 &&
           (x.EventType == "R" || x.EventType == "ONS")
     select x.SampleDateTime)
    .Distinct()
    .Count();

您也可以尝试使用Contains来表示IN子句，但我不相信Linq-to-SQL支持它：

var result = 
    (from x in dbContext.PrecisionArchive
     where x.AgencySource == 7 &&
           new[] { "R", "ONS" }.Contains(x.EventType)
     select x.SampleDateTime)
    .Distinct()
    .Count();