當前上下文中不存在名稱“covid”

Question

嗨，我將 sql 查詢轉換為 linq 我收到了這個錯誤。 當我刪除 group by 時也不例外，但我應該使用 group by。 為什么我得到這個例外？

public List<BiontechSinovacCovidDto> GetBiontechSinovacCovidDto()
{
    using(SirketDBContext context=new SirketDBContext())
    {
        var result = 
            from asi in context.Asilar
            join covid in context.Covids
                on asi.CovidId equals covid.CovidId
            group asi by asi.AsiIsmi into isim
            select new BiontechSinovacCovidDto
            {
                AsiIsmi=isim.Key,
    //exception    OrtalamaCovidSuresi=(EF.Functions.DateDiffDay(covid.CovidYakalanmaTarih, covid.CovidBitisTarih)).Average()
            };
        return result.ToList();                                              
    }
}

我的 sql 查詢

Select 
    AsiIsmi,
    AVG(Cast(DATEDIFF(Day,CovidYakalanmaTarih, CovidBitisTarih)AS FLOAT)) as OrtalamaCovidSuresi 
From Asilar 
    INNER JOIN Covids on Covids.CovidId=Asilar.CovidId 
group by AsiIsmi

|AsiIsmi| OrtalamaCovidSuresi|
-------  ------------------
Biontech      13.6667
Sinovac        15

BiontechSinovacCovidDto

public class BiontechSinovacCovidDto
{
    public string AsiIsmi { get; set; }
    public double OrtalamaCovidSuresi { get; set; }
}

Answer 1

Average具有接受 lambda 的過載。 你必須使用這個版本。 在這種情況下，您還必須對covid進行分組。

public List<BiontechSinovacCovidDto> GetBiontechSinovacCovidDto()
{
    using (var context = new SirketDBContext())
    {
        var result = 
            from asi in context.Asilar
            join covid in context.Covids
                on asi.CovidId equals covid.CovidId
            group covid by asi.AsiIsmi into isim
            select new BiontechSinovacCovidDto
            {
                AsiIsmi = isim.Key,
                OrtalamaCovidSuresi = isim.Average(x => EF.Functions.DateDiffDay(x.CovidYakalanmaTarih, x.CovidBitisTarih))
            };

        return result.ToList();                                              
    }
}