Question

我使用Entity Framework-6。我有这个代码（outter join，LINQ to entity）：

        var inspectionSitesConjection = (from st in sites
                                         join ir in inspectionReview on st.Id equals ir.SiteId into g
                                         from subsite in g.DefaultIfEmpty()
                                         select new GeneralReportViewModel
                                         {
                                             siteName = subsite.Site.Name,
                                             address = subsite.Site.Description,
                                             inspectionDate = subsite.DateReview,
                                             siteType = subsite.Site.SiteType.Description,
                                             frequency = subsite.InspectionFrequency.Name,
                                             status = subsite.IsNormal,
                                         }).AsNoTracking();

我需要按siteName和frequency分组。

在LINQ里面制作小组是不是很容易？

Answer 1

这是一个起点：

var grouped = inspectionSitesConjection
    .GroupBy(item => new { item.siteName, item.frequency });

但请注意，结果（正如您在Queryable.GroupBy文档中看到的）不再是IQueryable<GeneralReportViewModel>，而是IQueryable<IGrouping<Key, GeneralReportViewModel>>其中Key是具有siteName的匿名类型和frequency属性。

我提供这个只是因为你特别要求。你用这个查询想要实现的目标并不十分清楚。此外，一旦您决定使用显式连接，则使用联接表而不是导航属性，并考虑由于外连接subsite可以为null。

from st in sites
join ir in inspectionReview on st.Id equals ir.SiteId into g
from subsite in g.DefaultIfEmpty()
select new GeneralReportViewModel
{
    siteName = st.Name,
    address = st.Description,
    siteType = st.SiteType.Description,
    inspectionDate = subsite.DateReview, // problem if subsite == null
    frequency = subsite.InspectionFrequency.Name, // problem if subsite == null
    status = subsite.IsNormal, // problem if subsite == null
})

在outter中加入LINQ到实体

1 个答案: