使用 Ef core 3.1 从 Db 获取相关数据

Question

我试图从 2 个相关的 table 中查询数据，但是（EfCore 3.1 中没有 groupJoin）结果为空，因为相关的 table 没有项目。我正在使用 mvc 核心 3.1 和 EF 核心 3。代码

    var vmq =
       from req in  _context.Set<QuettaReq>()
               .Where(sd => sd.SiteUserId == _userManager.GetUserId(User) && sd.QuettaClose == false)
                .OrderBy(d => d.ApplicationDate).ThenBy(c => c.Category.CatName)  ///Results should be =1 could be many

       from offers in _context.Set<QuettaOffer>().Where(id => id.QuettaOfferId == req.Id)
           .OrderBy(p => p.OfferPrice) //Results Should be 0 could be many 


       select new {  req,offers,};
        //Results are Empty When it should be ==1 req , 0 offers 

       var combinVm = vmq.Select(t => new ReqOferQestionAnswerVm //ReqOferQestionAnswerVm==Just parameters from 2 tables 
        {
            ReqText = t.req.ReqText,
         //Pram..
        }).ToList();

        return View(combinVm);

我不明白如果 2 table 有 0 个结果洞查询是 0 怎么办。

我的类长得像

 public class QuettaReq
{
    public QuettaReq()
    {
        QuettaOffer = new List<QuettaOffer>();
    }

    [Key] public int Id { get; set; }

    //Pram
    public virtual List<QuettaOffer> QuettaOffer { get; set; }
}

public class QuettaOffer
{
    public QuettaOffer()
    {
    }

    [Key] public   int       QuettaOfferId { get; set; }
    public virtual QuettaReq QuettaReq     { get; set; }
    public         int       QuettaReqId   { get; set; }
}

Answer 1

事实上你做了 Inner Join 而不是 Left Join。

改成这样：

var vmq =
   from req in  _context.Set<QuettaReq>()
           .Where(sd => sd.SiteUserId == _userManager.GetUserId(User) && sd.QuettaClose == false)
            .OrderBy(d => d.ApplicationDate).ThenBy(c => c.Category.CatName)  ///Results should be =1 could be many

   join offers in _context.Set<QuettaOffer>().OrderBy(p => p.OfferPrice)
      on req.Id equals offers.QuettaReqId into Joff
   from offers in Joff.DefaultIfEmpty()


   select new {  req,offers,};

使用 Ef core 3.1 从 Db 获取相关数据

getting related data from Db with Ef core 3.1

c#

entity-framework

linq-to-sql

.net-core

ef-core-3.1