Question

数据库中有三个相关的表。倡导者，供应商和Advocate_Vendor。

Advocate_Vendor表是多对多链接，有一个vendorId和一个advocateId。

我的最终目标是找回一个List<Advocate>对象......一组属于一个供应商的拥护者。我写了这个：

var list = new List<Advocate>();

        foreach (var vendorAdvocates in db.Advocate_Vendors)
        {
            if (vendorAdvocates.VendorId == vendorId)
            {
                list.Add(db.Advocates.SingleOrDefault(a => a.AdvocateId == vendorAdvocates.AdvocateId));
            }
        }

然后这个：

var list = (from vendorAdvocates in db.Advocate_Vendors 
            where vendorAdvocates.VendorId == vendorId 
            select db.Advocates.SingleOrDefault(a => 
                a.AdvocateId == vendorAdvocates.AdvocateId)).ToList();

这是最好的方法吗？似乎错了，比如可能有更简化的方法来使用'contains'关键字或看起来更具可读性的东西......得到所有供应商的拥护者

感谢

Answer 1

在Advocate_Vendors和Advocates之间使用join将是正确的方法。

var list = (from vendorAdvocates in db.Advocate_Vendors 
            join advocates in db.Advocates
               on vendorAdvocates.AdvocateId equals advocates.AdvocateId
            where vendorAdvocates.VendorId == vendorId
            select advocates).ToList();

Answer 2

var list = (from vendorAdvocates in db.Advocate_Vendors
            from advocate in db.Advocates
            where vendorAdvocates.VendorId == vendorId && 
                  vendorAdvocates.AdvocateId = advocate.Id
            select advocate)
           .ToList();

Answer 3

如果你正确设置外键和导航属性，应该可以这样写，或类似的东西：

var list = (from vendorAdvocates in db.Advocate_Vendors 
            where vendorAdvocates.VendorId == vendorId 
            select db.Advocate).ToList();

选择...的最佳方式在哪里使用linq

3 个答案: