左外连接LINQ To Entities

Question

我有以下实体：

客户
- ClientID
- ClientName

承包商
- 承包商ID
- ContractorName

PreferredContractors
- PreferredContractorID
- ClientID
- 承包商ID

所以我有一份客户和承包商名单。客户更愿意与某些承包商合作。我想构建一个LINQ to Entity查询，该查询使用一个布尔字段来提取所有承包商，指示承包商是否是首选。

 public IQueryable<PreferredContractor> GetPreferredContractors(int clientID)
    {
        var preferredContractors = from c in db.Contractors
                  from pc in db.PreferredContractors.DefaultIfEmpty()
                  select new PreferredContractor
                             {
                                 ContractorID = c.ContractorID,
                                 ContractorName = c.ContractorName,
                                 IsPreferred = // This is where I need help
                             };

        return preferredContractors;
    }

如何判断承包商是否优先？

Answer 1

    var preferredContractors =
              from c in db.Contractors
              join pc in db.PreferredContractors.Where(pc2 => pc2.ClientId == clientId) on c.ContractorId equals pc.ContractorId into j
              from pc in j.DefaultIfEmpty()
              select new PreferredContractor
                         {
                             ContractorID = c.ContractorID,
                             ContractorName = c.ContractorName,
                             IsPreferred = pc != null
                         };