c# - 抽象/虚拟方法的通用返回类型

Question

我有两个基类之间的关系:

public abstract class RecruiterBase<T>
{
  // Properties declare here
  // Constructors declared here

  public abstract IQueryable<T> GetCandidates();
}

public abstract class CandidateBase<T>
{
  // Properties declare here
  // Constructors declared here
}

以及它们的具体实现:

public class CandidateA : CandidateBase<CandidateA>
{
  // Constructors declared here
}

public class RecruiterA : RecruiterBase<RecruiterA>
{
  // Constructors declared here

  // ----HERE IS WHERE I AM BREAKING DOWN----
  public override IQueryable<CandidateA> GetCandidates()
  {
     return from c in db.Candidates
            where c.RecruiterId == this.RecruiterId
            select new CandidateA
            {
              CandidateId = c.CandidateId,
              CandidateName = c.CandidateName,
              RecruiterId = c.RecruiterId
            };
  }
}

根据 MSDN 文档 http://msdn.microsoft.com/en-us/library/ms379564%28VS.80%29.aspx (大约下降了一半)以及关于 SO 的类似(但不相同)问题 Specifying the return type of an abstract method from a Base Class according to a Sub Class

我可以对重写方法 GetCandidates 的返回类型使用我的 concreate 实现，但这不是我想要的，我想使用不同抽象类的具体实现。这是父/子数据库关系。我想要实现的目标是可能的吗？我目前收到编译时错误，我的 GetCandidates 返回类型不匹配。

谢谢

Answer 1

看起来您需要定义多个泛型类型，其中一个可能被限制为从 CandidateBase 派生。

尝试这样的事情:

public abstract class RecruiterBase<T, C> where C : CandidateBase
{
  // Properties declare here
  // Constructors declared here

  public abstract IQueryable<C> GetCandidates();
}

public abstract class CandidateBase<T>
{
  // Properties declare here
  // Constructors declared here
}

public class CandidateA : CandidateBase<CandidateA>
{
  // Constructors declared here
}

public class RecruiterA : RecruiterBase<RecruiterA, CandidateA>
{
  public override IQueryable<CandidateA> GetCandidates()
  {
     return from c in db.Candidates
            where c.RecruiterId == this.RecruiterId
            select new CandidateA
            {
              CandidateId = c.CandidateId,
              CandidateName = c.CandidateName,
              RecruiterId = c.RecruiterId
            };
  }
}

编辑包括克里斯的更正