Question

在下面的QueryableEntities方法中， IEnumerable<Competition>.AsQueryable()将返回无法返回的IQueryable<Competition>，因为它期待IQueryable<T>

我只能写一种方法来返回IQueryable<Competition>和IQueryable<Submission>

如果有人知道怎么做，请告诉我，谢谢

public partial class WinBoutsDataContext<T> : System.Data.Linq.DataContext where T : class
{
    public IQueryable<T> QueryableEntities
    {
        get
        {
            if (typeof(T).Equals(typeof(Model.Competition)))
            {
                return this.ConvertToCompetitionList(
                      this.GetTable<Storage.Competition>()).AsQueryable();
            }
             else if(typeof(T).Equals(typeof(Model.Submission)))
            {
                return this.ConvertToSubmissionList(
                       this.GetTable<Storage.CompetitionEntry>()).AsQueryable();
            }
        }
    }

    public DataAccess.Model.Competition ConvertToCompetition(DataAccess.Storage.Competition comp)
    {

        DataAccess.Model.Competition modelComp = new DataAccess.Model.Competition 
        { 
            CompetitionID = comp.CompetitionID, 
            Active = comp.Active, 
            CompetitionStatusID = 
            comp.CompetitionStatusID, 
            Duration = comp.Duration, 
            EndDate = comp.EndDate, 
            Entrants = comp.Entrants, 
            Featured = comp.Featured, 
            Image = comp.Image, 
            IsOvertime = comp.IsOvertime, 
            MaxEntrants = comp.MaxEntrants, 
            Notes = comp.Notes, 
            OvertimeDuration = comp.OvertimeDuration, 
            OvertimeEnd = comp.OvertimeEnd, 
            OvertimeStart = comp.OvertimeStart, 
            ParentCompetitionID = comp.ParentCompetitionID, 
            Prize = comp.Prize, StartDate = comp.StartDate, 
            SuggestedBy = comp.SuggestedBy, 
            Summary = comp.Summary, 
            Title = comp.Title 
        };

        return modelComp;
    }

    public IEnumerable<DataAccess.Model.Competition> ConvertToCompetitionList(IEnumerable<DataAccess.Storage.Competition> compList)
    {
        List<DataAccess.Model.Competition> compModelList = new List<DataAccess.Model.Competition>();

        foreach (DataAccess.Storage.Competition comp in compList)
        {
            compModelList.Add(ConvertToCompetition(comp));
        }

        return compModelList;
    }
}

Answer 1

同意Adrian对设计原则的评论，但是如果你想这样做的话

public IQueryable<T> QueryableEntities
{
    get
    {
        if (typeof(T).Equals(typeof(Model.Competition)))
        {
            return this.ConvertToCompetitionList(
                  this.GetTable<Storage.Competition>()).AsQueryable() as IQueryable<T>;
        }
         else if(typeof(T).Equals(typeof(Model.Submission)))
        {
            return this.ConvertToSubmissionList(
                   this.GetTable<Storage.CompetitionEntry>()).AsQueryable() as IQueryable<T>;
        }
    }
}

将编译并运行正常。 x as IQueryable<T>如果可以投放x，则IQueryable<T>投放到null，如果不投，则Model.Competition投放IQueryable<Model.Competition>。

注意：这意味着当您构建通用类时，如果它具有类型Model.Submission，它将返回IQueryable<Model.Submission>，如果它具有类型null，它将返回{{1}}，并将为任何其他类型返回{{1}}。

Answer 2

通常最好不要概括。很多开发人员似乎花了很多时间试图让一个属性/方法/类做很多事情，但它违背了许多面向对象的原则。就个人而言，我只会使用2个属性，可能称为Competitions，另一个Submissions。与QueryableEntities相比，它的意图要多得多。

是否可以将IQueryable <someclass>返回给IQueryable <t>方法？</t> </someclass>

2 个答案: