linq - 实体框架查询中的使用方法

Question

反正有这个错误吗？我想在其他查询中重用相同的 Lamba 表达式，而不是重复。LinqKit 或其他 linq 表达式可以做到这一点吗？

错误

LINQ to Entities 无法识别方法 'Boolean GetEvent(Tournaments.Data.Entities.Event, System.String)' 方法，并且此方法无法转换为存储表达式。

代码

public MobileEventDetailModel GetDetails(string applicationId)
{
    var @event = (from e in _eventsRepository.DataContext.Events.Include(q => q.Assets.Select(a => a.Asset))
                  where GetEvent(e, applicationId)
                select new
                    {
                        e.Id,
                        e.EventParent.Name,
                        LogoId = (from a in e.Assets
                                     where a.Type   == EventAssetType.Logo
                                     select a.AssetId).FirstOrDefault()
                    }).FirstOrDefault();

    return new MobileEventDetailModel
        {
            Id = @event.Id,
            Name = @event.Name,
            Logo = string.Format("{0}{1}{2}", Config.BaseUrl, Config.ImagesPath, @event.LogoId)
        };
}

public bool GetEvent(Event @event, string applicationId)
{

    return @event.Active && @event.Visible && @event.MobileEventApplications.Any(m =>
                          m.MobileApplication.ApplicationId == applicationId &&
                          (!m.MobileApplication.ActivationLength.HasValue || EntityFunctions.AddDays(DateTime.Now, 1) < EntityFunctions.AddMonths(m.MobileApplication.DateActivated, m.MobileApplication.ActivationLength.Value)));
}

Answer 1

您需要使用表达式：

public MobileEventDetailModel GetDetails(string applicationId)
{

    var event = _eventsRepository.DataContext.Events.Include(q => q.Assets.Select(a => a.Asset))
                .Where(GetEvent(applicationId))
                .Select(a =>  new
                    {
                        a.Id,
                        a.EventParent.Name,
                        LogoId = (from b in a.Assets
                                     where b.Type == EventAssetType.Logo
                                     select b.AssetId).FirstOrDefault()
                    }).FirstOrDefault();

    return new MobileEventDetailModel
        {
            Id = event.Id,
            Name = event.Name,
            Logo = string.Format("{0}{1}{2}", Config.BaseUrl, Config.ImagesPath, event.LogoId)
        };
}

public Expression<Func<Event, bool>> GetEvent(int applicationId)
{
    return = a => a.Active 
                  && a.Visible 
                  && a.MobileEventApplications
                      .Any(m => m.MobileApplication.ApplicationId == applicationId 
                                && (!m.MobileApplication.ActivationLength.HasValue 
                                    || EntityFunctions.AddDays(DateTime.Now, 1) 
                                       < EntityFunctions
                                         .AddMonths(m.MobileApplication.DateActivated, m.MobileApplication.ActivationLength.Value)
                                   )
                      );
}

更新：抱歉，那天晚上很晚，希望更改后的版本更符合您的要求。