Use method in entity framework query

问题

Is there anyway around this error? I'd like to reuse the same lamba expression in other queries instead of having duplication. Can LinqKit or other linq expression do this?

Error

LINQ to Entities does not recognize the method 'Boolean GetEvent(Tournaments.Data.Entities.Event, System.String)' method, and this method cannot be translated into a store expression.

Code

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)));
}

回答1:

You need to use an Expression:

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)
                                   )
                      );
}

Update: Sorry it was late the other night, the changed version is hopefully more what you were looking for.

来源：https://stackoverflow.com/questions/19761632/use-method-in-entity-framework-query

标签

linq

entity-framework

lambda

entity-framework-6