LINQ ToListAsync表达式与DbSet

Question

我编写了一个C＃MVC5 Internet应用程序，并对使用.ToListAsync LINQ表达式有疑问。

这是我在Index操作结果中工作的代码：

IEnumerable<IMapLocationItem> mapLocationImageGalleries = await db.mapLocationImageGalleries.Where(m => m.userName.Equals(userName)).ToListAsync();
IEnumerable<IMapLocationItem> mapLocationVideoGalleries = await db.mapLocationVideoGalleries.Where(m => m.userName.Equals(userName)).ToListAsync();
IEnumerable<IMapLocationItem> mapLocationItemsCombined = mapLocationImageGalleries.Concat(mapLocationVideoGalleries);

我想为上面的代码创建一个服务函数。 这是我编码的内容：

public async Task<IEnumerable<IMapLocationItem>> GetAllMapLocationItemsFromUserName(string userName)
{
    IEnumerable<IMapLocationItem> mapLocationImageGalleries = await db.mapLocationImageGalleries.Where(m => m.userName.Equals(userName)).ToListAsync();
    IEnumerable<IMapLocationItem> mapLocationVideoGalleries = await db.mapLocationVideoGalleries.Where(m => m.userName.Equals(userName)).ToListAsync();
    IEnumerable<IMapLocationItem> mapLocationItemsCombined = mapLocationImageGalleries.Concat(mapLocationVideoGalleries);
    return mapLocationItemsCombined;
}

我收到以下错误：

Error   17  'System.Linq.IQueryable<CanFindLocation.Models.MapLocationItems.MapLocationImageGallery>' does not contain a definition for 'ToListAsync' and no extension method 'ToListAsync' accepting a first argument of type 'System.Linq.IQueryable<CanFindLocation.Models.MapLocationItems.MapLocationImageGallery>' could be found (are you missing a using directive or an assembly reference?)

完全相同的代码在Index操作结果中工作正常，但在服务方法中却没有。 为什么这样，我怎么能让这个工作？

提前致谢

Answer 1

如注释中所述， using System.Data.Entity （在Entity Framework包下）添加以获取QueryableExtensions 。

对于.NET Core，这些方法位于Microsoft.EntityFrameworkCore