带有 DbSet 的 LINQ ToListAsync 表达式

Question

我编写了一个 C# MVC5 Internet 应用程序，并且有一个关于使用 .ToListAsync LINQ 表达式的问题。

这是我在索引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。这是我的编码：

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 操作结果中可以正常工作，但在服务方法中却不行。为什么会这样？我怎样才能让它发挥作用？

提前致谢

Answer 1

如 cmets 中所述，添加 using System.Data.Entity（在实体框架包下）以获取 QueryableExtensions。

对于.NET Core，这些方法在Microsoft.EntityFrameworkCore下