EF6-> EFCore 3.1左外部联接

Question

我正在评估从EF6升级到EFCore 3.1的过程，并且陷入了简单的左外部联接中。我们有大量的代码，例如以下“

                IQueryable<SearchItemResponseDataModel> items = from item in db.Item
                                                            from e in db.Ingredient.Where(a => item.ItemId == a.ItemId).DefaultIfEmpty()
                                                            select new SearchItemResponseDataModel
                                                            {
                                                                ItemId = item.ItemId,
                                                                Name = item.Name,
                                                                IsActive = item.IsActive,
                                                                Description = item.Description,
                                                                Color = e.Color
                                                            };

在EF6中工作正常；但是，在EFCore中，我收到以下异常：

系统的方法'System.Linq.IQueryable 1[Dal.Ingredient]' cannot be used for parameter of type 'Microsoft.EntityFrameworkCore.DbSet 1 [Dal.Ingredient]'的类型为'Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable 1[Dal.Ingredient] Where[Ingredient](Microsoft.EntityFrameworkCore.DbSet 1 [Dal.Ingredient]'的表达式。 Linq.Expressions.Expression 1[System.Func 2 [Dal.Ingredient，System.Boolean]]）'

如果我像下面这样重写它，它将运行没有问题：

                IQueryable<SearchItemResponseDataModel> items = from item in db.Item
                                                            join e in db.Ingredient on item.ItemId equals e.ItemId into ef
                                                            from e in ef.DefaultIfEmpty()
                                                            select new SearchItemResponseDataModel
                                                            {
                                                                ItemId = item.ItemId,
                                                                Name = item.Name,
                                                                IsActive = item.IsActive,
                                                                Description = item.Description,
                                                                Color = e.Color
                                                            };

所以，这似乎是由于System.Linq和Microsoft.EntityFrameworkCore之间的命名空间冲突引起的。

我添加了

public static class DbSetExtensions
{
    public static IAsyncEnumerable<TEntity> AsAsyncEnumerable<TEntity>(this Microsoft.EntityFrameworkCore.DbSet<TEntity> obj) where TEntity : class
    {
        return Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.AsAsyncEnumerable(obj);
    }

    public static IQueryable<TEntity> Where<TEntity>(this Microsoft.EntityFrameworkCore.DbSet<TEntity> obj, System.Linq.Expressions.Expression<Func<TEntity, bool>> predicate) where TEntity : class
    {
        return System.Linq.Queryable.Where(obj, predicate);
    }
}

根据这里的建议，进入我班级的基础：https://github.com/dotnet/efcore/issues/18220

如果我删除此替代项，则该方法有效：

IQueryable<SearchItemResponseDataModel> items = from item in db.Item.AsQueryable()
                                                        from e in db.Ingredient.AsQueryable().Where(a => item.ItemId == a.ItemId).DefaultIfEmpty()
                                                        select new SearchItemResponseDataModel
                                                        {
                                                            ItemId = item.ItemId,
                                                            Name = item.Name,
                                                            IsActive = item.IsActive,
                                                            Description = item.Description,
                                                            Color = e.Color
                                                        };

最好有一个覆盖，所以我不需要到处都添加.AsQueryable（）：（