Question

这很奇怪，任何人都可以试着解释一下为什么这样做很好：

_db.Tasks.Include(t => t.Category).ThenInclude(c => c.ApplicationUser)
                .ToList();

虽然这会引发异常：

_db.Tasks.Include(t=>t.Category).ThenInclude(c=>c.ApplicationUser)
                .Where(t => t.Category.ApplicationUser.UserName == username)
                .ToList();

由于某种原因.Include（）不适用于.Where子句。有什么想法吗？

例外：

   at lambda_method(Closure , InternalEntityEntry )
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.SimpleNonNullableDependentKeyValueFactory`1.TryCreateFromCurrentValues(InternalEntityEntry entry, TKey& key)
   at Microsoft.EntityFrameworkCore.Query.Internal.WeakReferenceIdentityMap`1.CreateIncludeKeyComparer(INavigation navigation, InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryBuffer.IncludeCore(Object entity, INavigation navigation)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryBuffer.Include(QueryContext queryContext, Object entity, IReadOnlyList`1 navigationPath, IReadOnlyList`1 relatedEntitiesLoaders, Int32 currentNavigationIndex, Boolean queryStateManager)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryBuffer.Include(QueryContext queryContext, Object entity, IReadOnlyList`1 navigationPath, IReadOnlyList`1 relatedEntitiesLoaders, Boolean queryStateManager)
   at Microsoft.EntityFrameworkCore.Query.Internal.GroupJoinInclude.Include(Object entity)
   at Microsoft.EntityFrameworkCore.Query.QueryMethodProvider.<_GroupJoin>d__26`4.MoveNext()
   at System.Linq.Enumerable.<SelectManyIterator>d__163`3.MoveNext()
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.<_TrackEntities>d__15`2.MoveNext()
   at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at _:line 56

生成的sql在针对Sql Server执行时工作得很好：

SELECT [t].[TaskId], [t].[CategoryId], [t].[Description], [t].[Name], [t].[Timestamp], [t.Category].[CategoryId], [t.Category].[Description], [t.Category].[Name], [t.Category].[Timestamp], [t.Category].[UserId], [t.Category.ApplicationUser].[Id], [t.Category.ApplicationUser].[AccessFailedCount], [t.Category.ApplicationUser].[ConcurrencyStamp], [t.Category.ApplicationUser].[Email], [t.Category.ApplicationUser].[EmailConfirmed], [t.Category.ApplicationUser].[LockoutEnabled], [t.Category.ApplicationUser].[LockoutEnd], [t.Category.ApplicationUser].[NormalizedEmail], [t.Category.ApplicationUser].[NormalizedUserName], [t.Category.ApplicationUser].[PasswordHash], [t.Category.ApplicationUser].[PhoneNumber], [t.Category.ApplicationUser].[PhoneNumberConfirmed], [t.Category.ApplicationUser].[SecurityStamp], [t.Category.ApplicationUser].[TwoFactorEnabled], [t.Category.ApplicationUser].[UserName], [c].[CategoryId], [c].[Description], [c].[Name], [c].[Timestamp], [c].[UserId], [a].[Id], [a].[AccessFailedCount], [a].[ConcurrencyStamp], [a].[Email], [a].[EmailConfirmed], [a].[LockoutEnabled], [a].[LockoutEnd], [a].[NormalizedEmail], [a].[NormalizedUserName], [a].[PasswordHash], [a].[PhoneNumber], [a].[PhoneNumberConfirmed], [a].[SecurityStamp], [a].[TwoFactorEnabled], [a].[UserName]
FROM [Tasks] AS [t]
INNER JOIN [Categories] AS [t.Category] ON [t].[CategoryId] = [t.Category].[CategoryId]
LEFT JOIN [AspNetUsers] AS [t.Category.ApplicationUser] ON [t.Category].[UserId] = [t.Category.ApplicationUser].[Id]
INNER JOIN [Categories] AS [c] ON [t].[CategoryId] = [c].[CategoryId]
LEFT JOIN [AspNetUsers] AS [a] ON [c].[UserId] = [a].[Id]
ORDER BY [t.Category].[UserId]

型号：

public class Task
{
    [Key]
    public int TaskId { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public DateTime Timestamp { get; set; }
    public int CategoryId { get; set; }

    public virtual Category Category { get; set; }
}

public class Category
{
    [Key]
    public int CategoryId { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public DateTime Timestamp { get; set; }

    public string UserId { get; set; }
    [ForeignKey("UserId")]
    public virtual ApplicationUser ApplicationUser { get; set; }

    public virtual ICollection<Task> Tasks { get; set; }
}

public class ApplicationUser : IdentityUser
{
    public virtual ICollection<Category> Categories { get; set; }
}

Answer 1

最后，我浪费了半天后才能解决问题。我无法使用.Include（）和.Where（）获得所需的结果，但这对我有用。如果你找到一种方法可以使用它，请告诉我.Include（）和.Where（），因为我很好奇：

return _db.Tasks
                    .Where(t => t.Category.ApplicationUser.UserName == username)
                    .Select(t => new
                    {
                        t,
                        t.Category
                    })
                    .AsEnumerable()
                    .Select(t => t.t)
                    .ToList();

包含（）的Wheres子句失败

1 个答案: