Result of left joining a nullable nominal type should be null (i.e. no instance) and not an instance with all null property values

when Blog does not have a Post, following query does not work in 5.0.0-preview.8.* or 6.0.0-* nightly. but works in 5.0.0-preview.7.*

 public class Blog
    {
        public int BlogId { get; set; }
        public string Url { get; set; }

        [NotMapped]
        public Post Post { get; set; }

        public List<Post> Posts { get; set; } = new List<Post>();
    }

    public class Post
    {
        public int PostId { get; set; }

        public string Title { get; set; }

        public string Content { get; set; }

        public int BlogId { get; set; }

        public Blog Blog { get; set; }
    }

// this IQueryable would come from other API.

 var dbPosts = from p in db.Posts
                          // select p;
                         select new Post
                         {
                             PostId = p.PostId,
                             BlogId = p.BlogId,
                             Content = p.Content
                         };

 var query = from blog in db.Blogs
                    join post in dbPosts on blog.BlogId equals post.BlogId into posts
                    from xpost in posts.DefaultIfEmpty()
                    select new Blog
                    {
                         Url = blog.Url,
                         Post = xpost
                   };

Steps to reproduce

I have a repo to reproduce the bug.

https://github.com/skclusive/EFLeftJoinBug

Unhandled exception. System.InvalidOperationException: Nullable object must have a value.
   at lambda_method17(Closure , QueryContext , DbDataReader , ResultContext , SingleQueryResultCoordinator )
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()

Further technical details

EF Core version:
Database provider: (e.g. Microsoft.EntityFrameworkCore.Sqlite)
Target framework: (e.g. .NET Core 5.0)
Operating system:
IDE: (e.g. Visual Studio Code)

Confirmed this works in 3.1, but fails in latest daily, on SQL Server and SQLite.

@ajcvickers

@ajcvickers - What is the generated SQL? Can you post query plan?

@smitpatel

@smitpatel Here's the logs:

dbug: Microsoft.EntityFrameworkCore.Query[10111]
      Compiling query expression: 
      'DbSet<Blog>()
          .GroupJoin(
              inner: DbSet<Post>()
                  .Select(p => new Post{ 
                      PostId = p.PostId, 
                      BlogId = p.BlogId, 
                      Content = p.Content 
                  }
                  ), 
              outerKeySelector: blog => blog.BlogId, 
              innerKeySelector: post => post.BlogId, 
              resultSelector: (blog, posts) => new { 
                  blog = blog, 
                  posts = posts
               })
          .SelectMany(
              collectionSelector: <>h__TransparentIdentifier0 => <>h__TransparentIdentifier0.posts
                  .DefaultIfEmpty(), 
              resultSelector: (<>h__TransparentIdentifier0, xpost) => new Blog{ 
                  Url = <>h__TransparentIdentifier0.blog.Url, 
                  Post = xpost 
              }
          )'
dbug: Microsoft.EntityFrameworkCore.Query[10107]
      queryContext => new SingleQueryingEnumerable<Blog>(
          (RelationalQueryContext)queryContext, 
          RelationalCommandCache.SelectExpression(
              Projection Mapping:
                  Url -> 0
                  Post.PostId -> 1
                  Post.BlogId -> 2
                  Post.Content -> 3
              SELECT b.Url, p.PostId, p.BlogId, p.Content
              FROM Blogs AS b
              LEFT JOIN Posts AS p ON b.BlogId == p.BlogId), 
          Func<QueryContext, DbDataReader, ResultContext, SingleQueryResultCoordinator, Blog>, 
          EFLeftJoinBug.BloggingContext, 
          False, 
          False
      )
dbug: Microsoft.EntityFrameworkCore.Database.Command[20103]
      Creating DbCommand for 'ExecuteReader'.
dbug: Microsoft.EntityFrameworkCore.Database.Command[20104]
      Created DbCommand for 'ExecuteReader' (0ms).
dbug: Microsoft.EntityFrameworkCore.Database.Connection[20000]
      Opening connection to database 'Test' on server '(local)'.
dbug: Microsoft.EntityFrameworkCore.Database.Connection[20001]
      Opened connection to database 'Test' on server '(local)'.
dbug: Microsoft.EntityFrameworkCore.Database.Command[20100]
      Executing DbCommand [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT [b].[Url], [p].[PostId], [p].[BlogId], [p].[Content]
      FROM [Blogs] AS [b]
      LEFT JOIN [Posts] AS [p] ON [b].[BlogId] = [p].[BlogId]
info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (7ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT [b].[Url], [p].[PostId], [p].[BlogId], [p].[Content]
      FROM [Blogs] AS [b]
      LEFT JOIN [Posts] AS [p] ON [b].[BlogId] = [p].[BlogId]
fail: Microsoft.EntityFrameworkCore.Query[10100]
      An exception occurred while iterating over the results of a query for context type 'EFLeftJoinBug.BloggingContext'.
      System.InvalidOperationException: Nullable object must have a value.
         at lambda_method(Closure , QueryContext , DbDataReader , ResultContext , SingleQueryResultCoordinator )
         at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
System.InvalidOperationException: Nullable object must have a value.
   at lambda_method(Closure , QueryContext , DbDataReader , ResultContext , SingleQueryResultCoordinator )
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
Unhandled exception. System.InvalidOperationException: Nullable object must have a value.
   at lambda_method(Closure , QueryContext , DbDataReader , ResultContext , SingleQueryResultCoordinator )
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
   at EFLeftJoinBug.Program.Main(String[] args) in /home/ajcvickers/AllTogetherNow/Daily/Daily.cs:line 43

SingleQueryResultCoordinator is not the error. We are probably trying to materialize null into something which is non-nullable which should have been skipped from materialization.

Note: This gave incorrect result in 3.1.x by initialize post with default values rather than returning null (the result of DefaultIfEmpty).

With #20633 fixed, it now throws error.

Right fix would be not to create instance if no rows matched.

Follow up work after #38479:

All are sub-cases of the umbrella #22517 unless noted.

Second join applied after the left join, then whole-object projection (shaper rebuilt → marker lost). Repro: closed dup EF Core materializes projection property as object with default values #26873.
GroupBy applied after the left join, then whole-object projection (shaper rebuilt via ApplyGrouping). Repro: closed dup DefaultIfEmpty() unsupported in subquery when main query has group by? #28119.
Plain inner with no pushdown (no aggregate/filter) via the LeftJoin operator — marker is inlined into the combined SELECT and never becomes NULL. (no dedicated issue) → Tracked in Query: whole non-entity object from a plain (non-aggregated) LeftJoin/DefaultIfEmpty inner is not nulled on no-match #38608; not fixed as part of this work. The stated mechanism is a misdiagnosis: nav-expansion folds the plain inner Select into the pending selector, so the marker is never injected (not "inlined"). It can't be fixed in the relational layer — deferred to the nav-expansion rework (Consider removing nav expansion as a way to tackle the pending selector problem #32957 / Rearchitect navigation expansion to happen in translation, not preprocessing #37859).
Value-type struct / record struct whole-object projection (members not defaulted; materialization throws).
Constructor-bound DTO / positional record struct / ValueTuple whole-object projection (fails at translation — a distinct path).
Overlaps GroupJoin throws when applied on an anonymous return type output of another Linq #28248.
Union / set-operation of two left-join non-entity projections (set-operation translation failure). (no dedicated issue)
Server-side obj == null / obj != null on a left-joined non-entity, in Where / OrderBy (translation failure). A complete Result of left joining a nullable nominal type should be null (i.e. no instance) and not an instance with all null property values #22517 (true null-tracking) would likely enable this. (no dedicated issue)
RightJoin where the outer (non-entity) side is the nullable one — the marker is injected for the inner side only, so this still throws.
Nullable<T> whole-object projection (latent and currently unreachable; the gate skips on IsValueType, but default(T?) is null).

Make the dotnet#30915 nullability marker survive a subsequent join

Default a value-type non-entity left-join projection to default(T) on…

Address PR feedback: fix marker comments and add SqlServer SQL baselines

Default a value-type non-entity left-join projection to default(T) on…

Fold ValueTuple/Tuple member access through constructor-bound project…

Make the nullability marker survive GroupBy-element to-one subquery l…

Address review: guard non-grouping subquery clone, encapsulate marker…

Make the nullability marker survive GroupBy-element to-one subquery l…

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Result of left joining a nullable nominal type should be null (i.e. no instance) and not an instance with all null property values #22517

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Result of left joining a nullable nominal type should be null (i.e. no instance) and not an instance with all null property values #22517

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Steps to reproduce

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ajcvickers commented on Sep 12, 2020

smitpatel commented on Sep 13, 2020

ajcvickers commented on Sep 13, 2020

smitpatel commented on Sep 14, 2020

smitpatel commented on Sep 14, 2020

77 remaining items

ajcvickers commented on Jun 27, 2026

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