Query: System.ArgumentException: must be reducible node when using ternary operator

[mb2140]

Steps to reproduce

Trying to run this query which works in EF6 (I don't believe this is a duplicate because other issues involved a "group-by" clause):

PlatformDTO dto = UnitOfWork.Projects.Find()
     .Where(x => x.ID== id).Select(x => new PlatformDTO()
                {
                    ID = x.ID,
                    User = new PlatformUserDTO()
                    {
                             Score = x.User != null ? x.User.Score : 0,
                             UserID = x.User != null ? x.User.ID : 0,
                    }.FirstOrDefault();

{System.ArgumentException: must be reducible node
at System.Linq.Expressions.Expression.ReduceAndCheck()
at System.Linq.Expressions.Expression.ReduceExtensions()
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExtensionExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteVariableAssignment(BinaryExpression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteAssignBinaryExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteBlockExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExtensionExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteConditionalExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.MemberAssignmentRewriter..ctor(MemberAssignment binding, StackSpiller spiller, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.BindingRewriter.Create(MemberBinding binding, StackSpiller spiller, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteMemberInitExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.MemberAssignmentRewriter..ctor(MemberAssignment binding, StackSpiller spiller, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.BindingRewriter.Create(MemberBinding binding, StackSpiller spiller, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteMemberInitExpression(Expression expr, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack)
at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression1 lambda) at System.Linq.Expressions.Compiler.StackSpiller.RewriteLambdaExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression node) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression node) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression node) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.Add(Expression node) at System.Linq.Expressions.Compiler.StackSpiller.ChildRewriter.AddArguments(IArgumentProvider expressions) at System.Linq.Expressions.Compiler.StackSpiller.RewriteMethodCallExpression(Expression expr, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpression(Expression node, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.RewriteExpressionFreeTemps(Expression expression, Stack stack) at System.Linq.Expressions.Compiler.StackSpiller.Rewrite[T](Expression1 lambda)
at System.Linq.Expressions.Compiler.LambdaCompiler.Compile(LambdaExpression lambda)
at System.Linq.Expressions.Expression1.Compile(Boolean preferInterpretation) at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateExecutorLambda[TResults]() at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateQueryExecutor[TResult](QueryModel queryModel) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass19_01.b__0()
at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)

EF Core version: (found in project.json or packages.config)
Operating system:
Visual Studio version: (e.g. VS 2013 or n/a)

Other details about my project setup:

[maumar]

@mb2140 can you also provide the model you are using? Specifically, contents of OnModelCreating method on your DbContext and the entities involved: Project, User.

[candoumbe]

@maumar
Hi,

I ran into the same issues with a somewhat "basic" query

var doctors = dbContext.Doctors.Select(x => new DoctorInfo
                        {
                            Firstname = x.Firstname,
                            Lastname = x.Lastname,
                            Id = x.UUID,
                            SpecialtyId = x.Specialty != null ? x.Specialty.UUID : (Guid?)null,
                            UUID = x.UUID,
                            UpdatedDate = x.UpdatedDate
                        })

which throws the exception @mb2140 described.

The workaround I found for now is to use no ternary condition in the select clause

var doctors = dbContext.Doctors.Select(x => new DoctorInfo
                        {
                            Firstname = x.Firstname,
                            Lastname = x.Lastname,
                            Id = x.UUID,
                            //SpecialtyId = x.Specialty != null ? x.Specialty.UUID : (Guid?)null, // this is the line that causes the exception to be thrown
                            UUID = x.UUID,
                            UpdatedDate = x.UpdatedDate
                        })

I hope this will help

[maumar]

This works in the current bits and produces the following sql:

SELECT [x].[FirstName], [x].[LastName], [x].[UUID], CASE
	WHEN [x].[SpecialtyUUID] IS NOT NULL
	THEN [x.Specialty].[UUID] ELSE NULL
END, [x].[UpdatedDate]
FROM [Doctors] AS [x]
LEFT JOIN [Speciality] AS [x.Specialty] ON [x].[SpecialtyUUID] = [x.Specialty].[UUID]

[ole1986]

I am getting the exact error message "must be reducible node" when using EF Core 2.1.1 with AspNetCore 2.1.1

The statement is pretty basic, too

var pendingArticles = ctx.ArticleTable.AsNoTracking()
                                            .Where(p => p.InheritedTable.Status <= 1)
                                            .Where(p => items.Select(p => p.ID).Contains(p.InheritedTableID))
                                            .GroupBy(p => p.ArticleID)
                                            .Select(p => new { p.Key, Qty = p.Sum(a => a.Qty) })
                                            .ToList();

UPDATED (WORKAROUND)

I finally fixed it

.Where(p => !items.Select(p => p.ID).Contains(p.InheritedTableID)); // causes the error

var Ids = items.Select(p => p.ID);
.Where(p => Ids.Contains(p.InheritedTableID)); // fixed it

So, the nested .Select(...) is the evildoer