Convert to Nullable in a group key throws ArgumentException (regression in 3.0-preview7)

[AlekseyMartynov]

Microsoft.EntityFrameworkCore.SqlServer version 3.0.0-preview7.19362.6

The query below runs fine with EF Core 2.x.

Code to reproduce

class Program {
    static void Main(string[] args) {
        using(var db = new MyContext()) {
            var query = db.Set<MyClass1>()
                .GroupBy(obj => new { I0 = (int?)obj.Date.Value.Year }) // HERE
                .OrderBy(g => g.Key.I0)
                .Select(g => new {
                    I0 = g.Count(),
                    I1 = g.Key.I0
                });

            var data = query.ToArray();
        }
    }
}

public class MyClass1 {
    public int ID { get; set; }
    public DateTime? Date { get; set; }
}

public class MyContext : DbContext {
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) {
        if(!optionsBuilder.IsConfigured)
            optionsBuilder.UseSqlServer(...);
    }
    protected override void OnModelCreating(ModelBuilder modelBuilder) {
        modelBuilder.Entity<MyClass1>();
    }
}

Exception

System.ArgumentException
  HResult=0x80070057
  Message= Argument type 'System.Int32' does not match the corresponding member type 'System.Nullable`1[System.Int32]' 
  Source=System.Linq.Expressions
  StackTrace:
   at System.Linq.Expressions.Expression.ValidateNewArgs(ConstructorInfo constructor, ReadOnlyCollection`1& arguments, ReadOnlyCollection`1& members)
   at System.Linq.Expressions.Expression.New(ConstructorInfo constructor, IEnumerable`1 arguments, IEnumerable`1 members)
   at System.Linq.Expressions.NewExpression.Update(IEnumerable`1 arguments)
   at Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.RelationalQueryableMethodTranslatingExpressionVisitor.TranslateGroupBy(ShapedQueryExpression source, LambdaExpression keySelector, LambdaExpression elementSelector, LambdaExpression resultSelector)
   at Microsoft.EntityFrameworkCore.Query.Pipeline.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.RelationalQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Pipeline.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.RelationalQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Pipeline.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.RelationalQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Pipeline.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass9_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetEnumerator()
   at System.Collections.Generic.LargeArrayBuilder`1.AddRange(IEnumerable`1 items)
   at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Program.Main(String[] args) in s:\temp\ConsoleApp1\ConsoleApp1\Program.cs:line 16

[smitpatel]

Need to wrap convert nodes in TranslateGroupingKey method to match types in client side code. (also necessary changes when the grouping key is used to plug into Sql tree)

[smitpatel]

poaching.