Validate that all leaves in the entity types hierarchy are concrete

[anpete]

Model:

    public class StarWarsContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            => optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=GrephQL.StarWars;Trusted_Connection=True;");

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Character>();
        }
    }

    public abstract class Character
    {
        public string Id { get; set; }
        public string Name { get; set; }
    }

    public class Human : Character
    {
        public string HomePlanet { get; set; }
    }

    public class Droid : Character
    {
        public string PrimaryFunction { get; set; }
    }

Query:

data.Set<Character>().SingleAsync(h => h.Id == "3");

Error:

An exception of type 'System.IndexOutOfRangeException' occurred in Microsoft.EntityFrameworkCore.dll but was not handled in user code

Additional information: Index was outside the bounds of the array.

   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal.MaterializerFactory.CreateMaterializer(IEntityType entityType, SelectExpression selectExpression, Func`3 projectionAdder, IQuerySource querySource)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.RelationalEntityQueryableExpressionVisitor.CreateShaper(Type elementType, IEntityType entityType, SelectExpression selectExpression)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.RelationalEntityQueryableExpressionVisitor.VisitEntityQueryable(Type elementType)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.EntityQueryableExpressionVisitor.VisitConstant(ConstantExpression constantExpression)
   at System.Linq.Expressions.ConstantExpression.Accept(ExpressionVisitor visitor)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.ExpressionVisitorBase.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.ReplaceClauseReferences(Expression expression, IQuerySource querySource, Boolean inProjection)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CompileMainFromClauseExpression(MainFromClause mainFromClause, QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.CompileMainFromClauseExpression(MainFromClause mainFromClause, QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitMainFromClause(MainFromClause fromClause, QueryModel queryModel)
   at Remotion.Linq.Clauses.MainFromClause.Accept(IQueryModelVisitor visitor, QueryModel queryModel)
   at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.Internal.SqlServerQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateAsyncQueryExecutor[TResult](QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileAsyncQuery[TResult](QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass20_0`1.<CompileAsyncQuery>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddAsyncQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileAsyncQuery[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, Expression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, LambdaExpression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.SingleAsync[TSource](IQueryable`1 source, Expression`1 predicate, CancellationToken cancellationToken)
   at GrefQL.Tests.Query.StarWarsQuery.<>c__DisplayClass0_0.<.ctor>b__0(ResolveFieldContext context) in C:\Dev\GrefQL\test\GrefQL.Tests\Query.cs:line 58
   at GraphQL.DocumentExecuter.<ResolveField>d__8.MoveNext() in C:\Home\projects\graphql-dotnet\src\GraphQL\Execution\DocumentExecuter.cs:line 173

[rowanmiller]

We should catch that there are non concrete types in model validation