SQL Server: Math.Sign(decimal) throws InvalidCastException - SIGN returns decimal, expected Int32

[RyanLamansky]

Bug description

Math.Sign(decimal) in a SQL Server query throws InvalidCastException at materialization time. The translator emits a bare SIGN(<col>), but per the T-SQL SIGN documentation SIGN returns the same data type as its input. For a decimal column it returns decimal, not int. EF Core's materializer reads the column with SqlDataReader.GetInt32 (matching the C# return type of Math.Sign(decimal), which is int), and that throws.

Your code

using Microsoft.EntityFrameworkCore;

using var db = new ReproContext();
db.Database.EnsureDeleted();
db.Database.EnsureCreated();

db.Samples.Add(new Sample { Value = 1m });
db.SaveChanges();

_ = db.Samples.Select(s => Math.Sign(s.Value)).ToList();

class Sample
{
    public int Id { get; set; }
    public decimal Value { get; set; }
}

class ReproContext : DbContext
{
    public DbSet<Sample> Samples => Set<Sample>();

    protected override void OnConfiguring(DbContextOptionsBuilder options)
        => options.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=EfCore10SignRepro");
}

Stack traces

System.InvalidCastException: Unable to cast object of type 'System.Decimal' to type 'System.Int32'.
   at Microsoft.Data.SqlClient.SqlBuffer.get_Int32()
   at Microsoft.Data.SqlClient.SqlDataReader.GetInt32(Int32 i)
   at lambda_method...(Closure, QueryContext, DbDataReader, ResultContext, SingleQueryResultCoordinator)
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.Enumerator.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

Verbose output

EF Core version

10.0.7

Database provider

Microsoft.EntityFrameworkCore.SqlServer

Target framework

.NET 10

Operating system

Linux

IDE

None

[roji]

AI Triage

The below is an AI-generated analysis and may contain inaccuracies.

Issue type: Bug
Area labels: area-query, area-sqlserver

Analysis

The bug is confirmed by code analysis. In SqlServerMathTranslator.cs, Math.Sign(decimal) is translated to SIGN(col) with method.ReturnType (typeof(int)) as the expected CLR return type. However, T-SQL's SIGN function returns the same data type as its input — for a decimal column, it returns decimal, not int. The materializer therefore calls SqlDataReader.GetInt32() on a decimal value, causing the InvalidCastException.

The same issue likely also affects double and float inputs in projection scenarios (not just Where clauses), since SIGN(float) returns float in T-SQL but Math.Sign(double) returns int in C#. The existing tests only use Math.Sign inside Where clauses (comparing to int), which avoids the materialization path.

Regression: No — the Math.Sign(decimal) translation was added in EF Core 2.0 (commit 11dd5f60), and the type mismatch has been present since then. No existing tests cover Math.Sign in a projection (only in Where filters).

Duplicates: None found.

Minimal repro

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

await using var context = new TestContext();
await context.Database.EnsureDeletedAsync();
await context.Database.EnsureCreatedAsync();

context.Samples.Add(new Sample { Value = 1m });
await context.SaveChangesAsync();

var results = await context.Samples.Select(s => Math.Sign(s.Value)).ToListAsync();
Console.WriteLine($"Result: {results[0]}");

public class Sample
{
    public int Id { get; set; }
    public decimal Value { get; set; }
}

public class TestContext : DbContext
{
    public DbSet<Sample> Samples { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer(Environment.GetEnvironmentVariable("Test__SqlServer__DefaultConnection"))
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();
}

Expected: Prints Result: 1
Actual: Throws System.InvalidCastException: Unable to cast object of type 'System.Decimal' to type 'System.Int32'.