TRLS021 — HasIndex references a Maybe property

• Severity: Warning
• Category: Trellis

What it detects

Flags EntityTypeBuilder.HasIndex(...) lambda expressions that reference a Maybe<T> property when Trellis.EntityFrameworkCore's Maybe convention is active.

Why it matters

EF Core indexes the generated storage member, not the Maybe<T> CLR property. A normal HasIndex call can silently fail to create the index you thought you configured.

Warning

The diagnostic tells you both the Maybe<T> property name and the generated storage-member fallback name so you can see what EF Core actually maps.

Bad example

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;
using Trellis;

sealed class OrderConfiguration : IEntityTypeConfiguration<Order>
{
    public void Configure(EntityTypeBuilder<Order> builder)
    {
        builder.HasIndex(order => order.SubmittedAt);
    }
}

sealed class Order
{
    public string Status { get; set; } = string.Empty;
    public Maybe<DateTime> SubmittedAt { get; set; }
}

Good example

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;
using Trellis;
using Trellis.EntityFrameworkCore;

sealed class OrderConfiguration : IEntityTypeConfiguration<Order>
{
    public void Configure(EntityTypeBuilder<Order> builder)
    {
        builder.HasTrellisIndex(order => new { order.Status, order.SubmittedAt });
    }
}

sealed class Order
{
    public string Status { get; set; } = string.Empty;
    public Maybe<DateTime> SubmittedAt { get; set; }
}

Code fix available

No.

Configuration

Use standard Roslyn configuration if you need to suppress this rule in a specific scope.

dotnet_diagnostic.TRLS021.severity = none

#pragma warning disable TRLS021
// Intentional: documented exception or test-only pattern.
#pragma warning restore TRLS021

Tip

Prefer HasTrellisIndex(...) for mixed regular and Maybe<T> properties. Use string-based HasIndex(...) only when you need the storage member directly.