dotnet-source-gen-options-validation

• Preparing application for Native AOT compilation
• Eliminating reflection-based validation overhead
• Source generation happens at compile time; value validation runs at startup
• Migrating from ValidateDataAnnotations() to source-generated validation

1. Find options classes with data annotations:

- Search for classes using [Required], [Range], [RegularExpression], [MaxLength], [MinLength], [Length]

- These are typically in files matching Options.cs or Settings.cs

1. Check existing validation setup:

- If class already has a corresponding [OptionsValidator] partial class, skip it

- Note any existing ValidateDataAnnotations() calls for removal later

1. For each options class, create a partial validator class:

```csharp

[OptionsValidator]

public partial class Validate{OptionsClassName} : IValidateOptions<{OptionsClassName}>

{

}

```

- Place the validator in the same namespace as the options class

- The source generator will implement the validation logic at compile time

1. Register the validator in DI:

```csharp

services.AddSingleton, ValidateMyOptions>();

```

- Replace any existing ValidateDataAnnotations() calls

- Ensure Microsoft.Extensions.Options using directive is present

1. Verify with build:

```bash

dotnet build

```

1. If build fails, check for:

- Missing partial keyword on validator class

- Unsupported validation attributes

- Missing package reference to Microsoft.Extensions.Options

1. Report results:

- List all validator classes created

- List all DI registrations added

- Confirm build status

• [Required] - Property must have a value
• [Range] - Numeric value within specified range
• [RegularExpression] - String matches regex pattern
• [MaxLength] - Maximum length for strings/collections
• [MinLength] - Minimum length for strings/collections
• [Length] - Exact or range length constraint

• Requires .NET 8.0 or higher
• Requires Microsoft.Extensions.Options version 8.0 or higher
• ValidateDataAnnotations() is NOT needed and should be removed
• The [OptionsValidator] attribute triggers source generation
• Validation runs at startup when options are first resolved
• Unsupported attributes will produce compiler warnings