Dotnet Source Gen Options Validation

Convert options validation to use the compile-time source generator, enabling AOT-compatible, reflection-free validation at startup.

When to Use

• Preparing application for Native AOT compilation
• Eliminating reflection-based validation overhead
• Ensuring validation errors surface at compile time rather than runtime
• Migrating from ValidateDataAnnotations() to source-generated validation

Steps

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

2. Check existing validation setup:

   • If class already has a corresponding [OptionsValidator] partial class, skip it
   • Note any existing ValidateDataAnnotations() calls for removal later

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

   [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

4. Register the validator in DI:

   services.AddSingleton<IValidateOptions<MyOptions>, ValidateMyOptions>();
   

   • Replace any existing ValidateDataAnnotations() calls
   • Ensure Microsoft.Extensions.Options using directive is present

5. Verify with build:

   dotnet build
   

6. If build fails, check for:

   • Missing partial keyword on validator class
   • Unsupported validation attributes
   • Missing package reference to Microsoft.Extensions.Options

7. Report results:

   • List all validator classes created
   • List all DI registrations added
   • Confirm build status

Supported Validation Attributes

• [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

Notes

• 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