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
• •Source generation happens at compile time; value validation runs at startup
• •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:

   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
4. •

   Register the validator in DI:

   csharp

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

   • •Replace any existing ValidateDataAnnotations() calls
   • •Ensure Microsoft.Extensions.Options using directive is present
5. •

   Verify with build:

   bash

   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