dotnet-source-gen-options-validation

Development

Converts options validation to use the compile-time source generator. Use when the user wants AOT-compatible, reflection-free options validation.

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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

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
Check existing validation setup:
- If class already has a corresponding [OptionsValidator] partial class, skip it
- Note any existing ValidateDataAnnotations() calls for removal later
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
Register the validator in DI:
```
services.AddSingleton<IValidateOptions<MyOptions>, ValidateMyOptions>();
```
- Replace any existing ValidateDataAnnotations() calls
- Ensure Microsoft.Extensions.Options using directive is present
Verify with build:
```
dotnet build
```
If build fails, check for:
- Missing partial keyword on validator class
- Unsupported validation attributes
- Missing package reference to Microsoft.Extensions.Options
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