Compile-time options validation source generation
In the options pattern, various methods for validating options are presented. These methods include using data annotation attributes or employing a custom validator. Data annotation attributes are validated at run time and can incur performance costs. This article demonstrates how to utilize the options validation source generator to produce optimized validation code at compile time.
Automatic IValidateOptions implementation generation
The options pattern article illustrates how to implement the IValidateOptions<TOptions> interface for validating options. The options validation source generator can automatically create the IValidateOptions interface implementation by leveraging data annotation attributes on the options class.
The content that follows takes the annotation attributes example that's shown in Options pattern and converts it to use the options validation source generator.
Consider the following appsettings.json file:
{
"MyCustomSettingsSection": {
"SiteTitle": "Amazing docs from awesome people!",
"Scale": 10,
"VerbosityLevel": 32
}
}
The following class binds to the "MyCustomSettingsSection" configuration section and applies a couple of DataAnnotations rules:
using System.ComponentModel.DataAnnotations;
namespace ConsoleJson.Example;
public sealed class SettingsOptions
{
public const string ConfigurationSectionName = "MyCustomSettingsSection";
[Required]
[RegularExpression(@"^[a-zA-Z''-'\s]{1,40}$")]
public required string SiteTitle { get; set; }
[Required]
[Range(0, 1_000,
ErrorMessage = "Value for {0} must be between {1} and {2}.")]
public required int? Scale { get; set; }
[Required]
public required int? VerbosityLevel { get; set; }
}
In the preceding SettingsOptions class, the ConfigurationSectionName property contains the name of the configuration section to bind to. In this scenario, the options object provides the name of its configuration section. The following data annotation attributes are used:
- RequiredAttribute: Specifies that the property is required.
- RegularExpressionAttribute: Specifies that the property value must match the specified regular expression pattern.
- RangeAttribute: Specifies that the property value must be within a specified range.
Tip
In addition to the RequiredAttribute, the properties also use the required modifier. This helps to ensure that consumers of the options object don't forget to set the property value, although it doesn't relate to the validation source generation feature.
The following code exemplifies how to bind the configuration section to the options object and validate the data annotations:
using ConsoleJson.Example;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Options;
HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);
builder.Services
.AddOptions<SettingsOptions>()
.Bind(builder.Configuration.GetSection(SettingsOptions.ConfigurationSectionName));
builder.Services
.AddSingleton<IValidateOptions<SettingsOptions>, ValidateSettingsOptions>();
using IHost app = builder.Build();
var settingsOptions =
app.Services.GetRequiredService<IOptions<SettingsOptions>>().Value;
await app.RunAsync();
Tip
When AOT compilation is enabled by including <PublishAot>true</PublishAot> in the .csproj file, the code might generate warnings such as IL2025 and IL3050. To mitigate these warnings, it's recommended to use the configuration source generator. To enable the configuration source generator, add the property <EnableConfigurationBindingGenerator>true</EnableConfigurationBindingGenerator> to the project file.
By leveraging compile-time source generation for options validation, you can generate performance-optimized validation code and eliminate the need for reflection, resulting in smoother AOT-compatible app building. The following code demonstrates how to use the options validation source generator:
using Microsoft.Extensions.Options;
namespace ConsoleJson.Example;
[OptionsValidator]
public partial class ValidateSettingsOptions : IValidateOptions<SettingsOptions>
{
}
The presence of the OptionsValidatorAttribute on an empty partial class instructs the options validation source generator to create the IValidateOptions interface implementation that validates SettingsOptions. The code that's generated by the options validation source generator will resemble the following example:
// <auto-generated/>
#nullable enable
#pragma warning disable CS1591 // Compensate for https://github.com/dotnet/roslyn/issues/54103
namespace ConsoleJson.Example
{
partial class ValidateSettingsOptions
{
/// <summary>
/// Validates a specific named options instance (or all when <paramref name="name"/> is <see langword="null" />).
/// </summary>
/// <param name="name">The name of the options instance being validated.</param>
/// <param name="options">The options instance.</param>
/// <returns>Validation result.</returns>
[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Extensions.Options.SourceGeneration", "8.0.9.3103")]
[System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessage("Trimming", "IL2026:RequiresUnreferencedCode",
Justification = "The created ValidationContext object is used in a way that never call reflection")]
public global::Microsoft.Extensions.Options.ValidateOptionsResult Validate(string? name, global::ConsoleJson.Example.SettingsOptions options)
{
global::Microsoft.Extensions.Options.ValidateOptionsResultBuilder? builder = null;
var context = new global::System.ComponentModel.DataAnnotations.ValidationContext(options);
var validationResults = new global::System.Collections.Generic.List<global::System.ComponentModel.DataAnnotations.ValidationResult>();
var validationAttributes = new global::System.Collections.Generic.List<global::System.ComponentModel.DataAnnotations.ValidationAttribute>(2);
context.MemberName = "SiteTitle";
context.DisplayName = string.IsNullOrEmpty(name) ? "SettingsOptions.SiteTitle" : $"{name}.SiteTitle";
validationAttributes.Add(global::__OptionValidationStaticInstances.__Attributes.A1);
validationAttributes.Add(global::__OptionValidationStaticInstances.__Attributes.A2);
if (!global::System.ComponentModel.DataAnnotations.Validator.TryValidateValue(options.SiteTitle, context, validationResults, validationAttributes))
{
(builder ??= new()).AddResults(validationResults);
}
context.MemberName = "Scale";
context.DisplayName = string.IsNullOrEmpty(name) ? "SettingsOptions.Scale" : $"{name}.Scale";
validationResults.Clear();
validationAttributes.Clear();
validationAttributes.Add(global::__OptionValidationStaticInstances.__Attributes.A1);
validationAttributes.Add(global::__OptionValidationStaticInstances.__Attributes.A3);
if (!global::System.ComponentModel.DataAnnotations.Validator.TryValidateValue(options.Scale, context, validationResults, validationAttributes))
{
(builder ??= new()).AddResults(validationResults);
}
context.MemberName = "VerbosityLevel";
context.DisplayName = string.IsNullOrEmpty(name) ? "SettingsOptions.VerbosityLevel" : $"{name}.VerbosityLevel";
validationResults.Clear();
validationAttributes.Clear();
validationAttributes.Add(global::__OptionValidationStaticInstances.__Attributes.A1);
if (!global::System.ComponentModel.DataAnnotations.Validator.TryValidateValue(options.VerbosityLevel, context, validationResults, validationAttributes))
{
(builder ??= new()).AddResults(validationResults);
}
return builder is null ? global::Microsoft.Extensions.Options.ValidateOptionsResult.Success : builder.Build();
}
}
}
namespace __OptionValidationStaticInstances
{
[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Extensions.Options.SourceGeneration", "8.0.9.3103")]
file static class __Attributes
{
internal static readonly global::System.ComponentModel.DataAnnotations.RequiredAttribute A1 = new global::System.ComponentModel.DataAnnotations.RequiredAttribute();
internal static readonly global::System.ComponentModel.DataAnnotations.RegularExpressionAttribute A2 = new global::System.ComponentModel.DataAnnotations.RegularExpressionAttribute(
"^[a-zA-Z''-'\\s]{1,40}$");
internal static readonly __OptionValidationGeneratedAttributes.__SourceGen__RangeAttribute A3 = new __OptionValidationGeneratedAttributes.__SourceGen__RangeAttribute(
(int)0,
(int)1000)
{
ErrorMessage = "Value for {0} must be between {1} and {2}."
};
}
}
namespace __OptionValidationStaticInstances
{
[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Extensions.Options.SourceGeneration", "8.0.9.3103")]
file static class __Validators
{
}
}
namespace __OptionValidationGeneratedAttributes
{
[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Extensions.Options.SourceGeneration", "8.0.9.3103")]
[global::System.AttributeUsage(global::System.AttributeTargets.Property | global::System.AttributeTargets.Field | global::System.AttributeTargets.Parameter, AllowMultiple = false)]
file class __SourceGen__RangeAttribute : global::System.ComponentModel.DataAnnotations.ValidationAttribute
{
public __SourceGen__RangeAttribute(int minimum, int maximum) : base()
{
Minimum = minimum;
Maximum = maximum;
OperandType = typeof(int);
}
public __SourceGen__RangeAttribute(double minimum, double maximum) : base()
{
Minimum = minimum;
Maximum = maximum;
OperandType = typeof(double);
}
public __SourceGen__RangeAttribute(global::System.Type type, string minimum, string maximum) : base()
{
OperandType = type;
NeedToConvertMinMax = true;
Minimum = minimum;
Maximum = maximum;
}
public object Minimum { get; private set; }
public object Maximum { get; private set; }
public bool MinimumIsExclusive { get; set; }
public bool MaximumIsExclusive { get; set; }
public global::System.Type OperandType { get; }
public bool ParseLimitsInInvariantCulture { get; set; }
public bool ConvertValueInInvariantCulture { get; set; }
public override string FormatErrorMessage(string name) =>
string.Format(global::System.Globalization.CultureInfo.CurrentCulture, GetValidationErrorMessage(), name, Minimum, Maximum);
private bool NeedToConvertMinMax { get; }
private bool Initialized { get; set; }
public override bool IsValid(object? value)
{
if (!Initialized)
{
if (Minimum is null || Maximum is null)
{
throw new global::System.InvalidOperationException("The minimum and maximum values must be set to valid values.");
}
if (NeedToConvertMinMax)
{
System.Globalization.CultureInfo culture = ParseLimitsInInvariantCulture ? global::System.Globalization.CultureInfo.InvariantCulture : global::System.Globalization.CultureInfo.CurrentCulture;
Minimum = ConvertValue(Minimum, culture) ?? throw new global::System.InvalidOperationException("The minimum and maximum values must be set to valid values.");
Maximum = ConvertValue(Maximum, culture) ?? throw new global::System.InvalidOperationException("The minimum and maximum values must be set to valid values.");
}
int cmp = ((global::System.IComparable)Minimum).CompareTo((global::System.IComparable)Maximum);
if (cmp > 0)
{
throw new global::System.InvalidOperationException("The maximum value '{Maximum}' must be greater than or equal to the minimum value '{Minimum}'.");
}
else if (cmp == 0 && (MinimumIsExclusive || MaximumIsExclusive))
{
throw new global::System.InvalidOperationException("Cannot use exclusive bounds when the maximum value is equal to the minimum value.");
}
Initialized = true;
}
if (value is null or string { Length: 0 })
{
return true;
}
System.Globalization.CultureInfo formatProvider = ConvertValueInInvariantCulture ? global::System.Globalization.CultureInfo.InvariantCulture : global::System.Globalization.CultureInfo.CurrentCulture;
object? convertedValue;
try
{
convertedValue = ConvertValue(value, formatProvider);
}
catch (global::System.Exception e) when (e is global::System.FormatException or global::System.InvalidCastException or global::System.NotSupportedException)
{
return false;
}
var min = (global::System.IComparable)Minimum;
var max = (global::System.IComparable)Maximum;
return
(MinimumIsExclusive ? min.CompareTo(convertedValue) < 0 : min.CompareTo(convertedValue) <= 0) &&
(MaximumIsExclusive ? max.CompareTo(convertedValue) > 0 : max.CompareTo(convertedValue) >= 0);
}
private string GetValidationErrorMessage()
{
return (MinimumIsExclusive, MaximumIsExclusive) switch
{
(false, false) => "The field {0} must be between {1} and {2}.",
(true, false) => "The field {0} must be between {1} exclusive and {2}.",
(false, true) => "The field {0} must be between {1} and {2} exclusive.",
(true, true) => "The field {0} must be between {1} exclusive and {2} exclusive.",
};
}
private object? ConvertValue(object? value, System.Globalization.CultureInfo formatProvider)
{
if (value is string stringValue)
{
value = global::System.Convert.ChangeType(stringValue, OperandType, formatProvider);
}
else
{
value = global::System.Convert.ChangeType(value, OperandType, formatProvider);
}
return value;
}
}
}
The generated code is optimized for performance and doesn't rely on reflection. It's also AOT-compatible. The generated code is placed in a file named Validators.g.cs.
Note
You don't need to take any additional steps to enable the options validation source generator. It's automatically enabled by default when your project references Microsoft.Extensions.Options version 8 or later, or when building an ASP.NET application.
The only step you need to take is to add the following to the startup code:
builder.Services
.AddSingleton<IValidateOptions<SettingsOptions>, ValidateSettingsOptions>();
Note
Calling OptionsBuilderDataAnnotationsExtensions.ValidateDataAnnotations<TOptions>(OptionsBuilder<TOptions>) isn't required when using the options validation source generator.
When the application attempts to access the options object, the generated code for options validation is executed to validate the options object. The following code snippet illustrates how to access the options object:
var settingsOptions =
app.Services.GetRequiredService<IOptions<SettingsOptions>>().Value;
Replaced data annotation attributes
Upon close examination of the generated code, you'll observe that the original data annotation attributes, such as RangeAttribute, that were initially applied to the property SettingsOptions.Scale, have been substituted with custom attributes like __SourceGen__RangeAttribute. This substitution is made because the RangeAttribute relies on reflection for validation. In contrast, __SourceGen__RangeAttribute is a custom attribute optimized for performance and doesn't depend on reflection, making the code AOT-compatible. The same pattern of attribute replacement will be applied on MaxLengthAttribute, MinLengthAttribute, and LengthAttribute in addition to RangeAttribute.
For anyone developing custom data annotation attributes, it's advisable to refrain from using reflection for validation. Instead, it's recommended to craft strongly typed code that doesn't rely on reflection. This approach ensures smooth compatibility with AOT builds.
