Add operation transformer for query parameter validation (Issue #200)

CHANGELOG.md

@@ -1,3 +1,13 @@
+# Changes in 7.1.4-beta
+- Added: `FluentValidationOperationTransformer` (`IOpenApiOperationTransformer`) for `MicroElements.AspNetCore.OpenApi.FluentValidation` (Issue #200)
+  - Query parameters with `[AsParameters]` now receive validation constraints (min/max, required, pattern, etc.)
+  - Supports container type resolution with fallback via reflection for `[AsParameters]`
+  - Copies validation constraints from schema properties to parameter schemas
+  - Registered automatically via `AddFluentValidationRules()`
+- Fixed: Nested DTOs in request body not receiving validation constraints (Issue #200)
+  - `FluentValidationSchemaTransformer` skipped all property-level schemas, but for nested object types this was the only transformer call
+  - Now processes property-level schemas for complex types using the property type's validator
+
 # Changes in 7.1.3
 - Fixed: `$ref` replaced with inline schema copy when using `SetValidator` with nested object types (Issue #198)
   - `ResolveRefProperty` (introduced in 7.1.2 for BigInteger isolation) replaced all `$ref` properties with copies, destroying reference structure in the OpenAPI document

src/MicroElements.AspNetCore.OpenApi.FluentValidation/AspNetCore/OpenApiOptionsExtensions.cs

@@ -19,6 +19,7 @@ public static class OpenApiOptionsExtensions
         public static OpenApiOptions AddFluentValidationRules(this OpenApiOptions options)
         {
             options.AddSchemaTransformer<FluentValidationSchemaTransformer>();
+            options.AddOperationTransformer<FluentValidationOperationTransformer>();
             return options;
         }
     }

src/MicroElements.AspNetCore.OpenApi.FluentValidation/AspNetCore/ServiceCollectionExtensions.cs

@@ -36,6 +36,7 @@ public static IServiceCollection AddFluentValidationRulesToOpenApi(
             // Transient (not Scoped) because .NET 10 build-time document generation
             // runs without an HTTP scope, causing scoped resolution to fail.
             services.TryAddTransient<FluentValidationSchemaTransformer>();
+            services.TryAddTransient<FluentValidationOperationTransformer>();
 
             // Register JsonSerializerOptions (reference to Microsoft.AspNetCore.Mvc.JsonOptions.Value)
             services.TryAddTransient<AspNetJsonSerializerOptions>(provider => new AspNetJsonSerializerOptions(provider.GetJsonSerializerOptionsOrDefault()));

src/MicroElements.AspNetCore.OpenApi.FluentValidation/FluentValidationOperationTransformer.cs

@@ -0,0 +1,351 @@
+// Copyright (c) MicroElements. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Threading;
+using System.Threading.Tasks;
+using FluentValidation;
+using MicroElements.OpenApi;
+using MicroElements.OpenApi.Core;
+using MicroElements.OpenApi.FluentValidation;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.OpenApi;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+#if OPENAPI_V2
+using Microsoft.OpenApi;
+#else
+using Microsoft.OpenApi.Models;
+#endif
+
+namespace MicroElements.AspNetCore.OpenApi.FluentValidation
+{
+    /// <summary>
+    /// <see cref="IOpenApiOperationTransformer"/> that applies FluentValidation rules
+    /// to query, route, and header parameters generated by Microsoft.AspNetCore.OpenApi.
+    /// Issue #200: Query parameters with [AsParameters] were not getting validation constraints.
+    /// </summary>
+    public class FluentValidationOperationTransformer : IOpenApiOperationTransformer
+    {
+        private readonly ILogger _logger;
+        private readonly IValidatorRegistry _validatorRegistry;
+        private readonly IReadOnlyList<IFluentValidationRule<OpenApiSchema>> _rules;
+        private readonly SchemaGenerationOptions _schemaGenerationOptions;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="FluentValidationOperationTransformer"/> class.
+        /// </summary>
+        public FluentValidationOperationTransformer(
+            ILoggerFactory? loggerFactory = null,
+            IValidatorRegistry? validatorRegistry = null,
+            IFluentValidationRuleProvider<OpenApiSchema>? fluentValidationRuleProvider = null,
+            IEnumerable<FluentValidationRule>? rules = null,
+            IOptions<SchemaGenerationOptions>? schemaGenerationOptions = null)
+        {
+            _logger = loggerFactory?.CreateLogger(typeof(FluentValidationOperationTransformer)) ?? NullLogger.Instance;
+            _validatorRegistry = validatorRegistry ?? throw new ArgumentNullException(nameof(validatorRegistry));
+
+            fluentValidationRuleProvider ??= new DefaultFluentValidationRuleProvider(schemaGenerationOptions);
+            _rules = fluentValidationRuleProvider.GetRules().ToArray().OverrideRules(rules);
+            _schemaGenerationOptions = schemaGenerationOptions?.Value ?? new SchemaGenerationOptions();
+
+            _logger.LogDebug("FluentValidationOperationTransformer Created");
+        }
+
+        /// <inheritdoc />
+        public Task TransformAsync(
+            OpenApiOperation operation,
+            OpenApiOperationTransformerContext context,
+            CancellationToken cancellationToken)
+        {
+            try
+            {
+                if (operation.Parameters != null && operation.Parameters.Count > 0)
+                {
+                    ApplyRulesToParameters(operation, context);
+                }
+            }
+            catch (Exception e)
+            {
+                _logger.LogWarning(0, e, "Error applying FluentValidation rules to operation parameters");
+            }
+
+            return Task.CompletedTask;
+        }
+
+        private void ApplyRulesToParameters(OpenApiOperation operation, OpenApiOperationTransformerContext context)
+        {
+            // Group parameters by container type to avoid redundant validator lookups and schema builds.
+            var parameterGroups = new Dictionary<Type, (IValidator Validator, OpenApiSchema Schema)>();
+
+            foreach (var operationParameter in operation.Parameters)
+            {
+                var apiParameterDescription = context.Description.ParameterDescriptions
+                    .FirstOrDefault(d => d.Name.Equals(operationParameter.Name, StringComparison.InvariantCultureIgnoreCase));
+
+                var modelMetadata = apiParameterDescription?.ModelMetadata;
+                if (modelMetadata == null)
+                    continue;
+
+                var parameterType = modelMetadata.ContainerType;
+
+                // Fallback: resolve container type from [AsParameters] attribute
+                if (parameterType == null)
+                {
+                    var methodInfo = GetMethodInfo(context.Description);
+                    parameterType = ResolveContainerType(operationParameter.Name, methodInfo);
+                }
+
+                if (parameterType == null)
+                    continue;
+
+                // Reuse validator and schema for the same container type
+                if (!parameterGroups.TryGetValue(parameterType, out var cached))
+                {
+                    var validator = _validatorRegistry.GetValidator(parameterType);
+                    if (validator == null)
+                        continue;
+
+                    var schema = BuildSchemaForType(parameterType);
+                    if (schema.Properties == null || schema.Properties.Count == 0)
+                        continue;
+
+                    cached = (validator, schema);
+                    parameterGroups[parameterType] = cached;
+                }
+
+                ApplyRulesToParameter(operationParameter, parameterType, cached.Validator, cached.Schema);
+            }
+        }
+
+        private void ApplyRulesToParameter(
+#if OPENAPI_V2
+            IOpenApiParameter operationParameter,
+#else
+            OpenApiParameter operationParameter,
+#endif
+            Type parameterType,
+            IValidator validator,
+            OpenApiSchema schema)
+        {
+            var schemaPropertyName = operationParameter.Name;
+
+            // For nested [FromQuery] parameters (e.g., "operation.op"), use only the leaf name
+            var dotIndex = schemaPropertyName.LastIndexOf('.');
+            if (dotIndex >= 0)
+                schemaPropertyName = schemaPropertyName.Substring(dotIndex + 1);
+
+            // Find matching property in schema
+            var apiProperty = OpenApiSchemaCompatibility.GetProperties(schema)
+                .FirstOrDefault(property => property.Key.EqualsIgnoreAll(schemaPropertyName));
+            if (apiProperty.Key != null)
+            {
+                schemaPropertyName = apiProperty.Key;
+            }
+            else
+            {
+                var propertyInfo = parameterType.GetProperty(schemaPropertyName);
+                if (propertyInfo != null && _schemaGenerationOptions.NameResolver != null)
+                {
+                    schemaPropertyName = _schemaGenerationOptions.NameResolver.GetPropertyName(propertyInfo);
+                }
+            }
+
+            var schemaProvider = new AspNetCoreSchemaProvider(null, _logger);
+            var schemaContext = new AspNetCoreSchemaGenerationContext(
+                schema: schema,
+                schemaType: parameterType,
+                rules: _rules,
+                schemaGenerationOptions: _schemaGenerationOptions,
+                schemaProvider: schemaProvider);
+
+            FluentValidationSchemaBuilder.ApplyRulesToSchema(
+                schemaType: parameterType,
+                schemaPropertyNames: new[] { schemaPropertyName },
+                validator: validator,
+                logger: _logger,
+                schemaGenerationContext: schemaContext);
+
+            // Copy required flag
+            if (OpenApiSchemaCompatibility.RequiredContains(schema, schemaPropertyName))
+            {
+#if OPENAPI_V2
+                if (operationParameter is OpenApiParameter openApiParameter)
+                    openApiParameter.Required = true;
+#else
+                operationParameter.Required = true;
+#endif
+            }
+
+            // Copy validation constraints from schema property to parameter schema
+#if OPENAPI_V2
+            var parameterSchema = operationParameter.Schema as OpenApiSchema;
+#else
+            var parameterSchema = operationParameter.Schema;
+#endif
+            if (parameterSchema != null)
+            {
+                if (OpenApiSchemaCompatibility.TryGetProperty(schema, schemaPropertyName, out var property))
+                {
+                    if (property != null)
+                    {
+                        CopyValidationProperties(property, parameterSchema);
+                    }
+                }
+            }
+        }
+
+        /// <summary>
+        /// Builds a temporary OpenApiSchema for a type by reflecting its properties.
+        /// </summary>
+        private OpenApiSchema BuildSchemaForType(Type type)
+        {
+            var schema = new OpenApiSchema();
+#if OPENAPI_V2
+            var properties = new Dictionary<string, IOpenApiSchema>();
+#else
+            var properties = new Dictionary<string, OpenApiSchema>();
+#endif
+
+            foreach (var prop in type.GetProperties(BindingFlags.Public | BindingFlags.Instance))
+            {
+                var propName = prop.Name;
+                if (_schemaGenerationOptions.NameResolver != null)
+                    propName = _schemaGenerationOptions.NameResolver.GetPropertyName(prop);
+
+                var propSchema = new OpenApiSchema();
+                SetSchemaType(propSchema, prop.PropertyType);
+                properties[propName] = propSchema;
+            }
+
+            schema.Properties = properties;
+            return schema;
+        }
+
+        /// <summary>
+        /// Sets basic type information on a schema from a CLR type.
+        /// TODO: Add support for DateTime, DateTimeOffset, Guid, enum types, and collections.
+        /// Currently these all fall through to "string" which may cause incorrect schema types.
+        /// </summary>
+        private static void SetSchemaType(OpenApiSchema schema, Type type)
+        {
+            var underlyingType = Nullable.GetUnderlyingType(type) ?? type;
+
+#if OPENAPI_V2
+            if (underlyingType == typeof(int) || underlyingType == typeof(long) || underlyingType == typeof(short) || underlyingType == typeof(byte))
+                schema.Type = JsonSchemaType.Integer;
+            else if (underlyingType == typeof(float) || underlyingType == typeof(double) || underlyingType == typeof(decimal))
+                schema.Type = JsonSchemaType.Number;
+            else if (underlyingType == typeof(string))
+                schema.Type = JsonSchemaType.String;
+            else if (underlyingType == typeof(bool))
+                schema.Type = JsonSchemaType.Boolean;
+            else
+                schema.Type = JsonSchemaType.String;
+#else
+            if (underlyingType == typeof(int) || underlyingType == typeof(long) || underlyingType == typeof(short) || underlyingType == typeof(byte))
+                schema.Type = "integer";
+            else if (underlyingType == typeof(float) || underlyingType == typeof(double) || underlyingType == typeof(decimal))
+                schema.Type = "number";
+            else if (underlyingType == typeof(string))
+                schema.Type = "string";
+            else if (underlyingType == typeof(bool))
+                schema.Type = "boolean";
+            else
+                schema.Type = "string";
+#endif
+        }
+
+        /// <summary>
+        /// Copies validation-related properties from source schema to target schema.
+        /// </summary>
+        private static void CopyValidationProperties(OpenApiSchema source, OpenApiSchema target)
+        {
+            if (source.MinLength != null) target.MinLength = source.MinLength;
+            if (source.MaxLength != null) target.MaxLength = source.MaxLength;
+            if (source.MinItems != null) target.MinItems = source.MinItems;
+            if (source.MaxItems != null) target.MaxItems = source.MaxItems;
+            if (source.Pattern != null) target.Pattern = source.Pattern;
+            if (source.Minimum != null) target.Minimum = source.Minimum;
+            if (source.Maximum != null) target.Maximum = source.Maximum;
+            if (source.ExclusiveMinimum != null) target.ExclusiveMinimum = source.ExclusiveMinimum;
+            if (source.ExclusiveMaximum != null) target.ExclusiveMaximum = source.ExclusiveMaximum;
+            if (source.Format != null) target.Format = source.Format;
+        }
+
+        /// <summary>
+        /// Resolves the container type for a parameter by inspecting [AsParameters] on method parameters.
+        /// For nested paths (e.g., "Filter.MinAge"), walks the path to find the correct container type.
+        /// </summary>
+        private static Type? ResolveContainerType(string parameterName, MethodInfo? methodInfo)
+        {
+            if (methodInfo == null)
+                return null;
+
+            // Split dot-path into segments (e.g., "Filter.MinAge" => ["Filter", "MinAge"])
+            var segments = parameterName.Split('.');
+
+            foreach (var param in methodInfo.GetParameters())
+            {
+                if (param.GetCustomAttribute<AsParametersAttribute>() == null)
+                    continue;
+
+                var paramType = param.ParameterType;
+
+                if (segments.Length == 1)
+                {
+                    // Simple case: direct property on [AsParameters] type
+                    var property = paramType.GetProperties()
+                        .FirstOrDefault(p => p.Name.Equals(segments[0], StringComparison.OrdinalIgnoreCase));
+                    if (property != null)
+                        return paramType;
+                }
+                else
+                {
+                    // Nested case: walk path segments to find the container of the leaf property.
+                    // Note: ASP.NET Core minimal APIs do not currently emit dot-path parameters
+                    // for nested [AsParameters] types. This branch is defensive code for potential
+                    // future framework support or MVC controller scenarios.
+                    // e.g., "Filter.MinAge" => find Filter on paramType, return Filter's type
+                    var currentType = paramType;
+                    for (int i = 0; i < segments.Length - 1; i++)
+                    {
+                        var navProp = currentType.GetProperties()
+                            .FirstOrDefault(p => p.Name.Equals(segments[i], StringComparison.OrdinalIgnoreCase));
+                        if (navProp == null)
+                        {
+                            currentType = null;
+                            break;
+                        }
+
+                        currentType = navProp.PropertyType;
+                    }
+
+                    if (currentType != null)
+                    {
+                        var leafProp = currentType.GetProperties()
+                            .FirstOrDefault(p => p.Name.Equals(segments[^1], StringComparison.OrdinalIgnoreCase));
+                        if (leafProp != null)
+                            return currentType;
+                    }
+                }
+            }
+
+            return null;
+        }
+
+        /// <summary>
+        /// Extracts MethodInfo from an ApiDescription.
+        /// </summary>
+        private static MethodInfo? GetMethodInfo(Microsoft.AspNetCore.Mvc.ApiExplorer.ApiDescription apiDescription)
+        {
+            return apiDescription.ActionDescriptor?.EndpointMetadata?
+                .OfType<MethodInfo>()
+                .FirstOrDefault();
+        }
+    }
+}