Map [MinLength]/[MaxLength] on dictionary properties to minProperties / maxProperties

src/Swashbuckle.AspNetCore.SwaggerGen/SchemaGenerator/OpenApiSchemaExtensions.cs

@@ -185,6 +185,10 @@ private static void ApplyMinLengthAttribute(OpenApiSchema schema, MinLengthAttri
         {
             schema.MinItems = minLengthAttribute.Length;
         }
+        else if (schema.Type is { } objectType && objectType.HasFlag(JsonSchemaTypes.Object))
+        {
+            schema.MinProperties = minLengthAttribute.Length;
+        }
         else
         {
             schema.MinLength = minLengthAttribute.Length;
@@ -209,6 +213,10 @@ private static void ApplyMaxLengthAttribute(OpenApiSchema schema, MaxLengthAttri
         {
             schema.MaxItems = maxLengthAttribute.Length;
         }
+        else if (schema.Type is { } objectType && objectType.HasFlag(JsonSchemaTypes.Object))
+        {
+            schema.MaxProperties = maxLengthAttribute.Length;
+        }
         else
         {
             schema.MaxLength = maxLengthAttribute.Length;
@@ -234,6 +242,11 @@ private static void ApplyLengthAttribute(OpenApiSchema schema, LengthAttribute l
             schema.MinItems = lengthAttribute.MinimumLength;
             schema.MaxItems = lengthAttribute.MaximumLength;
         }
+        else if (schema.Type is { } objectType && objectType.HasFlag(JsonSchemaTypes.Object))
+        {
+            schema.MinProperties = lengthAttribute.MinimumLength;
+            schema.MaxProperties = lengthAttribute.MaximumLength;
+        }
         else
         {
             schema.MinLength = lengthAttribute.MinimumLength;

test/Swashbuckle.AspNetCore.Newtonsoft.Test/SchemaGenerator/NewtonsoftSchemaGeneratorTests.cs

@@ -373,10 +373,16 @@ public void GenerateSchema_SetsValidationProperties_IfComplexTypeHasValidationAt
         Assert.Equal(3, schema.Properties["StringWithMinMaxLength"].MaxLength);
         Assert.Equal(1, schema.Properties["ArrayWithMinMaxLength"].MinItems);
         Assert.Equal(3, schema.Properties["ArrayWithMinMaxLength"].MaxItems);
+        Assert.Equal(1, schema.Properties["IReadOnlyDictionaryWithMinMaxLength"].MinProperties);
+        Assert.Equal(3, schema.Properties["IReadOnlyDictionaryWithMinMaxLength"].MaxProperties);
+        Assert.Null(schema.Properties["IReadOnlyDictionaryWithMinMaxLength"].MinLength);
+        Assert.Null(schema.Properties["IReadOnlyDictionaryWithMinMaxLength"].MaxLength);
         Assert.Equal(1, schema.Properties["StringWithLength"].MinLength);
         Assert.Equal(3, schema.Properties["StringWithLength"].MaxLength);
         Assert.Equal(1, schema.Properties["ArrayWithLength"].MinItems);
         Assert.Equal(3, schema.Properties["ArrayWithLength"].MaxItems);
+        Assert.Equal(1, schema.Properties["DictionaryWithLengthAttribute"].MinProperties);
+        Assert.Equal(3, schema.Properties["DictionaryWithLengthAttribute"].MaxProperties);
         Assert.NotNull(schema.Properties["IntWithExclusiveRange"].ExclusiveMinimum);
         Assert.NotNull(schema.Properties["IntWithExclusiveRange"].ExclusiveMaximum);
         Assert.Equal("byte", schema.Properties["StringWithBase64"].Format);

test/Swashbuckle.AspNetCore.SwaggerGen.Test/SchemaGenerator/JsonSerializerSchemaGeneratorTests.cs

@@ -373,10 +373,16 @@ public void GenerateSchema_SetsValidationProperties_IfComplexTypeHasValidationAt
         Assert.Equal(3, schema.Properties["StringWithMinMaxLength"].MaxLength);
         Assert.Equal(1, schema.Properties["ArrayWithMinMaxLength"].MinItems);
         Assert.Equal(3, schema.Properties["ArrayWithMinMaxLength"].MaxItems);
+        Assert.Equal(1, schema.Properties["IReadOnlyDictionaryWithMinMaxLength"].MinProperties);
+        Assert.Equal(3, schema.Properties["IReadOnlyDictionaryWithMinMaxLength"].MaxProperties);
+        Assert.Null(schema.Properties["IReadOnlyDictionaryWithMinMaxLength"].MinLength);
+        Assert.Null(schema.Properties["IReadOnlyDictionaryWithMinMaxLength"].MaxLength);
         Assert.Equal(1, schema.Properties["StringWithLength"].MinLength);
         Assert.Equal(3, schema.Properties["StringWithLength"].MaxLength);
         Assert.Equal(1, schema.Properties["ArrayWithLength"].MinItems);
         Assert.Equal(3, schema.Properties["ArrayWithLength"].MaxItems);
+        Assert.Equal(1, schema.Properties["DictionaryWithLengthAttribute"].MinProperties);
+        Assert.Equal(3, schema.Properties["DictionaryWithLengthAttribute"].MaxProperties);
         Assert.NotNull(schema.Properties["IntWithExclusiveRange"].ExclusiveMinimum);
         Assert.NotNull(schema.Properties["IntWithExclusiveRange"].ExclusiveMaximum);
         Assert.Equal("byte", schema.Properties["StringWithBase64"].Format);
@@ -397,6 +403,33 @@ public void GenerateSchema_SetsValidationProperties_IfComplexTypeHasValidationAt
         Assert.True(schema.Properties[nameof(TypeWithValidationAttributes.StringWithReadOnly)].ReadOnly);
     }
 
+    [Theory]
+    [InlineData(typeof(TypeWithValidationAttributes))]
+    [InlineData(typeof(TypeWithValidationAttributesViaMetadataType))]
+    public void GenerateSchema_DictionaryWithLengthAttributes_OpenApiJsonUsesMinAndMaxProperties(Type type)
+    {
+        // Arrange
+        var schemaRepository = new SchemaRepository();
+        Subject().GenerateSchema(type, schemaRepository);
+
+        var document = new OpenApiDocument
+        {
+            Components = new OpenApiComponents { Schemas = schemaRepository.Schemas },
+        };
+
+        // Act - serialize to OpenAPI 3.0 JSON, the same writer used by the runtime
+        using var writer = new StringWriter();
+        var jsonWriter = new OpenApiJsonWriter(writer);
+        document.SerializeAsV3(jsonWriter);
+        var json = writer.ToString();
+
+        // Assert - the dictionary constraints surface as minProperties/maxProperties
+        // in the generated OpenAPI document. Before the fix these would have been
+        // emitted as minLength/maxLength on an object schema, which is invalid per spec.
+        Assert.Contains("\"minProperties\": 1", json);
+        Assert.Contains("\"maxProperties\": 3", json);
+    }
+
     [Fact]
     public void GenerateSchema_SetsReadOnlyAndWriteOnlyFlags_IfPropertyIsRestricted()
     {

test/Swashbuckle.AspNetCore.SwaggerGen.Test/SwaggerGenerator/OpenApiSchemaExtensionsTests.cs

@@ -1,4 +1,5 @@
-using System.ComponentModel.DataAnnotations;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
 using System.Globalization;
 using Microsoft.OpenApi;
 
@@ -149,6 +150,189 @@ public static void ApplyValidationAttributes_Handles_DataTypeAttribute_CustomDat
         Assert.Equal(customDataType, schema.Format);
     }
 
+    [Fact]
+    public static void ApplyValidationAttributes_MinLength_On_Dictionary_Maps_To_MinProperties()
+    {
+        // Arrange - dictionary schema is represented as an Object with AdditionalProperties
+        var schema = new OpenApiSchema
+        {
+            Type = JsonSchemaType.Object,
+            AdditionalPropertiesAllowed = true,
+            AdditionalProperties = new OpenApiSchema { Type = JsonSchemaType.String },
+        };
+
+        // Act
+        schema.ApplyValidationAttributes([new MinLengthAttribute(1)]);
+
+        // Assert
+        Assert.Equal(1, schema.MinProperties);
+        Assert.Null(schema.MinLength);
+        Assert.Null(schema.MinItems);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_MaxLength_On_Dictionary_Maps_To_MaxProperties()
+    {
+        // Arrange
+        var schema = new OpenApiSchema
+        {
+            Type = JsonSchemaType.Object,
+            AdditionalPropertiesAllowed = true,
+            AdditionalProperties = new OpenApiSchema { Type = JsonSchemaType.String },
+        };
+
+        // Act
+        schema.ApplyValidationAttributes([new MaxLengthAttribute(10)]);
+
+        // Assert
+        Assert.Equal(10, schema.MaxProperties);
+        Assert.Null(schema.MaxLength);
+        Assert.Null(schema.MaxItems);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_Length_On_Dictionary_Maps_To_Min_And_MaxProperties()
+    {
+        // Arrange
+        var schema = new OpenApiSchema
+        {
+            Type = JsonSchemaType.Object,
+            AdditionalPropertiesAllowed = true,
+            AdditionalProperties = new OpenApiSchema { Type = JsonSchemaType.String },
+        };
+
+        // Act
+        schema.ApplyValidationAttributes([new LengthAttribute(2, 5)]);
+
+        // Assert
+        Assert.Equal(2, schema.MinProperties);
+        Assert.Equal(5, schema.MaxProperties);
+        Assert.Null(schema.MinLength);
+        Assert.Null(schema.MaxLength);
+        Assert.Null(schema.MinItems);
+        Assert.Null(schema.MaxItems);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_MinLength_On_String_Still_Maps_To_MinLength()
+    {
+        // Arrange - regression guard for the existing string path
+        var schema = new OpenApiSchema { Type = JsonSchemaType.String };
+
+        // Act
+        schema.ApplyValidationAttributes([new MinLengthAttribute(3)]);
+
+        // Assert
+        Assert.Equal(3, schema.MinLength);
+        Assert.Null(schema.MinProperties);
+        Assert.Null(schema.MinItems);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_MinLength_On_Array_Still_Maps_To_MinItems()
+    {
+        // Arrange - regression guard for the existing array path
+        var schema = new OpenApiSchema { Type = JsonSchemaType.Array };
+
+        // Act
+        schema.ApplyValidationAttributes([new MinLengthAttribute(3)]);
+
+        // Assert
+        Assert.Equal(3, schema.MinItems);
+        Assert.Null(schema.MinProperties);
+        Assert.Null(schema.MinLength);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_MaxLength_On_String_Still_Maps_To_MaxLength()
+    {
+        var schema = new OpenApiSchema { Type = JsonSchemaType.String };
+
+        schema.ApplyValidationAttributes([new MaxLengthAttribute(5)]);
+
+        Assert.Equal(5, schema.MaxLength);
+        Assert.Null(schema.MaxProperties);
+        Assert.Null(schema.MaxItems);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_MaxLength_On_Array_Still_Maps_To_MaxItems()
+    {
+        var schema = new OpenApiSchema { Type = JsonSchemaType.Array };
+
+        schema.ApplyValidationAttributes([new MaxLengthAttribute(5)]);
+
+        Assert.Equal(5, schema.MaxItems);
+        Assert.Null(schema.MaxProperties);
+        Assert.Null(schema.MaxLength);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_Length_On_String_Still_Maps_To_MinAndMaxLength()
+    {
+        var schema = new OpenApiSchema { Type = JsonSchemaType.String };
+
+        schema.ApplyValidationAttributes([new LengthAttribute(1, 5)]);
+
+        Assert.Equal(1, schema.MinLength);
+        Assert.Equal(5, schema.MaxLength);
+        Assert.Null(schema.MinProperties);
+        Assert.Null(schema.MaxProperties);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_Length_On_Array_Still_Maps_To_MinAndMaxItems()
+    {
+        var schema = new OpenApiSchema { Type = JsonSchemaType.Array };
+
+        schema.ApplyValidationAttributes([new LengthAttribute(1, 5)]);
+
+        Assert.Equal(1, schema.MinItems);
+        Assert.Equal(5, schema.MaxItems);
+        Assert.Null(schema.MinProperties);
+        Assert.Null(schema.MaxProperties);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_MinLength_On_EnumKeyedDictionarySchema_Maps_To_MinProperties()
+    {
+        // Enum-keyed dictionaries are emitted as Object with known Properties and
+        // AdditionalPropertiesAllowed = false (see SchemaGenerator.CreateDictionarySchema).
+        // The fix must still route MinLength to MinProperties in this shape.
+        var schema = new OpenApiSchema
+        {
+            Type = JsonSchemaType.Object,
+            Properties = new Dictionary<string, IOpenApiSchema>
+            {
+                ["Foo"] = new OpenApiSchema { Type = JsonSchemaType.String },
+                ["Bar"] = new OpenApiSchema { Type = JsonSchemaType.String },
+            },
+            AdditionalPropertiesAllowed = false,
+        };
+
+        schema.ApplyValidationAttributes([new MinLengthAttribute(1)]);
+
+        Assert.Equal(1, schema.MinProperties);
+        Assert.Null(schema.MinLength);
+    }
+
+    [Fact]
+    public static void ApplyValidationAttributes_MinLength_On_NullableObjectSchema_Maps_To_MinProperties()
+    {
+        // A nullable dictionary has Type = Object | Null. HasFlag(Object) must still route to MinProperties.
+        var schema = new OpenApiSchema
+        {
+            Type = JsonSchemaType.Object | JsonSchemaType.Null,
+            AdditionalPropertiesAllowed = true,
+            AdditionalProperties = new OpenApiSchema { Type = JsonSchemaType.String },
+        };
+
+        schema.ApplyValidationAttributes([new MinLengthAttribute(2)]);
+
+        Assert.Equal(2, schema.MinProperties);
+        Assert.Null(schema.MinLength);
+    }
+
     private sealed class CultureSwitcher : IDisposable
     {
         private readonly CultureInfo _previous;

test/Swashbuckle.AspNetCore.TestSupport/Fixtures/TypeWithValidationAttributes.cs

@@ -1,4 +1,5 @@
-using System.ComponentModel;
+using System.Collections.Generic;
+using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
 
 namespace Swashbuckle.AspNetCore.TestSupport;
@@ -14,12 +15,18 @@ public class TypeWithValidationAttributes
     [MinLength(1), MaxLength(3)]
     public string[] ArrayWithMinMaxLength { get; set; }
 
+    [MinLength(1), MaxLength(3)]
+    public IReadOnlyDictionary<string, string> IReadOnlyDictionaryWithMinMaxLength { get; set; }
+
     [Length(1, 3)]
     public string StringWithLength { get; set; }
 
     [Length(1, 3)]
     public string[] ArrayWithLength { get; set; }
 
+    [Length(1, 3)]
+    public Dictionary<string, string> DictionaryWithLengthAttribute { get; set; }
+
     [Range(1, 10, MinimumIsExclusive = true, MaximumIsExclusive = true)]
     public int IntWithExclusiveRange { get; set; }
 

test/Swashbuckle.AspNetCore.TestSupport/Fixtures/TypeWithValidationAttributesViaMetadataType.cs

@@ -1,4 +1,5 @@
-using System.ComponentModel;
+using System.Collections.Generic;
+using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
 using Microsoft.AspNetCore.Mvc;
 
@@ -13,10 +14,14 @@ public class TypeWithValidationAttributesViaMetadataType
 
     public string[] ArrayWithMinMaxLength { get; set; }
 
+    public IReadOnlyDictionary<string, string> IReadOnlyDictionaryWithMinMaxLength { get; set; }
+
     public string StringWithLength { get; set; }
 
     public string[] ArrayWithLength { get; set; }
 
+    public Dictionary<string, string> DictionaryWithLengthAttribute { get; set; }
+
     public string StringWithBase64 { get; set; }
 
     public double IntWithExclusiveRange { get; set; }
@@ -49,12 +54,18 @@ public class MetadataType
     [MinLength(1), MaxLength(3)]
     public string[] ArrayWithMinMaxLength { get; set; }
 
+    [MinLength(1), MaxLength(3)]
+    public IReadOnlyDictionary<string, string> IReadOnlyDictionaryWithMinMaxLength { get; set; }
+
     [Length(1, 3)]
     public string StringWithLength { get; set; }
 
     [Length(1, 3)]
     public string[] ArrayWithLength { get; set; }
 
+    [Length(1, 3)]
+    public Dictionary<string, string> DictionaryWithLengthAttribute { get; set; }
+
     [Range(1, 10, MinimumIsExclusive = true, MaximumIsExclusive = true)]
     public int IntWithExclusiveRange { get; set; }