From c9eb9ddc89be507d762a0af08734fb90cdcde812 Mon Sep 17 00:00:00 2001
From: rmorris <richard.morris@gettyimages.com>
Date: Sat, 6 Mar 2021 08:18:33 +0000
Subject: [PATCH] Support DefaultValueAttribute on parameter-based schemas

---
 .../SchemaGenerator/SchemaGenerator.cs          | 12 +++++++++---
 .../JsonSerializerSchemaGeneratorTests.cs       | 17 ++++++++++++++++-
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/Swashbuckle.AspNetCore.SwaggerGen/SchemaGenerator/SchemaGenerator.cs b/src/Swashbuckle.AspNetCore.SwaggerGen/SchemaGenerator/SchemaGenerator.cs
index f71fea83d..922ab81e8 100644
--- a/src/Swashbuckle.AspNetCore.SwaggerGen/SchemaGenerator/SchemaGenerator.cs
+++ b/src/Swashbuckle.AspNetCore.SwaggerGen/SchemaGenerator/SchemaGenerator.cs
@@ -112,13 +112,19 @@ private OpenApiSchema GenerateSchemaForParameter(ParameterInfo parameterInfo, Sc
 
             if (schema.Reference == null)
             {
-                if (parameterInfo.HasDefaultValue)
+                var customAttributes = parameterInfo.GetCustomAttributes();
+
+                var defaultValue = parameterInfo.HasDefaultValue
+                    ? parameterInfo.DefaultValue
+                    : customAttributes.OfType<DefaultValueAttribute>().FirstOrDefault()?.Value;
+
+                if (defaultValue != null)
                 {
-                    var defaultAsJson = dataContract.JsonConverter(parameterInfo.DefaultValue);
+                    var defaultAsJson = dataContract.JsonConverter(defaultValue);
                     schema.Default = OpenApiAnyFactory.CreateFromJson(defaultAsJson);
                 }
 
-                schema.ApplyValidationAttributes(parameterInfo.GetCustomAttributes());
+                schema.ApplyValidationAttributes(customAttributes);
 
                 ApplyFilters(schema, parameterInfo.ParameterType, schemaRepository, parameterInfo: parameterInfo);
             }
diff --git a/test/Swashbuckle.AspNetCore.SwaggerGen.Test/SchemaGenerator/JsonSerializerSchemaGeneratorTests.cs b/test/Swashbuckle.AspNetCore.SwaggerGen.Test/SchemaGenerator/JsonSerializerSchemaGeneratorTests.cs
index a761f0627..bd2ea2912 100644
--- a/test/Swashbuckle.AspNetCore.SwaggerGen.Test/SchemaGenerator/JsonSerializerSchemaGeneratorTests.cs
+++ b/test/Swashbuckle.AspNetCore.SwaggerGen.Test/SchemaGenerator/JsonSerializerSchemaGeneratorTests.cs
@@ -12,7 +12,6 @@
 using Xunit;
 using Swashbuckle.AspNetCore.TestSupport;
 using Microsoft.OpenApi.Any;
-using System.Collections.ObjectModel;
 
 namespace Swashbuckle.AspNetCore.SwaggerGen.Test
 {
@@ -334,6 +333,22 @@ public void GenerateSchema_SetsReadOnlyAndWriteOnlyFlags_IfPropertyIsRestricted(
             Assert.True(schema.Properties["WriteOnlyProperty"].WriteOnly);
         }
 
+        [Fact]
+        public void GenerateSchema_SetsDefault_IfParameterHasDefaultValueAttribute()
+        {
+            var schemaRepository = new SchemaRepository();
+
+            var parameterInfo = typeof(FakeController)
+                .GetMethod(nameof(FakeController.ActionWithIntParameterWithDefaultValueAttribute))
+                .GetParameters()
+                .First();
+
+            var schema = Subject().GenerateSchema(parameterInfo.ParameterType, schemaRepository, parameterInfo: parameterInfo);
+
+            Assert.NotNull(schema.Default);
+            Assert.Equal("3", schema.Default.ToJson());
+        }
+
         [Theory]
         [InlineData(typeof(ComplexType), typeof(ComplexType), "string")]
         [InlineData(typeof(GenericType<int, string>), typeof(GenericType<int, string>), "string")]