Only list enums when a flag attribute is pressent, fixes #478

SpotifyAPI.Web.Tests/Models/RequestParamsTest.cs

@@ -45,6 +45,32 @@ namespace SpotifyAPI.Web.Tests
       first.List.Add("hello_world");
       Assert.AreEqual(new Dictionary<string, string> { { "list", "hello_world" } }, first.BuildQueryParams());
     }
+
+    [Test]
+    public void EnumWithoutFlagsDoesNotHaveMultipleValues()
+    {
+      var enumModel = new EnumWithoutFlagsRequestModel
+      {
+        AnEnumParam = EnumWithoutFlagsRequestModel.AnEnum.Two
+      };
+
+      var result = enumModel.BuildQueryParams();
+      Assert.AreEqual(1, result.Keys.Count);
+      Assert.AreEqual("two", result["an_enum"]);
+    }
+
+    [Test]
+    public void EnumWithFlagsDoesHaveMultipleValues()
+    {
+      var enumModel = new EnumWitFlagsRequestModel
+      {
+        AnEnumParam = EnumWitFlagsRequestModel.AnEnum.Two | EnumWitFlagsRequestModel.AnEnum.One
+      };
+
+      var result = enumModel.BuildQueryParams();
+      Assert.AreEqual(1, result.Keys.Count);
+      Assert.AreEqual("one,two", result["an_enum"]);
+    }
   }
 
   public class FirstRequestModel : RequestParams
@@ -66,4 +92,35 @@ namespace SpotifyAPI.Web.Tests
     [QueryParam("list")]
     public IList<string> List { get; set; } = new List<string>();
   }
+
+  public class EnumWithoutFlagsRequestModel : RequestParams
+  {
+    [QueryParam("an_enum")]
+    public AnEnum AnEnumParam { get; set; }
+
+    public enum AnEnum
+    {
+      [String("one")]
+      One,
+
+      [String("two")]
+      Two,
+    }
+  }
+
+  public class EnumWitFlagsRequestModel : RequestParams
+  {
+    [QueryParam("an_enum")]
+    public AnEnum AnEnumParam { get; set; }
+
+    [Flags]
+    public enum AnEnum
+    {
+      [String("one")]
+      One = 1,
+
+      [String("two")]
+      Two = 2,
+    }
+  }
 }

SpotifyAPI.Web/Models/Request/ArtistsAlbumsRequest.cs

@@ -41,17 +41,17 @@ namespace SpotifyAPI.Web
     public enum IncludeGroups
     {
       [String("album")]
-      Album,
+      Album = 1,
 
       [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1720")]
       [String("single")]
-      Single,
+      Single = 2,
 
       [String("appears_on")]
-      AppearsOn,
+      AppearsOn = 4,
 
       [String("compilation")]
-      Compilation
+      Compilation = 8,
     }
   }
 }

SpotifyAPI.Web/Models/Request/RequestParams.cs

@@ -114,19 +114,26 @@ namespace SpotifyAPI.Web
           var enumType = valueAsEnum.GetType();
           var valueList = new List<string>();
 
-          foreach (Enum enumVal in Enum.GetValues(valueAsEnum.GetType()))
+          if (enumType.IsDefined(typeof(FlagsAttribute), false))
           {
-            if (valueAsEnum.HasFlag(enumVal))
+            foreach (Enum enumVal in Enum.GetValues(valueAsEnum.GetType()))
             {
-              if (enumType
-                .GetMember(enumVal.ToString())[0]
-                .GetCustomAttributes(typeof(StringAttribute))
-                .FirstOrDefault() is StringAttribute stringAttr)
+              if (valueAsEnum.HasFlag(enumVal))
               {
-                valueList.Add(stringAttr.Value);
+                if (StringAttribute.GetValue(enumType, enumVal, out var stringVal))
+                {
+                  valueList.Add(stringVal);
+                }
               }
             }
           }
+          else
+          {
+            if (StringAttribute.GetValue(enumType, valueAsEnum, out var stringVal))
+            {
+              valueList.Add(stringVal);
+            }
+          }
           queryParams.Add(attribute.Key ?? prop.Name, string.Join(",", valueList));
         }
         else

SpotifyAPI.Web/Util/StringAttribute.cs

@@ -1,4 +1,7 @@
 using System;
+using System.Reflection;
+using System.Linq;
+using System.Diagnostics.CodeAnalysis;
 
 namespace SpotifyAPI.Web
 {
@@ -11,5 +14,27 @@ namespace SpotifyAPI.Web
     }
 
     public string Value { get; set; }
+
+#if NETSTANDARD2_1
+    public static bool GetValue(Type enumType, Enum enumValue, [NotNullWhen(true)] out string? result)
+#endif
+#if NETSTANDARD2_0
+    public static bool GetValue(Type enumType, Enum enumValue, out string? result)
+#endif
+    {
+      Ensure.ArgumentNotNull(enumType, nameof(enumType));
+      Ensure.ArgumentNotNull(enumValue, nameof(enumValue));
+
+      if (enumType
+        .GetMember(enumValue.ToString())[0]
+        .GetCustomAttributes(typeof(StringAttribute))
+        .FirstOrDefault() is StringAttribute stringAttr)
+      {
+        result = stringAttr.Value;
+        return true;
+      }
+      result = null;
+      return false;
+    }
   }
 }