Fix Default ODataEnumSerializer and ODataEnumDeserializer Fails to Convert Multi-Value Flag Enum Values to Lower Camel Case

src/Microsoft.AspNetCore.OData/Formatter/Deserialization/ODataEnumDeserializer.cs

@@ -9,10 +9,12 @@
 using System.Diagnostics.Contracts;
 using System.Linq;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.OData.Common;
 using Microsoft.AspNetCore.OData.Edm;
 using Microsoft.AspNetCore.OData.Formatter.Value;
 using Microsoft.OData;
 using Microsoft.OData.Edm;
+using Microsoft.OData.ModelBuilder;
 
 namespace Microsoft.AspNetCore.OData.Formatter.Deserialization;
 
@@ -83,6 +85,8 @@ public override object ReadInline(object item, IEdmTypeReference edmType, ODataD
 
         IEdmEnumType enumType = enumTypeReference.EnumDefinition();
 
+        Type clrType = readContext.Model.GetClrType(edmType);
+
         // Enum member supports model alias case. So, try to use the Edm member name to retrieve the Enum value.
         var memberMapAnnotation = readContext.Model.GetClrEnumMemberAnnotation(enumType);
         if (memberMapAnnotation != null)
@@ -98,10 +102,89 @@ public override object ReadInline(object item, IEdmTypeReference edmType, ODataD
                         return clrMember;
                     }
                 }
+                else if (enumType.IsFlags)
+                {
+                    var result = ReadFlagsEnumValue(enumValue, enumType, clrType, memberMapAnnotation);
+                    if (result != null)
+                    {
+                        return result;
+                    }
+                }
             }
         }
 
-        Type clrType = readContext.Model.GetClrType(edmType);
         return EnumDeserializationHelpers.ConvertEnumValue(item, clrType);
     }
+
+    /// <summary>
+    /// Reads the value of a flags enum.
+    /// </summary>
+    /// <param name="enumValue">The OData enum value.</param>
+    /// <param name="enumType">The EDM enum type.</param>
+    /// <param name="clrType">The EDM enum CLR type.</param>
+    /// <param name="memberMapAnnotation">The annotation containing the mapping of CLR enum members to EDM enum members.</param>
+    /// <returns>The deserialized flags enum value.</returns>
+    private static object ReadFlagsEnumValue(ODataEnumValue enumValue, IEdmEnumType enumType, Type clrType, ClrEnumMemberAnnotation memberMapAnnotation)
+    {
+        long result = 0;
+        clrType = TypeHelper.GetUnderlyingTypeOrSelf(clrType);
+
+        ReadOnlySpan<char> source = enumValue.Value.AsSpan().Trim();
+        int start = 0;
+        while (start < source.Length)
+        {
+            // Find the end of the current value.
+            int end = start;
+            while (end < source.Length && source[end] != ',')
+            {
+                end++;
+            }
+
+            // Extract the current value.
+            ReadOnlySpan<char> currentValue = source[start..end].Trim();
+
+            bool parsed = Enum.TryParse(clrType, currentValue, true, out object enumMemberParsed);
+            if (parsed)
+            {
+                result |= Convert.ToInt64((Enum)enumMemberParsed);
+            }
+            else
+            {
+                // If the value is not a valid enum member, try to match it with the EDM enum member name.
+                // This is needed for model alias case.
+                // For example,
+                // - if the enum member is defined as "Friday" and the value is "fri", we need to match them.
+                // - if the enum member is defined as "FullTime" and the value is "Full Time", we need to match them.
+                // - if the enum member is defined as "PartTime" and the value is "part time", we need to match them.
+                foreach (IEdmEnumMember enumMember in enumType.Members)
+                {
+                    // Check if the current value matches the enum member name.
+                    parsed = currentValue.Equals(enumMember.Name.AsSpan(), StringComparison.InvariantCultureIgnoreCase);
+                    if (parsed)
+                    {
+                        Enum clrEnumMember = memberMapAnnotation.GetClrEnumMember(enumMember);
+                        if(clrEnumMember != null)
+                        {
+                            result |= Convert.ToInt64(clrEnumMember);
+                            break;
+                        }
+
+                        // If the enum member is not found, the value is not valid.
+                        parsed = false;
+                    }
+                }
+            }
+
+            // If still not valid, return null.
+            if (!parsed)
+            {
+                return null;
+            }
+
+            // Move to the next value.
+            start = end + 1;
+        }
+
+        return result == 0 ? null : Enum.ToObject(clrType, result);
+    }
 }

src/Microsoft.AspNetCore.OData/Formatter/Serialization/ODataEnumSerializer.cs

@@ -6,13 +6,15 @@
 //------------------------------------------------------------------------------
 
 using System;
+using System.Collections.Generic;
 using System.Diagnostics.Contracts;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.OData.Common;
 using Microsoft.AspNetCore.OData.Edm;
 using Microsoft.AspNetCore.OData.Formatter.Value;
 using Microsoft.OData;
 using Microsoft.OData.Edm;
+using Microsoft.OData.ModelBuilder;
 
 namespace Microsoft.AspNetCore.OData.Formatter.Serialization;
 
@@ -102,11 +104,18 @@ public virtual ODataEnumValue CreateODataEnumValue(object graph, IEdmEnumTypeRef
         var memberMapAnnotation = writeContext?.Model.GetClrEnumMemberAnnotation(enumType.EnumDefinition());
         if (memberMapAnnotation != null)
         {
-            var edmEnumMember = memberMapAnnotation.GetEdmEnumMember((Enum)graph);
+            Enum graphEnum = (Enum)graph;
+
+            var edmEnumMember = memberMapAnnotation.GetEdmEnumMember(graphEnum);
             if (edmEnumMember != null)
             {
                 value = edmEnumMember.Name;
             }
+            // If the enum is a flags enum, we need to handle the case where multiple flags are set
+            else if (enumType.EnumDefinition().IsFlags)
+            {
+                value = GetFlagsEnumValue(graphEnum, memberMapAnnotation);
+            }
         }
 
         ODataEnumValue enumValue = new ODataEnumValue(value, enumType.FullName());
@@ -171,4 +180,37 @@ private static bool ShouldSuppressTypeNameSerialization(ODataMetadataLevel metad
                 return false;
         }
     }
+
+    /// <summary>
+    /// Gets the combined names of the flags set in a Flags enum value.
+    /// </summary>
+    /// <param name="graphEnum">The enum value.</param>
+    /// <param name="memberMapAnnotation">The annotation containing the mapping of CLR enum members to EDM enum members.</param>
+    /// <returns>A comma-separated string of the names of the flags that are set.</returns>
+    private static string GetFlagsEnumValue(Enum graphEnum, ClrEnumMemberAnnotation memberMapAnnotation)
+    {
+        List<string> flagsList = new List<string>();
+
+        // Convert the enum value to a long for bitwise operations
+        long graphValue = Convert.ToInt64(graphEnum);
+
+        // Iterate through all enum values
+        foreach (Enum flag in Enum.GetValues(graphEnum.GetType()))
+        {
+            // Convert the current flag to a long
+            long flagValue = Convert.ToInt64(flag);
+
+            // Using bitwise operations to check if a flag is set, which is more efficient than Enum.HasFlag
+            if ((graphValue & flagValue) != 0 && flagValue != 0)
+            {
+                IEdmEnumMember flagMember = memberMapAnnotation.GetEdmEnumMember(flag);
+                if (flagMember != null)
+                {
+                    flagsList.Add(flagMember.Name);
+                }
+            }
+        }
+
+        return string.Join(", ", flagsList);
+    }
 }

src/Microsoft.AspNetCore.OData/Microsoft.AspNetCore.OData.xml

@@ -3522,6 +3522,16 @@
         <member name="M:Microsoft.AspNetCore.OData.Formatter.Deserialization.ODataEnumDeserializer.ReadInline(System.Object,Microsoft.OData.Edm.IEdmTypeReference,Microsoft.AspNetCore.OData.Formatter.Deserialization.ODataDeserializerContext)">
             <inheritdoc />
         </member>
+        <member name="M:Microsoft.AspNetCore.OData.Formatter.Deserialization.ODataEnumDeserializer.ReadFlagsEnumValue(Microsoft.OData.ODataEnumValue,Microsoft.OData.Edm.IEdmEnumType,System.Type,Microsoft.OData.ModelBuilder.ClrEnumMemberAnnotation)">
+            <summary>
+            Reads the value of a flags enum.
+            </summary>
+            <param name="enumValue">The OData enum value.</param>
+            <param name="enumType">The EDM enum type.</param>
+            <param name="clrType">The EDM enum CLR type.</param>
+            <param name="memberMapAnnotation">The annotation containing the mapping of CLR enum members to EDM enum members.</param>
+            <returns>The deserialized flags enum value.</returns>
+        </member>
         <member name="T:Microsoft.AspNetCore.OData.Formatter.Deserialization.ODataPrimitiveDeserializer">
             <summary>
             Represents an <see cref="T:Microsoft.AspNetCore.OData.Formatter.Deserialization.ODataDeserializer"/> that can read OData primitive types.
@@ -4651,6 +4661,14 @@
             <param name="writeContext">The serializer write context.</param>
             <returns>The created <see cref="T:Microsoft.OData.ODataEnumValue"/>.</returns>
         </member>
+        <member name="M:Microsoft.AspNetCore.OData.Formatter.Serialization.ODataEnumSerializer.GetFlagsEnumValue(System.Enum,Microsoft.OData.ModelBuilder.ClrEnumMemberAnnotation)">
+            <summary>
+            Gets the combined names of the flags set in a Flags enum value.
+            </summary>
+            <param name="graphEnum">The enum value.</param>
+            <param name="memberMapAnnotation">The annotation containing the mapping of CLR enum members to EDM enum members.</param>
+            <returns>A comma-separated string of the names of the flags that are set.</returns>
+        </member>
         <member name="T:Microsoft.AspNetCore.OData.Formatter.Serialization.ODataErrorSerializer">
             <summary>
             Represents an <see cref="T:Microsoft.AspNetCore.OData.Formatter.Serialization.ODataSerializer"/> to serialize <see cref="T:Microsoft.OData.ODataError"/>s.

test/Microsoft.AspNetCore.OData.E2E.Tests/Enums/EnumsController.cs

@@ -12,7 +12,6 @@
 using Microsoft.AspNetCore.OData.Deltas;
 using Microsoft.AspNetCore.OData.Formatter;
 using Microsoft.AspNetCore.OData.Query;
-using Microsoft.AspNetCore.OData.Routing.Attributes;
 using Microsoft.AspNetCore.OData.Routing.Controllers;
 using Xunit;
 
@@ -46,6 +45,7 @@ private void InitEmployees()
                 SkillSet=new List<Skill> { Skill.CSharp, Skill.Sql },
                 Gender=Gender.Female,
                 AccessLevel=AccessLevel.Execute,
+                EmployeeType = EmployeeType.FullTime | EmployeeType.PartTime,
                 FavoriteSports=new FavoriteSports()
                 {
                     LikeMost=Sport.Pingpong,
@@ -58,6 +58,7 @@ private void InitEmployees()
                 SkillSet=new List<Skill>(),
                 Gender=Gender.Female,
                 AccessLevel=AccessLevel.Read,
+                EmployeeType = EmployeeType.Contract,
                 FavoriteSports=new FavoriteSports()
                 {
                     LikeMost=Sport.Pingpong,
@@ -70,6 +71,7 @@ private void InitEmployees()
                 SkillSet=new List<Skill> { Skill.Web, Skill.Sql },
                 Gender=Gender.Female,
                 AccessLevel=AccessLevel.Read|AccessLevel.Write,
+                EmployeeType = EmployeeType.Intern | EmployeeType.FullTime | EmployeeType.PartTime,
                 FavoriteSports=new FavoriteSports()
                 {
                     LikeMost=Sport.Pingpong|Sport.Basketball,
@@ -121,6 +123,13 @@ public IActionResult GetFavoriteSportsFromEmployee(int key)
         return Ok(employee.FavoriteSports);
     }
 
+    [EnableQuery]
+    public IActionResult GetEmployeeTypeFromEmployee(int key)
+    {
+        var employee = Employees.SingleOrDefault(e => e.ID == key);
+        return Ok(employee.EmployeeType);
+    }
+
     [HttpGet("Employees({key})/FavoriteSports/LikeMost")]
     public IActionResult GetFavoriteSportLikeMost(int key)
     {

test/Microsoft.AspNetCore.OData.E2E.Tests/Enums/EnumsDataModel.cs

@@ -23,6 +23,8 @@ public class Employee
 
     public AccessLevel AccessLevel { get; set; }
 
+    public EmployeeType EmployeeType { get; set; }
+
     public FavoriteSports FavoriteSports { get; set; }
 }
 
@@ -36,6 +38,23 @@ public enum AccessLevel
     Execute = 4
 }
 
+[Flags]
+[DataContract(Name = "employeeType")]
+public enum EmployeeType
+{
+    [EnumMember(Value = "full time")]
+    FullTime = 1,
+
+    [EnumMember(Value = "Part Time")]
+    PartTime = 2,
+
+    [EnumMember(Value = "contract")]
+    Contract = 4,
+
+    [EnumMember(Value = "intern")]
+    Intern = 8
+}
+
 public enum Gender
 {
     Male = 1,

test/Microsoft.AspNetCore.OData.E2E.Tests/Enums/EnumsEdmModel.cs

@@ -21,6 +21,7 @@ public static IEdmModel GetExplicitModel()
         employee.CollectionProperty<Skill>(c => c.SkillSet);
         employee.EnumProperty<Gender>(c => c.Gender);
         employee.EnumProperty<AccessLevel>(c => c.AccessLevel);
+        employee.EnumProperty<EmployeeType>(c => c.EmployeeType);
         employee.ComplexProperty<FavoriteSports>(c => c.FavoriteSports);
 
         var skill = builder.EnumType<Skill>();
@@ -37,6 +38,12 @@ public static IEdmModel GetExplicitModel()
         accessLevel.Member(AccessLevel.Read);
         accessLevel.Member(AccessLevel.Write);
 
+        var employeeType = builder.EnumType<EmployeeType>();
+        employeeType.Member(EmployeeType.FullTime);
+        employeeType.Member(EmployeeType.PartTime);
+        employeeType.Member(EmployeeType.Contract);
+        employeeType.Member(EmployeeType.Intern);
+
         var favoriteSports = builder.ComplexType<FavoriteSports>();
         favoriteSports.EnumProperty<Sport>(f => f.LikeMost);
         favoriteSports.CollectionProperty<Sport>(f => f.Like);