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

[WanjohiSammy]

Assemblies affected
8.x

Describe the bug
The ODataEnumSerializer and ODataEnumDeserializer fails to convert multi-value Flag enums to LowerCamelCase as specified in EnumMember attribute. However, this works with single-value Flag enums.

Example:

Consider the following Flag enum:

[Flags]
[DataContract(Name = "exampleEnum")]
public enum ExampleEnum
{
    [EnumMember(Value = "firstValue")]
    FirstValue = 1,

    [EnumMember(Value = "secondValue")]
    SecondValue = 2,

    [EnumMember(Value = "thirdValue")]
    ThirdValue = 4
}

With the default ODataEnumSerializer, a single-value Flag enum like ExampleEnum.FirstValue is correctly converted to ("firstValue"). However, a multi-value Flag enum like ExampleEnum.FirstValue | ExampleEnum.SecondValue is not converted to ("firstValue, secondValue") as expected. Instead, it remains in its original form as "FirstValue, SecondValue"

Reproduce steps

1. Clone the repo

   git clone https://github.com/WanjohiSammy/ODataWebApiApplicationSample.git

2. Build and run the application

3. Find the ODataWebApiApplication15.http and execute the following requests:

   • GET /odata/Customers:
     Note that the customerType for customer id=1 is "regular" but the customerType for customer id=2 is "Premium, VIP" instead of "premium, vip" in lower camel case

     {
       "@odata.context": "https://localhost:7085/odata/$metadata#Customers",
       "value": [
         {
           "id": 1,
           "name": "Customer1",
           "customerType": "regular"
         },
         {
           "id": 2,
           "name": "Customer2",
           "customerType": "Premium, VIP"
         },
         ...
       ]
     }

   • POST /odata/Customers

     • With "customerType": "Regular, Premium" - a new record is created successfully

     • With lower camel case "customerType": "regular, premium" - request is null

         {
            "Id": 0,
            "Name": "John Doe",
            "CustomerType": "regular, premium"
         }

     • With lower camel case single-value "customerType": "regular" - works as expected

       {
          "id": 0,
          "name": "John Doe",
          "customerType": "regular"
       }

   • PATCH /odata/Customers(2)

     • With "customerType": "Regular, VIP" - the record is updated successfully
     • With lower camel case "customerType": "regular, premium" - delta is null

       {
          "CustomerType": "regular, premium"
       }

     • With lower camel case single-value "customerType": "regular" - works as expected

       {
          "customerType": "vip"
       }

Data Model

EDM (CSDL) Model

<edmx:Edmx xmlns:edmx="http://docs.oasis-open.org/odata/ns/edmx" Version="4.0">
	<edmx:DataServices>
		<Schema xmlns="http://docs.oasis-open.org/odata/ns/edm" Namespace="NS">
			<EntityType Name="customer">
				<Key>
					<PropertyRef Name="id" />
				</Key>
				<Property Name="id" Type="Edm.Int32" Nullable="false" />
				<Property Name="name" Type="Edm.String" />
				<Property Name="customerType" Type="NS.customerType" />
				<NavigationProperty Name="orders" Type="Collection(NS.Order)" />
			</EntityType>
			<EntityType Name="Order">
				<Key>
					<PropertyRef Name="Id" />
				</Key>
				<Property Name="Id" Type="Edm.Int32" Nullable="false" />
				<Property Name="Amount" Type="Edm.Decimal" Nullable="false" Scale="Variable" />
			</EntityType>
			<EnumType Name="customerType" IsFlags="true">
				<Member Name="regular" Value="1" />
				<Member Name="premium" Value="2" />
				<Member Name="vip" Value="4" />
			</EnumType>
			<Function Name="GetCustomerOrdersTotalAmount" IsBound="true">
				<Parameter Name="bindingParameter" Type="NS.customer" />
				<ReturnType Type="Edm.Int32" Nullable="false" />
			</Function>
			<Function Name="GetCustomerByName" IsBound="true">
				<Parameter Name="bindingParameter" Type="Collection(NS.customer)" />
				<Parameter Name="name" Type="Edm.String" />
				<ReturnType Type="NS.customer" />
			</Function>
			<EntityContainer Name="Container">
				<EntitySet Name="Customers" EntityType="NS.customer">
					<NavigationPropertyBinding Path="orders" Target="Orders" />
				</EntitySet>
				<EntitySet Name="Orders" EntityType="NS.Order" />
			</EntityContainer>
		</Schema>
	</edmx:DataServices>
</edmx:Edmx>

Request/Response

###
GET {{HostAddress}}/odata/Customers
Accept: application/json

###
POST {{HostAddress}}/odata/Customers
Content-Type: application/json

{
   "id": 0,
   "name": "John Doe",
   "customerType": "regular"
}

###
PATCH {{HostAddress}}/odata/Customers(2)
Content-Type: application/json

{
  "customerType": "vip"
}

Expected behavior
Expected lower camel case for multi-value Flag enum to work the same way as for single-value. For example, firstValue, secondValue should work the same way firstValue.