Skip to content

evolvable-enums.md

Latest commit

 

History

History
490 lines (388 loc) · 16.1 KB

evolvable-enums.md

File metadata and controls

490 lines (388 loc) · 16.1 KB

Evolvable Enums

Microsoft Graph API Design Pattern

The evolvable enum pattern allows API producers to extend enumerated types with new members without breaking API consumers.

Problem

Frequently API producers want to add new members to an enum type after it is initially published. Some serialization libraries may fail when they encounter members in an enum type that were added after the serialization model was generated. Within this documented we will refer to any added enum members as unknown.

Solution

The solution here is to add a 'sentinel' member named unknownFutureValue at the end of the currently known enum members. The API producer will then replace any member that is numerically after unknownFutureValue with unknownFutureValue. If an API consumer can handle unknown enum values the consumer can opt into receiving the unknown enum members by specifying the Prefer: include-unknown-enum-members HTTP Header in their request(s), the API producer will then indicate that this preference has been applied by returning the Preference-Applied: include-unknown-enum-members HTTP header in the response.

When to Use this Pattern

  • It is a best practice to include a unknownFutureValue value when the enum is initially introduced to allow flexibility to extend the enum during the lifetime of the API. Even if the API producer believes they have included all possible members in an enum it is still strongly recommended to include a unknownFutureValue member to allow for unforeseen future circumstances which may require extending the enum.

  • This pattern must not be used in scenarios where an API consumer wants to use enum members that are not known to the API producer.

Issues and Considerations

  • An enum member with the name of unknownFutureValue must only be used as a sentinel value, an API producer must not include a member named unknownFutureValue in an enum for any other purpose.

  • Changing the value (i.e. position) of the unknownFutureValue sentinel member is considered a breaking change, and must follow the deprecation process.

  • Enum Types can have multiple members with the same numeric value to allow for aliasing enum members, unknownFutureValue must not be aliased to any other enum member.

  • There is no ability for a client to indicate that it can handle a subset of unknown enum members, instead that can only specify either that they can not handle any unknown enum members, or they can handle any unknown enum members.

  • The Prefer: include-unknown-enum-members header applies to all included enums in the request/response, there is no way for an API consumer to apply the behavior to only a subset of enum types.

  • New values must not be inserted into the enum before unknownFutureValue, implementers are recommended to make the numeric value of unknownFutureValue one greater than the last known enum member to ensure there are no gaps into which a new member could be inadvertently added. The exception to this is the case of flagged enums in which case the value of unknownFutureValue should be be next power of 2 value.

  • For flagged enums care should be exercised to ensure that unknownFutureValue is not included in any enum members that represent a combination of other enum members.

  • If the value of a property containing a flag enum contains multiple unknown values they should all be replaced with a single unknownFutureValue value (i.e. there should not have multiple unknownFutureValue values returned).

  • If an API consumer specifies unknownFutureValue for the value of a property in a POST/PUT request or as parameter of an action or function the API producer must reject the request with a 400 Bad Request HTTP status.

  • If an API consumer specifies unknownFutureValue for the value of a property in a PATCH request the API producer must treat the property as if it were absent (i.e. the existing value should not be changed). For the case where the API producer treats PATCH as an upsert the call must be rejected with a 400 Bad Request HTTP status.

  • If an API consumer specifies an enum member greater than unknownFutureValue in any request without specifying the Prefer: include-unknown-enum-members header the API producer must reject the request with a 400 Bad Request HTTP status.

  • For details of how the unknownFutureValue value is handled as part of a $filter clause please consult the following examples:

CSDL

<EntityType Name="example">
    <Property Name="enumProperty" Type="exampleEnum"/>
</EntityType>

<EnumType Name="exampleEnum">
    <Member Name="default" Value="0"/>
    <Member Name="one" Value="1"/>
    <Member Name="unknownFutureValue" Value="2"/>
    <Member Name="newValue" Value="3"/>
</EnumType>

Filter Behavior

$filter clause Prefer: include-unknown-enum-members Absent Prefer: include-unknown-enum-members Present
enumProperty eq unknownFutureValue Return entities where enumProperty has any value greater than unknownFutureValue replacing actual value with unknownFutureValue Return nothing
enumProperty gt unknownFutureValue Return entities where enumProperty has any value greater than unknownFutureValue replacing actual value with unknownFutureValue Return entities where enumProperty has any value greater than unknownFutureValue
enumProperty lt unknownFutureValue Return entities where enumProperty has any known value (i.e. less than unknownFutureValue) Return entities where enumProperty has any value less than unknownFutureValue
enumProperty eq newValue 400 Bad Request Return entities where enumProperty has the value newValue
enumProperty gt newValue 400 Bad Request Return entities where enumProperty has a value greater than newValue
enumProperty lt newValue 400 Bad Request Return entities where enumProperty has a value less than newValue
  • If an evolvable enum is included in an $orderby clause the actual numeric value of the member should be used to order the collection, after sorting the member should then be replaced with unknownFutureValue when the Prefer: include-unknown-enum-members header is absent.

Examples

For the following examples we will consider the managedDevice entity which refers to the managedDeviceArchitecture enum type.

<!-- Simplified entity for example purposes -->
<EntityType Name="managedDevice" BaseType="graph.entity">
    <Property Name="displayName" Type="Edm.String" />
    <Property Name="processorArchitecture" Type="graph.managedDeviceArchitecture"/>
</EntityType>

When the managedDeviceArchitecture enum was initially published to Graph it was defined as below:

<!-- Slightly modified enum for example purposes -->
<EnumType Name="managedDeviceArchitecture">
    <Member Name="unknown" Value="0"/>
    <Member Name="x86" Value="1"/>
    <Member Name="x64" Value="2"/>
    <Member Name="arm" Value="3"/>
    <Member Name="arm64" Value="4"/>
    <Member Name="unknownFutureValue" Value="5"/>
</EnumType>

The enum was later extended to add a new value of quantum leading to the below CSDL

<EnumType Name="managedDeviceArchitecture">
    <Member Name="unknown" Value="0"/>
    <Member Name="x86" Value="1"/>
    <Member Name="x64" Value="2"/>
    <Member Name="arm" Value="3"/>
    <Member Name="arm64" Value="4"/>
    <Member Name="unknownFutureValue" Value="5"/>
    <Member Name="quantum" Value="6"/>
</EnumType>

Default Behavior

GET https://graph.microsoft.com/v1.0/deviceManagement/managedDevices?$select=displayName,processorArchitecture
{
    "value": [
        { 
            "id": "0", 
            "displayName": "Surface Pro X", 
            "processorArchitecture" : "arm64"
        },
        { 
            "id": "1",
            "displayName": "Prototype",
            "processorArchitecture": "unknownFutureValue"
        }
        { 
            "id": "2",
            "displayName": "My Laptop", 
            "processorArchitecture": "x64"
        }
    ]
}

In this case the value of the processorArchitecture property is quantum however since the client did not request the include-unknown-enum-members header the value was replaced with unknownFutureValue

Include opt-in Header

GET https://graph.microsoft.com/v1.0/deviceManagement/managedDevices?$select=displayName,processorArchitecture

Prefer: include-unknown-enum-members
Preference-Applied: include-unknown-enum-members

{
    "value": [
        { 
            "displayName": "Surface Pro X", 
            "processorArchitecture" : "arm64"
        },
        { 
            "displayName": "Prototype",
            "processorArchitecture": "quantum"
        },
        { 
            "displayName": "My Laptop",
            "processorArchitecture": "x64"
        }
    ]
}

Default Sort Behavior

GET https://graph.microsoft.com/v1.0/deviceManagement/managedDevices?$select=displayName,processorArchitecture&$orderBy=processorArchitecture
{
    "value": [
        { 
            "displayName": "Surface Pro X", 
            "processorArchitecture" : "arm64"
        },
        { 
            "displayName": "My Laptop", 
            "processorArchitecture": "x64"
        },
        { 
            "displayName": "Prototype",
            "processorArchitecture": "unknownFutureValue"
        }
    ]
}

Sort Behavior with opt-in Header

GET https://graph.microsoft.com/v1.0/deviceManagement/managedDevices?$select=displayName,processorArchitecture

Prefer: include-unknown-enum-members
Preference-Applied: include-unknown-enum-members

{
    "value": [
        { 
            "displayName": "Surface Pro X",
            "processorArchitecture" : "arm64"
        },
        { 
            "displayName": "My Laptop",
            "processorArchitecture": "x64"
        },
        { 
            "displayName": "Prototype", 
            "processorArchitecture": "quantum"
        }
    ]
}

Default Filter Behavior

GET https://graph.microsoft.com/v1.0/deviceManagement/managedDevices?$select=displayName,processorArchitecture&$filter=processorArchitecture gt x64
{
    "value": [
        { 
            "displayName": "My Laptop", 
            "processorArchitecture": "x64"
        },
        { 
            "displayName": "Prototype",
            "processorArchitecture": "unknownFutureValue"
        }
    ]
}

Filter Behavior with opt-in Header

GET https://graph.microsoft.com/v1.0/deviceManagement/managedDevices?$select=displayName,processorArchitecture&$filter=processorArchitecture gt x64

Prefer: include-unknown-enum-members
Preference-Applied: include-unknown-enum-members

{
    "value": [
        { 
            "displayName": "My Laptop", 
            "processorArchitecture": "x64"
        },
        { 
            "displayName": "Prototype", 
            "processorArchitecture": "quantum"
        }
    ]
}

Patch Example

PATCH https://graph.microsoft.com/v1.0/deviceManagement/managedDevices/1

{ 
    "displayName": "Secret Prototype",
    "processorArchitecture": "unknownFutureValue"
}
{
    "id": "1",
    "displayName": "Secret Prototype",
    "processorArchitecture": "unknownFutureValue"
}
GET https://graph.microsoft.com/v1.0/deviceManagement/managedDevices/1
Prefer: include-unknown-enum-members
Preference-Applied: include-unknown-enum-members

{
    "id": "1",
    "displayName": "Secret Prototype",
    "processorArchitecture": "quantum"
}

Flag Enum Examples

For the following examples we will consider the windowsUniversalAppX entity which refers to the windowsArchitecture flag enum type.

<!-- Simplified entity for example purposes -->
<EntityType Name="windowsUniversalAppX" BaseType="graph.entity">
    <Property Name="displayName" Type="Edm.String" />
    <Property Name="applicableArchitectures" Type="graph.windowsArchitecture"/>
</EntityType>

When the windowsArchitecture enum was initially published to Graph it was defined as below:

<!-- Slightly modified enum for example purposes -->
<EnumType Name="windowsArchitecture" IsFlags="true">
    <Member Name="none" Value="0"/>
    <Member Name="x86" Value="1"/>
    <Member Name="x64" Value="2"/>
    <Member Name="arm" Value="4"/>
    <Member Name="neutral" Value="8"/>
    <Member Name="unknownFutureValue" Value="16" />
</EnumType>

The enum was later extended to add a new value of quantum leading to the below CSDL

<EnumType Name="windowsArchitecture" IsFlags="true">
    <Member Name="none" Value="0"/>
    <Member Name="x86" Value="1"/>
    <Member Name="x64" Value="2"/>
    <Member Name="arm" Value="4"/>
    <Member Name="neutral" Value="8"/>
    <Member Name="unknownFutureValue" Value="16" />
    <Member Name="quantum" Value="32" />
</EnumType>

Flag Enum Default Behavior

GET https://graph.microsoft.com/v1.0/deviceAppManagement/mobileApps?$select=displayName,applicableArchitectures
{
    "value": [
        { 
            "id": "0", 
            "displayName": "OneNote", 
            "applicableArchitectures" : "neutral"
        },
        { 
            "id": "1",
            "displayName": "Minecraft",
            "applicableArchitectures": "x86,x64,arm,unknownFutureValue"
        }
        { 
            "id": "2",
            "displayName": "Edge", 
            "applicableArchitectures": "x64,arm,unknownFutureValue"
        }
    ]
}

In this case the value of the applicableArchitectures property includes quantum however since the client did not request the include-unknown-enum-members header the value was replaced with unknownFutureValue

Flag Enum Include opt-in Header

GET https://graph.microsoft.com/v1.0/deviceAppManagement/mobileApps?$select=displayName,applicableArchitectures

Prefer: include-unknown-enum-members
Preference-Applied: include-unknown-enum-members

{
    "value": [
        { 
            "id": "0", 
            "displayName": "OneNote", 
            "applicableArchitectures" : "neutral"
        },
        { 
            "id": "1",
            "displayName": "Minecraft",
            "applicableArchitectures": "x86,x64,arm,quantum"
        }
        { 
            "id": "2",
            "displayName": "Edge", 
            "applicableArchitectures": "x64,arm,quantum"
        }
    ]
}

Flag Enum Default Filter Behavior

GET https://graph.microsoft.com/v1.0/deviceAppManagement/mobileApps?$select=displayName,applicableArchitectures&$filter=applicableArchitectures has unknownFutureValue
{
    "value": [
        { 
            "id": "1",
            "displayName": "Minecraft",
            "applicableArchitectures": "x86,x64,arm,unknownFutureValue"
        }
        { 
            "id": "2",
            "displayName": "Edge", 
            "applicableArchitectures": "x64,arm,unknownFutureValue"
        }
    ]
}

Flag Enum Include opt-in Header Filter Behavior

GET https://graph.microsoft.com/v1.0/deviceAppManagement/mobileApps?$select=displayName,applicableArchitectures&$filter=applicableArchitectures has unknownFutureValue

Prefer: include-unknown-enum-members
Preference-Applied: include-unknown-enum-members

{
    "value": []
}

Flag Enum Patch Example

PATCH https://graph.microsoft.com/v1.0/deviceAppManagement/mobileApps/1

{ 
    "displayName": "Minecraft 2",
    "processorArchitecture": "unknownFutureValue"
}
{
    "id": "1",
    "displayName": "Minecraft 2",
    "applicableArchitectures": "unknownFutureValue"
}
GET https://graph.microsoft.com/v1.0/deviceAppManagement/mobileApps/1

Prefer: include-unknown-enum-members
Preference-Applied: include-unknown-enum-members

{
    "id": "1",
    "displayName": "Minecraft 2",
    "applicableArchitectures": "x86,x64,arm,quantum"
}