Handling of default values

I got diffing objects working well so far, but there is one problem: Several properties in Kubernetes objects are scalars with default values. For example:

• int ProbeV1.FailureThreshold defaults to 3
• string ServicePortV1.Protocol defaults to "TCP" and many more. These properties are often not declared in YAML configuration. But when deserializing the YAML, the properties get the C# type default value, instead of the server default value. I.e. FailureThreshold is always 0, Protocol is always null. When diffing against the server, this will then generate a patch that sets these values to the C# default value (0/null).

How should we handle this?

• When diffing, check if the new value is the C# default value, and exclude it from the patch. This would make it impossible to actually set a field to 0 or null. Does the API have fields anywhere that can be set to the C#/Go default value? E.g. for FailureThreshold the minimum is 1, and in other places where 0 is valid I saw them use nullable/pointer types, e.g. ConfigMapVolumeSource.DefaultMode. But there are a lot of booleans that are not nullable, and this would make it impossible to switch a boolean back to false after it was set to true on the server.
• Apply the server defaults client side. This would break if they ever change the default. The defaults are only exposed through documentation, not in the schema.
• Make everything nullable. This would be a bad experience when querying from the server as these are always defined.
• Use Dictionaries or dynamic instead of strongly typed objects for deserialisation. I would like to avoid this because then we lose the formatting and autocompletion in PowerShell, and it becomes way harder to look up the merge strategies to use for properties…

[felixfbecker]

I implemented serialising into PSObject and diffing PSObject and it works well. I am setting type names so output formatting is preserved. I think this is the best approach, so we can abandon the tracked models.

> Get-Content -Raw ./deploy_orig.yml | ConvertFrom-KubeYaml | Get-Member


   TypeName: KubeClient.Models.DeploymentV1Beta1

Name        MemberType     Definition
----        ----------     ----------
Equals      Method         bool Equals(System.Object obj)
GetHashCode Method         int GetHashCode()
GetType     Method         type GetType()
ToString    Method         string ToString()
ApiVersion  NoteProperty   string ApiVersion=apps/v1beta1
Kind        NoteProperty   string Kind=Deployment
Metadata    NoteProperty   KubeClient.Models.ObjectMetaV1 Metadata=@{Annotations=System.Collections.Generic.Dictionary`2[System.String,System.Object]; Name=sourcegraph-frontend; Namespace=prod}
Spec        NoteProperty   KubeClient.Models.DeploymentSpecV1Beta1 Spec=@{MinReadySeconds=10; Replicas=3; RevisionHistoryLimit=10; Strategy=; Template=}

[felixfbecker]

Sorry, separation of concerns. I.e. not have one cmdlet that is solely responsible for parsing, diffing and querying the server. Because there may be use cases that we are not thinking of where one wants to intercept these steps.