Using YamlObjectModel

Using YamlObjectModel

This module is meant to be used as a base to create PowerShell classes where its derived objects can be serialised and deserialised to YAML or JSON.

It uses (and depends on) YamlDotNet through the PowerShell-Yaml module to do the conversion.

Base classes

This module contains base classes you can inherit from in your project to consistently enable the following features:

• [YOMBase]: Base class that provides custom serialisation with a Kind and its spec. It also exposes the following:

  • [string] ToYaml() method
  • [string] ToString() method
  • [string] ToJson() method
  • hidden [void] ResolveSpec([IDictionary] $definition) method
  • hidden [void] ResolveSpec([string]$kind, [IDictionary] $definition) method

• [YOMSaveable]: Base class that extends [YOMBase] to also offer:

  • SaveTo([string]$Path) method: Serialise the object to the file $Path. Once saved to a path, the object has the property SavedAtPath set to the absolute path of that file.
  • Save() method: Once the object has been saved to a file (with SaveTo()), you can re-save without specifying the destination.
  • LoadFromFile([string]$Path) method: You can load the properties of an object from a file containing the serialised object or just the properties configured as default. Once loaded from file the object has the property SavedAtPath set to the absolute path of that file, and can the methods Save() and Reload() can be used.
  • Reload() method: This will read the properties from the file and set them on the object. It's particularly useful when an object might have been changed by a human, and you want your script to pick it up while it's still running.

API Dispatcher

The API dispatcher ([YOMApiDispatcher]::DispatchSpec()) is a couple of static methods with different overrides that can take a definition (deserialised YAML or hashtable with the type name).

The principle comes from Kubernetes objects that are persisted in Yaml through its spec, and describe their type via a kind property.

kind: ClassName
spec:
  property1: value1
  property2: value2

With the following class defined in PowerShell:

using namespace System.Collections
using namespace System.Collections.Specialized
using module YamlObjectModel
using namespace YamlDotNet.Serialization

class MyTest : YOMSaveableBase
{
    [string] $Property1
    [string] $Property2

    MyTest()
    {
        # Default Ctor()
    }

    MyTest([IDictionary] $Definition)
    {
        # constructor for hashtable/Ordered Dictionary
        $this.ResolveSpec($Definition) # Common method coming from YOMBase
    }

    [string] GetString()
    {
      '{0} and {1}' -f $this.Property1,$this.Property2
    }
}

We can create an instance by calling the dispatcher like so:

[YOMApiDispatcher]::DispatchSpec(@{
    kind = MyTest
    spec = @{
        Property1 = 'thingy'
        Property2 = 'something else'
    }
})

We can also