2.2. Types

2.2.1. Creating and Modifying Instances of Types

Creating or modifying an instance of a type does not have any effect on the server side, unless the changes are explicitly sent to the server calling a service method, as described below. Changes on the server side are not automatically reflected in instances that already exist in memory.

The constructors of these classes have multiple optional arguments, one for each attribute of the type. This simplifies the creation of objects, by using nested calls to multiple constructors.

In the following example, an instance of a virtual machine is created and its attributes (cluster, template, and memory) are set:

Creating a Virtual Machine Instance with Attributes

vm = OvirtSDK4::Vm.new(
  name: 'myvm',
  cluster: OvirtSDK4::Cluster.new(
    name: 'mycluster'
  ),
  template: OvirtSDK4::Template.new(
    name: 'mytemplate'
  ),
  memory: 1073741824
)

The hashes (for example, cluster: OvirtSDK4::Cluster.new) passed to these constructors are processed recursively.

In the following example, plain hashes are used instead of explicitly calling the constructors for the Cluster and Template classes. The SDK internally converts the hashes to the required classes.

Creating a Virtual Machine Instance with Attributes Expressed as Plain Hashes

vm = OvirtSDK4::Vm.new(
  name: 'myvm',
  cluster: {
    name: 'mycluster'
  },
  template: {
    name: 'mytemplate'
  },
  memory: 1073741824
)

Using constructors in this way is recommended, but not mandatory.

In the following example, a virtual machine instance is created with no arguments in the call to the constructor. You can add the virtual machine instance’s attributes one by one, using setters, or by using a combination of setters and constructors.

Creating a Virtual Machine Instance and Adding Attributes Individually

vm = OvirtSDK4::Vm.new
vm.name = 'myvm'
vm.cluster = OvirtSDK4::Cluster.new(name: 'mycluster')
vm.template = OvirtSDK4::Template.new(name: 'mytemplate')
vm.memory = 1073741824

Attributes that are defined as lists of objects in the API specification are implemented as Ruby arrays. For example, the custom_properties attributes of the Vm type are defined as a list of objects of type CustomProperty.

Adding a List of Attributes as an Array

vm = OvirtSDK4::Vm.new(
  name: 'myvm',
  custom_properties: [
    OvirtSDK4::CustomProperty.new(...),
    OvirtSDK4::CustomProperty.new(...),
    ...
  ]
)

Attributes that are defined as enumerated values in the API are implemented as constants in a module with the same name as the enumerated type.

The following example shows how the status attribute of the Vm type is defined using the VmStatus enumerated value.

case vm.status
when OvirtSDK4::VmStatus::DOWN
  ...
when OvirtSDK4::VmStatus::IMAGE_LOCKED
  ...
end
Important

In the API specification, the values of enum types are lower case, because that is the convention for XML and JSON. In Ruby, however, the convention is to use upper case for these constants.

2.2.2. Retrieving Instance Attributes

You can retrieve instance attributes using the corresponding attribute readers.

The following example retrieves the name and memory of the virtual machine instance:

Retrieving Virtual Machine Instance Attributes

puts "vm.name: #{vm.name}"
puts "vm.memory: #{vm.memory}"
vm.custom_properties.each do |custom_property|
  ...
end

Retrieving Instance Attributes as Links

Some instance attributes are returned as links and require the follow_link method to retrieve the data. In the following example, the response to a request for a virtual machine’s attributes is formatted as XML with a link:

Retrieving Virtual Machine Attributes as a Link

<vm id="123" href="/ovirt-engine/api/vms/123">
  <name>myvm</name>
  <link rel="diskattachments" href="/ovirt-engine/api/vms/123/diskattachments/">
  ...
</vm>

The link, vm.disk_attachments, does not contain the actual disk attachments. To retrieve the data, the Connection class provides a follow_link method that uses the value of the href XML attribute to retrieve the actual data.

In the following example, follow_link enables you to go to the disk attachments, and then to each disk, to retrieve the alias:

Retrieving Virtual Machine Service

vm = vm_service.get

Using follow_link to Retrieve Disk Attachment and Disk Alias

attachments = connection.follow_link(vm.disk_attachments)
attachments.each do |attachment|
  disk = connection.follow_link(attachment.disk)
  puts "disk.alias: #{disk.alias}"
end