Using Property References

As we saw before, when defining the value of a property, we can reference the value of one or more other properties. This section goes a bit deeper into understanding the syntax of these property references.

Property Expansion

To make editing and maintenance of Platform Blueprints easier, MyST supports property expansion when defining the value of a property. This allows us to define the value of a property based on the value of one or more other properties.

When a string of the format ${some.property} appears in a property value it will be expanded to the value of the specified property.

For example, if we have the following properties:

• oracle.base - Defines the Oracle Home directory for installing the Oracle Middleware Platform.
• oui.inventory.directory - Defines the Oracle Universal Installer (OUI) Inventory Directory

The default location for (OUI) Inventory Directory is to place this in the sub-directory oraInventory under the Oracle Home. MyST enables us to set the value of the property oui.inventory.directory to ${var.oracle.base}/oraInventory.

Referencing MyST Properties

When referencing a MyST property, in order to uniquely identify it, we need to specify the full path of the property within the Platform Blueprint or Model.

The simplest way to derive the expression to reference a property is to locate the property we wish to reference within the Property Viewer and click on the ? against the Property Name. MyST will open a popover containing the expression to reference the property as shown below.

We can use the copy to clipboard icon (outlined above) to easily copy the property expression and then paste it wherever we need to reference it.

Understand the MyST Property Path

In general, a dot notation is used to traverse the property hierarchy. For example, a.b.c would mean locate c within b within a.

Referencing a property value within a component

A component is a complex type consisting of a pre-defined collection of object types. To reference a property value within a component we used the following syntax:

[<component-property-path>].<property-key>

Where

• <component-property-path> - Is the path to the component containing the property.
• <property-key> - Is the key for the property whose value we are referencing within the component.

For example, within a Platform Blueprint or Model, we have the Middleware Settings component, to reference the version property value, we would use the expression:

${[rxr.wls.Fmw-1].version}

In this example:

• rxr.wls.Fmw-1 is the <component-property-path> as defined in the table.
• version is the <property-key>.

Referencing a child component within a parent component

Reference a child component within a parent component we use the following syntax:

<parent-component-property-path>.<component-key>

Where:

• <parent-component-property-path> - Is the path to the component containing the child component.
• <component-key> - Is the key for the component that we are referencing within the parent component.

Referencing a component within a list

A list is a complex type consisting of a list of zero, one or more components of the same type. To reference a component within a list we use the following syntax:

[<parent-component-property-path>.<list-component-type>-<component-key>]

Where

• <parent-component-property-path> - Is the path to the component containing the list.
• <list-component-type> - Is the component type held in the list
• <component-key> - Is the key for the component that we are referencing within the list.

For example, a Platform Blueprint contains a list of Products (for example Java, SOA, Service Bus, RCU) that will be installed. In this example, if we want to reference the RCU component, we would use the expression:

[rxr.def.Product-rcu]

Where

• <parent-component-property-path> is rxr.def as defined in the xxxx table.
• Product is the <list-component-type>.
• rcu is the <component-key> for the RCU product component in the list

To reference the RCU product version we would use the expression:

${[rxr.def.Product-rcu].version}

For many lists, the component key defaults to the index number of the object stored in the list. For example, a WebLogic Domain contains a list of WebLogic Clusters. In this example:

• The WebLogic Domain is the object containing the list. So <parent-component-property-path> is rxr.wls
• Cluster is the component type stored in the list.
• 1 is the component key for the first cluster, 2 the component key for the second cluster, and so on.

Thus the component property path to the second cluster in the list would be expressed as [rxr.wls.Cluster-2]. To reference the cluster name we would use the expression:
${[rxr.wls.Cluster-2].name}

Referencing a property value within a property of type map

As we mentioned earlier, a component is a complex type consisting of a pre-defined collection of object types. However, we often want to add additional properties to a component, that aren't defined in advance.

We can do this using a map. A map is a list of zero, one or more property types. The list of properties is not fixed and can be added to on the fly using the Platform Editor.

To reference a property value within amap we use the following syntax:

<paramList-property-path>.param[<property-key>]

Where

• <parent-component-property-path> - Is the path to the component containing the map
• <property-key> - Is the key for the property stored in the paramList

For example, the Oracle SOA Suite Product object contains a Configuration Parameters map, that contains a number of string properties, such as audit-level and base-port. To reference the base-port value we would use the expression:

${[rxr.def.Product-soa].param[base-port]}

Referencing a Global Variable value

MyST supports the notion of global variables. These are essentially held as a key-value map. To reference a global property value within a component we used the following syntax:

${<var>.<property-key>}

where

• <var> - Is the path to the component containing the property.
• <property-key> - Is the key for the property whose value we are referencing within the component.

For example, to reference the value of global variable install.directory, we would use the expression:

${var.install.directory}