Retrieving a value from the global cache by using a Mapping node

You can use a Mapping node to retrieve a value from a map in an embedded cache or a WebSphere® eXtreme Scale grid.

1. Open the graphical data map in the Graphical Data Mapping editor.
2. In the toolbar, click the Cache Get icon () to add a Cache Get transform to the canvas.
   When you add a Cache Get transform, you automatically add a Cache Return transform.
3. Provide values for the parameters in the Cache Put transform by completing one of the following steps:
   • Map the input elements to the Cache Get transform.
   • Identify fixed values or user-defined properties to assign to the parameters.
   Note: You can also map elements from the input tree to the Cache Return transform and use these elements to transform the returned cache value.
4. Optional: Map the Cache Return transform to the output element that you want to receive the value that is associated with the key in the key-value pair.
   Note: You can also select the elements before you click the Cache Get icon. The elements that you select in the input tree are then automatically mapped to the Cache Get transform, and the Cache Return transform is mapped to the elements that you select in the output tree.

   For example, in the following image, the Key element is mapped to the Cache Get transform, and the Cache Return transform is mapped to the Value element.

   

5. Double-click the Cache Get transform to edit the nested map.
   Note: To edit the nested map, you can also perform any of the following operations:

   • Click the Cache Get link in the Cache Get transform.
   • Click the arrow in the upper right corner of the Cache Get transform.
   • Place the mouse over the Cache Get transform, and click Click here in the pop-up window.

   The output elements of the nested map are the predefined parameters that are required to perform the Cache Get transform. If you mapped elements to the Cache Get transform, the elements are displayed as input elements in the nested map.

6. Required: Provide a value for the Key parameter of the Cache Get transform by using one of the following options:
   Note: The Cache Get transform is marked with an error until a value is provided for the Key parameter.

   • Map an element from the input tree.
   • Set a fixed value for the key by right-clicking the Key parameter in the Cache Get transform, clicking Add Assign, and adding the required value in the Properties pane. For more information about the Assign transform, see Assign.
   • Set a value for the key by using a user-defined property; see Accessing user-defined properties from a Mapping node.

   For example, in the following image, the content for the Key parameter is provided by mapping an element that is named Key from the input tree.

   

7. Optional: Map or assign values to the MapName, or CacheName and MapName parameters; for information about valid values for these parameters, see Cache Get.
8. Navigate out of the Cache Get transform by clicking the arrow icon ().
9. Double-click the Cache Return transform to edit the nested map and process the returned value.
   If you mapped the Cache Return transform to an element from the output tree, the element is displayed in the nested map.
10. Optional: Map the Value element in the Cache Return to an element in the output tree.

    The predefined Value input element in the Cache Return nested mapping has a default schema type of xs:anySimpleType. If you know the type of the Java™ object in the cache, you can map directly to a target element that has the schema type that matches the Java Object type; see Schema types that are returned for each supported Java Object type.

    If the entry in the cache might have one of several Java Object types, you can apply mapping casts to the predefined Value input element. For more information, see Cache Return.

    For example, in the following image, the Value element in the Cache Return transform is mapped to the element that is named Value in the output tree.

    

11. Optional: Right-click the Cache Get transform and select Cache > Failure to implement a nested mapping that is called if the Cache Get transform fails. For more information, see Handling global cache exceptions in a graphical data map.
    Note: You can also add a Cache Failure transform by placing the mouse over the Cache Get transform and selecting the Cache Failure icon ().
12. Save the graphical data map.