Implementing Ratings Type Selection and Value Transformation

Liferay DXP has three different mechanisms for rating content: Stars, Thumbs Up/Down, and Likes. Prior to 7.0, there was no way for administrators to select a ratings type as it was hard-coded. Now, portal and site admins can select the ratings type for portlet entities through the Control Panel and Site Administration. Portal admins can select default values for the ratings type while site admins can override values for their sites. All Liferay portlets take advantage of this feature, and so can custom portlets.

A custom portlet that uses ratings must define its ratings type through an OSGi component that implements the PortletRatingsDefinition interface. This class declares the usage of ratings (specifying the portlet and the entity) and the default ratings type (that can be overridden by portal and site admins). Developers can include their portlet entities in this section by defining the ratings type for the entities using OSGi modules.

The ratings values are stored in the database as normalized values to be able to easily switch among different ratings types. When the administrators change the ratings type for an entity, Liferay does a best match of the previous ratings values to values for the new ratings type. For example, when changing from Thumbs Up/Down to Likes, Portal considers all the Thumbs Up values as if they are Likes and omits all Thumbs Down values. Also, when changing from Stars to Thumbs Up/Down Portal considers ratings with 3, 4, or 5 Stars as Thumbs Up and ratings with 1 or 2 Stars as Thumbs Down.

However, there are some cases where this may not be enough or where you want to apply different or complex criteria to determine the new ratings values. Liferay provides a mechanism to allow developers to transform the ratings values as needed when admins change the ratings type. Keep in mind, this is not an interpretation of the data, this is modification of the stored ratings values. Third party developers can define their own transformations by creating an OSGi component that implements the RatingsDataTransformer interface. The highest OSGi ranking implementation is used.

Liferay by default doesn’t provide any RatingsDataTransformer implementation; the ratings values always remain the same while Liferay interprets existing values for the selected ratings type.

Specifying an Entity’s Ratings Type

Ratings type definitions needs to implement the PortletRatingsDefinition interface. The implementation of method getDefaultRatingsType returns the entity’s default ratings type. Note, it can be overridden by portal and site admins. The implementation of method getPortletId returns the portlet ID of the main portlet that uses the entity.

Implementations of PortletRatingsDefinition need to be registered in OSGi to be used by the portal. You do this in the implementation by specifying the OSGi annotation @Component with an attribute set to the name or names of the classes to use the ratings definition.

Here is an example of a PortletRatingsDefition implementation for the Blogs portlet that defines the blogsEntry ratings data:

    property = {
public class BlogsPortletRatingsDefinition implements PortletRatingsDefinition {

    public RatingsType getDefaultRatingsType() {
        return RatingsType.THUMBS;

    public String getPortletId() {
        return PortletKeys.BLOGS;


Next, let’s examine how to transform values between ratings types.

Transforming Ratings Values Between Ratings Types

If the site admin or portal admin changes the ratings type and there are existing ratings values in the database, Liferay doesn’t modify any of them. It interprets the values using the selected ratings type according to the following mechanism:

  1. When changing from Stars to …

    • Like: 1 or 2 Stars aren’t considered. 3, 4, or 5 Stars is considered a Like.
    • Thumbs Up/Down: 1 or 2 Stars are considered a Thumbs Down. 3, 4, or 5 Stars is considered a Thumbs Up.
  2. When changing from Thumbs Up/Down to …

    • Like: A Like is considered a Thumbs Up.
    • Stars: A Thumbs Down is considered 1 Star. A Thumbs Up is considered 5 Stars.
  3. When changing from Like to …

    • Stars: A Like is considered 5 Stars.
    • Thumbs Up/Down: A Like is considered a Thumbs Up.

There may be cases where this interpretation is insufficient for you or where a different criteria or algorithm needs to be applied. For these cases, Liferay provides a mechanism to allow transforming the existing ratings values. Keep in mind that this modifies the values stored in the database. Since these changes may not be reversible, you must be careful. Developers will need to create an OSGi component that implements the RatingsDataTransformer interface.

The implementation of method transformRatingsData performs the data transformation. In order to obtain a fine-grained behaviour, the framework provides the methods fromRatingsType and toRatingsType. The developer can implement them to transform data as needed, and perform different transformations for different circumstances.

This is an example of a RatingsDataTransformer that resets the score from the ratings type when passing from LIKE to STARS. In this particular case, changes are not reversible.

public class DummieRatingsDataTransformer implements RatingsDataTransformer {
    public ActionableDynamicQuery.PerformActionMethod transformRatingsData(
            final RatingsType fromRatingsType, final RatingsType toRatingsType)
        throws PortalException {

        return new ActionableDynamicQuery.PerformActionMethod() {

            public void performAction(Object object)
                throws PortalException {

                if (fromRatingsType.getValue().equals(RatingsType.LIKE) &&
                    toRatingsType.getValue().equals(RatingsType.STARS)) {

                    RatingsEntry ratingsEntry = (RatingsEntry) object;




Once you’ve implemented ratings type selection and value type transformation for your app’s entities, you can configure the default ratings type values through the Control Panel by going to ConfigurationInstance Settings and selecting the Social tab. To override the default values for a site, go to Site Administration → ConfigurationSite Settings and select the Social tab.

In this tutorial, you have learned how to set a ratings type for an entity and how to implement a ratings data transformer. Liferay salutes you with a Thumbs Up!

Rating Assets

Adding Comments to Your App

« Rating AssetsFlagging Inappropriate Asset Content »
Was this article helpful?
0 out of 0 found this helpful