Relating Assets

Relating assets connects individual pieces of content across your site or portal. This helps users discover related content, particularly when there’s an abundance of other available content. For example, assets related to a web content article appear alongside that entry in the Asset Publisher application.

Figure 1: You and your users can find it helpful to relate assets to entities, such as this blogs entry.

Now you’ll learn how to provide a way for authors to relate content. This tutorial assumes that you’ve Adding, Updating, and Deleting Assets your application. If you’ve already done this, go ahead and begin relating your assets!

Relating Assets in the Service Layer

First, you must make some modifications to your portlet’s service layer. You must implement persisting your entity’s asset relationships.

In your portlet’s service.xml, put the following line of code below any finder method elements and then run Service Builder:
```
<reference package-path="com.liferay.portlet.asset" entity="AssetLink" />
```
Modify the add-, delete-, and update- methods in your -LocalServiceImpl to persist the asset relationships. You’ll use your -LocalServiceImpl’s assetLinkLocalService instance variable to execute persistence actions.

For example, consider the Wiki application. When you update wiki assets and statuses, both methods utilize the updateLinks via your instance variable assetLinkLocalService. Here’s the updateLinks invocation in the Wiki application’s WikiPageLocalServiceImpl.updateStatus(...) method:
```
assetLinkLocalService.updateLinks(
    userId, assetEntry.getEntryId(), assetLinkEntryIds,
    AssetLinkConstants.TYPE_RELATED);
```
To call the updateLinks method, you must pass in the current user’s ID, the asset entry’s ID, the asset link entries’ IDs, and the link type. Invoke this method after creating the asset entry. If you assign to an AssetEntry variable (e.g., one called assetEntry) the value returned from invoking assetEntryLocalService.updateEntry, you can get the asset entry’s ID for updating its asset links. Lastly, in order to specify the link type parameter, make sure to import com.liferay.portlet.asset.model.AssetLinkConstants.
In your -LocalServiceImpl class’ delete- method, you must delete the asset’s relationships before deleting the asset. For example, you could delete your existing asset link relationships by using the following code:
```
AssetEntry assetEntry = assetEntryLocalService.fetchEntry(
    ENTITY.class.getName(), ENTITYId);

assetLinkLocalService.deleteLinks(assetEntry.getEntryId());
```

Make sure to replace the ENTITY place holders for your custom -delete method.

Super! Now your portlet’s service layer can handle related assets. Even so, there’s still nothing in your portlet’s UI that lets your users relate assets. You’ll take care of that in the next step.

Relating Assets in the UI

The UI for linking assets should be in the JSP where users create and edit your entity. This way only content creators can relate other assets to the entity. Related assets are implemented in the JSP by using the Liferay UI tag liferay-ui:input-asset-links inside a collapsible panel. This code is placed inside the aui:fieldset tags of the JSP.

Add the liferay-ui:input-asset-links tag to your form. Here’s how it’s added in the Blogs application:
```
<aui:fieldset collapsed="<%= true %>" collapsible="<%= true %>" label="related-assets">
    <liferay-ui:input-asset-links
        className="<%= BlogsEntry.class.getName() %>"
        classPK="<%= entryId %>"
    />
```
The following screenshot shows the Related Assets menu for an application. Note that it is contained in a collapsible panel titled Related Assets.

Figure 2: Your portlet's entity is now available in the Related Assets *Select* menu.
Unfortunately, the Related Assets menu shows your entity’s fully qualified class name. To replace it with a simplified name for your entity, add a language key with the fully qualified class name for the key and the name you want for the value. Put the language key in file docroot/WEB-INF/src/content/Language.properties in your portlet. You can refer to the Overriding Language Keys tutorial for more documentation on using language properties.

Upon redeploying your portlet, the value you assigned to the fully qualified class name in your Language.properties file shows in the Related Assets menu.

Awesome! Now content creators and editors can relate the assets of your application. The next thing you need to do is reveal any such related assets to the rest of your application’s users. After all, you don’t want to give everyone edit access just so they can view related assets!

You can show related assets in your application’s view of that entity or, if you’ve implemented asset rendering for your custom entity, you can show related assets in the full content view of your entity for users to view in an Asset Publisher portlet.

You must get the AssetEntry object associated with your entity:

<%
long insultId = ParamUtil.getLong(renderRequest, "insultId");
Insult ins = InsultLocalServiceUtil.getInsult(insultId);
AssetEntry assetEntry = AssetEntryLocalServiceUtil.getEntry(Insult.class.getName(), ins.getInsultId());
%>

Use the liferay-ui:asset-links tag to show the entity’s related assets. For this tag, you should retrieve the entity’s class name and the variable holding your instance object, so you can return its ID. The example code below uses the example entity class Insult and an instance object variable called ins:
```
<liferay-ui:asset-links
    assetEntryId="<%=(assetEntry != null) ? assetEntry.getEntryId() : 0%>"
    className="<%=Insult.class.getName()%>"
    classPK="<%=ins.getInsultId()%>" />
```

Great! Now you have the JSP that lets your users view related assets. Related assets, if you’ve created any yet, should be visible near the bottom of the page.

Excellent! Now you know how to implement related assets in your apps.

Adding, Updating, and Deleting Assets

What is Service Builder?

Defining Content Relationships

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