As discussed above, if multiItemTypeMembershipsEnabled is true, the elements in siteIds properties can include the IDs of several different item types. This can make it difficult to retrieve the IDs of an individual item type. For example, suppose the value of a product item’s siteIds property includes siteConfiguration, storeConfiguration, siteGroup, and storeGroup IDs. If you want to retrieve just the storeConfiguration IDs, your code would need to examine all of the siteIds elements and determine which ones represent storeConfiguration items.

To make looking up individual item types more efficient, the Oracle Commerce Platform includes the atg.multisite.SiteMembershipDerivation class. You can use SiteMembershipDerivation to compute derived properties, with each property holding the IDs of an individual context membership item type. For example, you can configure the product item descriptor to use SiteMembershipDerivation to create a storeIds derived property whose value is a collection of the storeConfiguration IDs that appear in a product’s siteIds property.

Note that the derived property value includes only the storeConfiguration items that explicitly appear in the siteIds property, and does not include implicit references based on group membership. For example, if the value of siteIds is [st:store500,stg:storeGroupUS], the value of the storeIds derived property is [store500]; it does not include the ID for each store that is a member of storeGroupUS.

You can define a separate derived property for each site configuration item type and site group item type in the Site Repository. For example, if you have siteConfiguration, storeConfiguration, siteGroup, and storeGroup item types in the Site Repository, the definition for the product item in the catalog repository might include:

<item-descriptor name="product">
     ...
  <property name="webSiteIds" data-type="set" component-data-type="string"
    queryable="false" writable="false">
    <derivation user-method="atg.multisite.SiteMembershipDerivation"></derivation>
    <attribute name="itemDescriptorName" value="siteConfiguration"/>
  </property>

  <property name="storeIds" data-type="set" component-data-type="string"
    queryable="false" writable="false">
    <derivation user-method="atg.multisite.SiteMembershipDerivation"></derivation>
    <attribute name="itemDescriptorName" value="storeConfiguration"/>
  </property>

  <property name="siteGroupIds" data-type="set" component-data-type="string"
    queryable="false" writable="false">
    <derivation user-method="atg.multisite.SiteMembershipDerivation"></derivation>
    <attribute name="itemDescriptorName" value="siteGroup"/>
  </property>

  <property name="storeGroupIds" data-type="set" component-data-type="string"
    queryable="false" writable="false">
    <derivation user-method="atg.multisite.SiteMembershipDerivation"></derivation>
    <attribute name="itemDescriptorName" value="storeGroup"/>
  </property>
    ...
</item-descriptor>

Note that the derived properties must be non-queryable and read-only.