The built-in inheritance capability of SQL repositories lets you easily query across a complex hierarchy of sub-types, and helps optimize performance. For example, given the previous model, the following query can return both shirt and shorts items:

get all clothing items with a shipping weight > 2 pounds

The code for this query looks like this:

 // get hold of the repository
 Repository gsa = ...;

 // get the view to use for querying "clothing" type items
 RepositoryView clothingView = gsa.getView("clothing");

 // get a query builder
 QueryBuilder qb = clothingView.getQueryBuilder();

 // build the query
 QueryExpression weightLimit = qb.createConstantQueryExpression(new Integer(2));
 QueryExpression itemWeight = qb.createPropertyQueryExpression("shippingWeight");
 Query q = qb.createComparisonQuery(itemWeight,

 // run the query
 RepositoryItem[] items = clothingView.executeQuery(q);

 // separate the shirts and shorts and do whatever with them
 for (int i=0; i<items.length; i++) {
     RepositoryItem item = items[i];

     // all clothing items have a name and a description
     logDebug("clothing: " + item.getPropertyValue("name") +
              ' ' + item.getPropertyValue("description"));

     // the ItemDescriptor defines the "type" of an item
     RepositoryItemDescriptor desc = item.getItemDescriptor();

     // now we do different things, depending on the
     // type of clothing item we have
     if (desc.getItemDescriptorName().equals("shirt") {
         // shirts have a property called "season"
         logDebug("\tshirt, season = " + item.getPropertyValue("season"));

         // do shirt-related things
     else {
         // shorts have a property called "pleated"
         logDebug("\tshirt, season = " + item.getPropertyValue("pleated"));

         // do shorts-related things

This example uses the name of the item descriptor to determine the item type. You can also look at the value of the type property declared in your template. In the example, the enumerated properties are defined with the useCodeForValue attribute set to true. As result, the query looks like this:

RepositoryItem item = items[i];

Integer itemTypeCode = (Integer)item.getPropertyValue("type");
if (itemTypeCode.intValue() == 0)
    ... shirts ...
    ... shorts ...

Choice of one approach over another is largely a matter of style. The item descriptor approach uses the actual name like shirt or shorts. The type attribute approach uses the type code stored in the clothing table: typically something like 0 or 1, as in this case.