Join Support
Query joins are used for associating data contained in separate tables. Joins can be accomplished by using the PersistenceManager navigate methods or through adhoc WhereExpressions. The QuerySpec class also provides explicit support for appending a join to a query using link classes and roles defined in the Rose model. This offers the flexibility of the QuerySpec along with the simplicity of specifying query joins using model information. The following QuerySpec methods can be used.
appendJoin(int a_linkIndex, String a_role, Persistable a_source)
appendJoin(int a_linkIndex, String a_role, int a_targetIndex)
The following example builds a query that joins together the SubFolder and Part classes via the FolderMembership link. The query returns all folders and all of the associated parts that are contained in the folder. The following code constructs the query specification. The first section adds the classes and the attributes that should be returned. The final two lines of code join together the classes using the modeled roles for the FolderMembership link class.
QuerySpec query = new QuerySpec();
int folderIndex = query.appendClassList(wt.folder.SubFolder.class,
false);
int linkIndex = query.appendClassList(wt.folder.FolderMembership.class,
false);
int partIndex = query.appendClassList(wt.part.WTPart.class, false);
query.appendSelect(new ClassAttribute(wt.folder.SubFolder.class,
wt.folder.SubF
older.NAME),
new int[] { folderIndex } , false);
query.appendSelect(new ClassAttribute(wt.part.WTPart.class,
wt.part.WTPart.NAME),
new int[] { partIndex }, false);
query.appendJoin(linkIndex, wt.folder.FolderMembership.FOLDER_ROLE,
folderIndex);
query.appendJoin(linkIndex, wt.folder.FolderMembership.MEMBER_ROLE,
partIndex);