Database query in toplink

Question

hi all,
I need to fetch single row from table and have to print it on JSF page in outputText and inputputText boxes....
what should be the procedure???
how to write the query?
and the resultset that is retrieved is in the form of vector how to put their values in outputText boxes?

Answer 1

Hello,
Your questions are pretty broad, but let me address the TopLink aspects of your questions. Once you have an object retrieved via TopLink, then you can consider your JSF presentation of the data that is housed within the object.
Lets say you have a java class named X, and you want instances of X persisted to a table that is also named X. Now you are interested in using TopLink to hydrate an instance of X so that you can render some information for that instance, which contains of course data from table X.
In general, you TopLink map X.class to the table named X with all of the columns in the table mapped to instance attributes defined on X.java or one of its superclasses.
Now the question is how to locate the row of interest from table X? Since you are interested in only one row, it is most likely that you are interested in identifying that row of interest by its primary key, which is likely some numeric surrogate key.
Lets assume you are interested in retrieval by primary key. Lets also assume that the X_ID column on the X table is its primary key. Lets also assume the id instance attribute on X.java (or from one of its superclasses) is TopLink mapped and is simply a direct to field mapping, so the id instance attribute on X.java would take on the value housed in X.X_ID. Lets further assume you want to find the instance of X where X_ID = 123.
The resultset that is retrieved via TopLink does not have to be a Vector (List) of objects. You can express to TopLink that you are only interested in retrieving one object by use of oracle.toplink.queryframework.ReadObjectQuery or oracle.toplink.sessions.Session.readObject().
If you choose the Session.readObject() approach, here is how you obtain the reference to the instance of X that represents the row where X.X_ID = 123:
obtain reference to Session via SessionManager.getManager().getSession(sessionName);
ExpressionBuilder builder = new ExpressionBuilder();
Expression selectionCriteria = builder.get("id").equal(123);
X foundInstance = (X) session.readObject(X.class,selectionCriteria);
If you choose the ReadObjectQuery approach, here is how you obtain the reference:
ReadObjectQuery query = new ReadObjectQuery();
query.setReferenceClass(X.class);
query.setSelectionCriteria(selectionCriteria); // defined above
X foundInstance = (X) session.executeQuery(query);
Once you have a handle to the X instance of interest, you can then go about rendering information about it to an end user via a JSP or JSF JSP page. Typically the queries that I show above are written as part of the implementation of an operation on a Session EJB, but it can be done without a Session EJB as well.
I suggest you take a look at the TopLink Developer's Guide : http://download-west.oracle.com/docs/cd/B31017_01/web.1013/b28218/toc.htm as well as the TopLink API Reference from Javadoc : http://download-west.oracle.com/docs/cd/B31017_01/web.1013/b28219/index.html. Both of these documents are for TopLink 10.1.3.1, but you probably want to find the documentation for the version of TopLink you are using just in case.
Hope that helps,
Doug