Implementing dynamic paged queries - POJOs in Action: Developing Enterprise Applications with Lightweight Frameworks - page 441

StringBuffer queryString,
Map parameters) {
PagedQueryResult result = (PagedQueryResult) getJdoTemplate()
.execute(
new ExecuteFindOrdersQuery(queryString
.toString(), pageSize, parameters));

return result;
}

}

Let's look at the details:

B

The findOrders() method calls a series of helper methods that construct a JDOQL
query from the OrderSearchCriteria and execute it.
The makeSelectFrom() method creates the initial part of the query.
The addWhere() method constructs the where clause and appends it to the query.
It has conditional logic that adds an expression to the where clause for each of the
search criteria that has been specified in the OrderSearchCriteria object. The
addWhere() method returns a map containing the query parameters, which is later
passed to Query.executeWithMap() .
The addOrderBy() method adds an order by clause to the query.
The addRange() method adds a range clause to the query.
The executeQuery() method executes the query using ExecuteFindOrdersQuery ,
which is a JdoCallback .
As you can see, we had to write a lot of code to generate a JDO query. Even if some
code is refactored into a reusable utility class, the repository would still contain
some messy conditional logic and JDOQL fragments, which makes it error-prone
and difficult to maintain. But we mostly have to tolerate this problem because of
the benefits of JDOQL .

C
D
E

F

G

11.4.2 The ExecuteFindOrdersQuery class

ExecuteFindOrdersQuery is a JdoCallback that is executed by JDOOrderRepository-
Impl . It defines a doInJdo() method, which is called by the JdoTemplate . This
method uses the Kodo JDO API s to configure the object loading and execute the
query. Here is the code: