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<p class="head">BIRT FAQ</p>
<p class="subhead">Scripting</p>
<h1>Aggregates (Totals)</h1>
<h2>Q: What aggregate operations does BIRT support?</div> </h2>
"Aggregate" is the fancy word to describe totals. BIRT suppots a wide variety
of totals: sum, running sum, average, minimum, maximum, count, count distinct,
and many more. See the
<a href="../ref/ROM_Scripting_SPEC.pdf">ROM Scripting Specification</a>
for details.
<h2>Q: Does BIRT support look-ahead (two-pass) aggregates?</div> </h2>
Look-ahead aggregates are of the form "this value as a percentage of an overall
total". For example, a customer's sales as a percentage of overall sales for a
sales rep, sales region, and so on. These are often called two-pass aggregates
becuase they require the reporting tool to make one pass over the data to compute
totals, then another pass to compute the percentages for each record.
BIRT does provide support for such totals. Just enter the calculation and BIRT
figures out the right way to compute it:
<pre class="code-block">Total.percent( row.Sales, Total.sum( row.Sales ) )
<h2>Q: Is an example of simple calculations like count,
sum, max, min?</div> </h2>
<h2>Q: Does BIRT support page totals?</div> </h2>
Some reports may want to display totals over data
displayed on a page of the report. For example, a count of employees on that
page, and sum of their salaries.
BIRT release 1.0 delivers reports as a single web page, so the question is moot
for this release. BIRT reports are paginated when printed as PDF, but BIRT uses
Apache FOP to do the formatting, and so BIRT does not have visiblity into the
That said, if there is sufficient interest, the BIRT team will consider page
totals for a future release.
<h2>Q: Can I add custom logic (scripting) to my report?</div> </h2>
Yes. BIRT uses JavaScript (also known as EcmaScript) for expressions,
business logic, and integration with application-specific Java classes.
<h2>Q: JavaScript? Does that mean my code runs in the browser?</div> </h2>
When someone hears "JavaScript" the
assumption is that JS is being used to script a browser. While browser
scripting is a key use of JS, the language itself (when separated from the
browser DOM framework) is a nice little tool that is well integrated
with Java. Our goal in using JS is that a report developer can very quickly
write business logic. JS tends to be easier to learn than Java for people
who are accustomed to Visual Basic, SQL and similar scripting solutions.
Because JS is well integrated with Java, it is easy to call from business
logic into Java classes to do more advanced tasks, or if you prefer, to write
your code using Java. Further, JS allows BIRT to support aggregate expression
such as:</p>
<pre class="code-block">sum( row.orderTotal )</pre>
<p>This summarizes the orderTotal column over all rows. This makes aggregates
look like other expressions, even though the BIRT report engine needs to
"rewrite" them.
<h2>Q: Where can I learn about JavaScript?</div> </h2>
JavaScript (also known as EcmaScript) is a popular language for browser scripting,
and a wide range of books
exist that describe JavaScript in that context. An excellent one is
<a href="">
JavaScript: the Definitive Guide</a> by David Flanagan, published by
<a href="">O'Reilly</a>. This book has two
sections: Core JavaScript and Client-Side JavaScript. Use the Core section a
general reference for the JavaScript language independent of whether it is in a
client or server. VisiBone provides a useful
<a href="">on-line reference</a>.
<h2>Q: Good, but most report developers don't like write code.</div> </h2>
In BIRT, typical tasks should require no code.
Application-specific taks should require as little code as possible;
preferably just a business expression when possible. For more complex logic,
we expect a Java application developer to either create the logic, or point
the report developer to existing Java code. The report developer then calls
into the Java code from an expression. JavaScript allows all three:</p>
<li>Simple expressions: <code>row.Price * row.Quantity</code>
<li>Business expressions: choose a salutation (Mr., Mrs., Ms., etc.)
depending on a database code, and concatenate the salutation, first name and
last name.
<li>Complex logic written in Java: Compute the recommendation rating for a
stock based on factors in the database, and proprietary stock-rating
<p>Simple tasks require no code. This includes conditional formatting (make
negative numbers red, for example), data transformations (filters, sorting,
totals), conditional display (hide certain fields for certain types of
customers), and so on.
<h1>Accessing Java Classes</h1>
<h2>Q: Can BIRT access existing Java code or objects?</div> </h2>
Yes. BIRT uses the
<a href="">Mozilla Rhino</a>
JavaScript engine which provides excellent
integration with Java. See the Mozilla Rhino
<a href="">Scripting Java</a>
article for information about how to call Java from JavaScript.
A BIRT report developer could use JavaScript to access functionality of
pre-existing Java classes that may hold significant business logic that we
would like to access within the report.
Suppose our logic is in a Java package called
We'd import it into JavaScript as follows:</p>
<pre class="code-block">importPackage( );
<p>The report's <code>initialize</code> method is the best place to put the import.
Then, we can access objects and methods as if they were JavaScript objects. let's
assume that MyClass is a class within the AppLogic package, and it provides business
logic for working with, say, customer orders:
<pre class="code-block">obj = new MyClass( );
result = obj.calculate( row.balance, row.dueDate );