Simone Gianni wrote: > Hi all, > what about calculated fields? In a cocoon form I have a repeater, in > the repeater there are some numeric fields, and i need to show the sum > of values in these fields at the bottom of the page. This can be done > with fd:value-changed and some javascript or custom classes, but > actually since they are mentioned on Jira in the roadmap ( > http://issues.apache.org/jira/browse/COCOON-941 ), I need them, and > they are a good idea, I was wandering how to implement them. > > I tried prototyping something, and basically arrived to this : > > .. inside the repeater .. > > <fd:field id="items" required="true"> > <fd:label>Items</fd:label> > <fd:datatype base="integer"/> > </fd:field> > <fd:field id="price" required="true"> > <fd:label>Price</fd:label> > <fd:datatype base="double"/> > </fd:field> > > <fd:calculatedfield id="subtotal" required="true" state="output"> > <fd:label>Sub total</fd:label> > <fd:datatype base="double"> > <fd:convertor type="formatting" variant="currency"/> > </fd:datatype> > <fd:algorithm type="arithmetic" operation="multiplicate"> > <fd:triggers>items,price</fd:triggers> > </fd:algorithm> > </fd:calculatedfield> > > .... outside the repeater ... > > <fd:calculatedfield id="totalitems" state="output" required="true"> > <fd:label>Total items</fd:label> > <fd:datatype base="integer"/> > <fd:algorithm type="arithmetic" operation="sum"> > <fd:triggers>/articles/*/items</fd:triggers> > </fd:algorithm> > </fd:calculatedfield> > > <fd:calculatedfield id="totalitemscost" state="output" required="true"> > <fd:label>Total cost</fd:label> > <fd:datatype base="double"> > <fd:convertor type="formatting" variant="currency"/> > </fd:datatype> > <fd:algorithm type="arithmetic" operation="sum"> > <fd:triggers>/articles/*/subtotal</fd:triggers> > </fd:algorithm> > </fd:calculatedfield> > > CalculatedField is a subclass of Field, that gets an Algortihm. The > Algorithm is a simple interface, responsible for calculating the value > and return a list of triggers. Triggers are widgets that will trigger > the re-calculation. > > Calculated fields add value change listeners on all triggers to know > when a recalculation is needed, and also to make it update gracefully > in ajax. Using triggers you don't have to disseminate the form with > value changed listeners to trigger recalculations, and also for simple > algorithms (like the arithmetic one I implemented) triggers are the > operands on which it operates. This IMMO minimizes mistakes. > > My calculated field prototype calls algorithm.calculate() in > readFromRequest(). Is there a better place?
There's a problem to compute the initial value, as trigger widgets may not be initialized (or a calculated-field's initialize() can call initialize() on the widgets it depends on). >From there on, you should only react to change events from trigger widgets. > I'm also trying to make them editable (if editable="true" specified in > the definition), so that if the user wants to "fine tune" the result > of a calculation he can modify the calculated value. Obviously, once > the calculated field has been modified by the user it will behave like > a common field, maybe until the user erases the value bringing the > field back to it's calculated nature? Yikes! Heavy FS smell! > I tried something to make them also client side, but I don't think > it's a good idea. With such a good AJAX support, client side support > is rarely useful. Also, it poses a lot of limitations and a lot more > work on it : all algorithms should be able to generate a client side > counterpart, triggers should be rendered as client side calls to > "calculateXXX" functions. There is no tidy way to do this, and some > algorithms would be very difficult to port client side. Also, on > client side there is no way of apply proper field formatting, so every > form using calculated fields with a format different from plain will > end up being a mess. > > WDYT? This adds more complexity to CForms. But if people consider it useful, well, why not. Sylvain -- Sylvain Wallez http://bluxte.net Apache Software Foundation Member
