6:56 p.m.
From the jsr-314-comments mailbox comes this discussion between myself
and
Mathias Werliz about inter-component validation. Unfortunately the
discussion progressed outside of the mailinglist, so the post below is the
aggregate of the individual messages. If there is confusion we can summarize
the discussion up to this point and continue the discussion on each
individual point.
---------- Forwarded message ----------
From: Dan Allen <dan.j.allen(a)gmail.com>
Date: Thu, Jul 9, 2009 at 2:09 PM
Subject: Re: [jsr-314-open] inter-component and form-level validation
To: "Werlitz, Mathias" <werlitz(a)adesso.de>
Cc: jsr-314-comments(a)jcp.org
On Thu, Jul 9, 2009 at 11:36 AM, Werlitz, Mathias <werlitz(a)adesso.de> wrote:
Sorry for the late response. I’m very busy on a customer project at
the
moment, analysing JSF 1.2 (view state) and Facelets memory consumption on
IBM Portal 6.1.
I agree that there are two basic approaches to solve multiple-field /
form-validation:
1. model based validation after the update model phase and
2. validating the converted values of multiple components
In both cases there should be an easy way to assign the proper validation
message to the originating input component or group of input components. With
complex forms including inputs within naming containers like <h:dataTable>
this may become quite complicated. Flattening the properties of the object
graph for JSR-303 model validation does not seem to be a good idea in this
case.
I realize that JSR-303 isn't going cover every case. I must admit to still
being the fence on how to best handle the situation you are citing...meaning
can I do it comfortably with JSR-303 or not? I think a solid use case would
help us test the limits.
Well I simplified a test case – I’m unsure that this is easily done with
JSR-303. Image a form with a master date and several additional dates. The
number of the additional dates is dynamic – will be configured by the user
(added and removed) or determined by the server.
For simplicity there is only one multi-field validation rule: all
additional dates must be after the master date. The view would look
something like this (note: the list of additional dates is a list of a
custom bean that stores the date and maybe additional data for every entry):
<h:input id=”masterDate” value=”mybean.masterDate” />
<h:datatable value=”mybean.myAdditionalDates” var=”item” >
<h:input id=”addtionalDate” value=”item.additionalDate” />
</h:datatable>
This could be done with JSR-303. You can have a validation annotation on the
array (or List) property holding the "after" dates and say that they must
come after the master date property. But again, the limitation is that it
has to happen after update model values.
Earlier when I said you have to flatted your model, I didn't mean you
couldn't use collections. You just can't easily validate a property on one
class against a property on another.
But pointing that aside, you could still accomplish w/ a regular JSF
validator if all conversions happened before the validation phase. Then you
just do something like:
<h:input id="additionalDate" value="#{item.additionalDate}">
<x:validateAfter id="masterDate"/>
</h:input>
One downside of the model based validation is that the whole validation
process is split up into two phases. That means the user may get the error
messages in two bunches: first the errors of the validation phase and later
the model errors. This can be quite confusing.
The reality is, there are two validation phases in input-based
applications. You simply cannot test some business validations if you don't
have correct data to start with. I think the real point is to make sure that
all input validation is handled together...and that business validation is
really business validation. Having one date before another I agree is likely
an input validation, not a business validation.
Yes, that’s the point. At the moment JSF does make it very hard to do the
input validation altogether.
There will likely always be two steps. The question is, can we get those two
steps right?
To emphasize why there must be two validation phases, consider this case. You
walk into an ice cream store and the employee asks you which flavor of ice
cream you want. You say you want pizza. They say, "Sir, we don't have pizza,
you have to pick and ice cream." Then you say that you want Heath ice cream.
The employee says, sorry, we don't have that in stock. So the first is an
input validation, the second is business. The employee couldn't have told
you they don't have Heath ice cream in stock because the employee doesn't
know what you want. It's not really that confusing.
I agree with you, but in fact there are three steps where messages could be
associated with an input field (convert, validation, business rules) and
every step depends on the previous one.
Well, one common requirement of our customers is: Display error messages as
early as possible. Separating the validation into two phases makes this
hard. Using good old Struts this example is no problem at all.
That's because Struts effectively updated the model and then validated,
moving all validation to the later phase. In JSF there is an understanding
that values won't get assigned to the model unless they are valid syntax or
type. You could throw that out the window and do all your validations after
the update model values phase and get the same result. So we are questioning
the fundamental guarantee of JSF (which, by the way, may need to be
questioned).
Well I think you got me wrong. The point is that in Struts you are able to
store all the form data (as strings) in a form bean. You are responsible to
make your own conversation. But because of that you are able to validate all
input data including multi-field validation. On success you proceed to
assign the values on your own to the real model.
That’s not perfect. The only problem with JSF is that you don’t have this
intermediate view on the form data where all converted values of the form is
available altogether before deciding to move on to the update model phase.
I think we are saying the same thing. JSF applies the values directly to the
model by attempting to convert each value. Now, you could copy all
properties to a model with string properties and essentially coerce JSF into
skipping validation so that you can handle it yourself, but that really
defeats a large goal of JSF.
I like your idea of dividing converting and validation. I think JSR-303
model based validation is not sufficient. In the discussion with my
college we had a similar idea as a workaround for JSF 1.2: We thought about
a special custom validator added to all relevant input components that
collects all converted input data from the components and the corresponding
client ids/component instances. This also works fine with <h:dataTable>. The
data could be collected with a Map or special validation-model bean. At the
end of the validation phase another special form/multi-field validator
(possible phase listener) is called with the collected data and invokes the
validation logic. This way you get all converted data, components/client
ids, the real model data is not touched at all and the whole validation is
processed in one phase.
It seems blatantly obvious to me that all conversion should happen before
any validation occurs. I think the current situation is ridiculous and it's
the root of why multi-field validation is so screwed up to begin with.
See my previous comment… The question is: when this will change. JSF 2.0
would be the right version. But I guess it’s already too late for such a
fundamental change in the lifecycle – separating conversation and
validation.
It won't be JSF 2.0. Hopefully JSF 2.1 or sooner.
-Dan
--
Dan Allen
Senior Software Engineer, Red Hat | Author of Seam in Action
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