Binding multiple values to a single immutable object

[Gareth Davis]

Hi,

This is actually a repost of a stackoverflow question that I've been
unable to get an answer for:

http://stackoverflow.com/questions/1644340/multiple-field-ognl-type-converter

My problem is that I have an immutable object that is captured in
multiple fields on the UI. The http post looks like:

    capture.id = 213
    capture.description = DescriptionText

Capture is a property of my new Value type and I have a TypeConverter
set-up and ready to convert the field 'capture'. The converter is
setup up such that it gets called if the input is:

    capture = foo

Since my value object is immutable I need to be able to construct it
with the value of  'id' and 'description'. I had the bright idea over
the weekend that the following would work:

    capture[id] = 213
    capture[description] = DescriptionText

This actually does a bit better in that my converter gets called, but
instead of being called with a map of values it gets called multiple
times once for each parameter.

The more I look at the Ognl stuff and the ParametersIntercepter the
more I've convincing my self that this is just not possible with the
framework, can anybody confirm this?

A similar problem I that I'm sure somebody must have looked at before
is having a separate input fields for day, month and year and have
them bound to a single Date instance on the action. I've been looking
for some references for this sort of thing, but haven't found the
right search term yet.

Gareth

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[Robert Graf-Waczenski]

Gareth Davis schrieb:
> The more I look at the Ognl stuff and the ParametersIntercepter the
> more I've convincing my self that this is just not possible with the
> framework, can anybody confirm this?
>  

Others may have a deeper knowledge of the framework, but i would
approach your issue differently. Since setters for your html form fields
are called independently of each other and in an unpredictable order,
you should code your action to have separate members for each of the
getters/setters and have your Date instance created properly in your
action method. Or you implement a weaker form of immutability that
allows an object to shortly exist in an non-immutable state (so you can
new it with empty members and have it being accessed directly from your
setters) and then "petrify" the object in your action method. We in our
project have invented such a pattern ten years ago and are using it ever
since without looking back :-)

Robert


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[Gareth Davis]

Thanks, their is a further complexity in my system, in that the exact type
of the Value isn't actually known at compile time it is actually a kinda
urber configurable form display, hence the desire to use a TypeConverter,
but I think you are right and a different approach is inevitable. Currently
looking at binding to a Map of strings and doing the type conversation my
self.

Thanks
Gareth

2009/11/3 Robert Graf-Waczenski <rgw@...>

> Gareth Davis schrieb:
>
>  The more I look at the Ognl stuff and the ParametersIntercepter the
>> more I've convincing my self that this is just not possible with the
>> framework, can anybody confirm this?
>>
>>
>
> Others may have a deeper knowledge of the framework, but i would approach
> your issue differently. Since setters for your html form fields are called
> independently of each other and in an unpredictable order, you should code
> your action to have separate members for each of the getters/setters and
> have your Date instance created properly in your action method. Or you
> implement a weaker form of immutability that allows an object to shortly
> exist in an non-immutable state (so you can new it with empty members and
> have it being accessed directly from your setters) and then "petrify" the
> object in your action method. We in our project have invented such a pattern
> ten years ago and are using it ever since without looking back :-)
>
> Robert
>
>
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> To unsubscribe, e-mail: user-unsubscribe@...
> For additional commands, e-mail: user-help@...
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>