T5: Troubles editing a list of objects

[lasitha]

Marcus, you mentioned offline you'd gotten this to work by setting the
Loop component's 'volatile' parameter to true.  I've scanned the
source and must admit i don't quite understand how the component is
designed to work when _not_ volatile.  If anyone's had any success
updating state within a non-volatile loop, please chime in.

I do have a couple of related suggestions:

1. If you don't use an encoder, tapestry will try to serialize the
whole list (forcing the contained type to implement Serializable).
This might be ok - particularly if you use a client storage strategy -
but i think its cleaner to use a primary key encoder and allow it to
look up the list values from your backend on every hit.  This also
ensures you don't run the risk of having two sets of objects floating
around.

I've modified your example to use an encoder and appended the code below.

You might also want to check out the ToDoList example in the
tapestry-core test source:
https://svn.apache.org/repos/asf/tapestry/tapestry5/trunk/tapestry-core/src/test
Look for: org.apache.tapestry.integration.app1.pages.ToDoList.java and
the corresponding ToDoList.html

(There's also a ToDoListVolatile variation, but its essentially your
solution with volatile="true").

2. Perhaps a Grid component is a more natural (albeit heavier) fit for
this kind of scenario?  It may not be worth it if your example doesn't
get any more complicated, but throw in some validation, add/delete use
cases and the simple list may not hold up.  I haven't used a Grid
myself, but i hear good things :)

Cheers,
lasitha

public class TestList {
    private DefaultPrimaryKeyEncoder<String, Value> encoder;
    private Value value;    // current loop variable
    private ValueRepository valueRepository = new ValueRepository();
 // would be @Inject-ed instead

    public void onPrepare() {
        encoder = new DefaultPrimaryKeyEncoder<String, Value>();
        for(Value value: valueRepository.retrieve()) {
            encoder.add(value.getName(), value);
        }
    }
    public void onSuccess() {
        repository.update(encoder.getValues());
    }
    public List<Value> getValues () {
        return encoder.getValues();
    }
    public PrimaryKeyEncoder getEncoder() {
        return encoder;
    }
    public Value getValue () {
        return this.value;
    }
    public void setValue (Value value) {
        this.value = value;
    }

    public static class Value {
        private String name;
        private String text;
        private boolean used;

        public Value(String name, String text, boolean used) {
            this.name = name;
            this.text = text;
            this.used = used;
        }
        public String getName () {
            return this.name;
        }
        public void setName (String name) {
            this.name = name;
        }
        public String getText () {
            return this.text;
        }
        public void setText (String text) {
            this.text = text;
        }
        public boolean isUsed () {
            return this.used;
        }
        public void setUsed (boolean used) {
            this.used = used;
        }
    }


    public static class ValueRepository {

        private static List<Value> values = new ArrayList<Value>() {{
            add(new Value("first", "text one", false));
            add(new Value("second", "text two", false));
            add(new Value("third", "text three", false));
        }};
        public List<Value> retrieve() {
            return values;
        }
        public void update(List<Value> values) {
            // in this case, the Value instances in the static list
have already been modified in place
            // if this were a DB backed repo, we might loop through
the values and persist 'em here
        }
    }
}


On Wed, 05 Sep 2007, Marcus Schmidke wrote:
>
> ...
>
> I'm trying to edit a list of values:
> ...
>
> The page is rendered perfectly. On Submit, the new values are passed
> into some Value objects.
>
> But: those Value objects are serialized/deserialized instances of the
> original Value objects. While the List still holds the original Value
> objects, only copies of them get modified. Result is that my program
> code (which works on the list) never sees the modified versions, and
> on re-rendering, the old values are displayed again.
>
> What am I doing wrong??
>
>
> Marcus.

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