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Subject: Re: Storing information in a join table
From: Robert Zeigler <robert.zeigler@roxanemy.com>
In-Reply-To: <AANLkTi=+AR+0SdMPnQYfVoiUDVH-XP7W+4hccGeUu0js@mail.gmail.com>
Date: Fri, 18 Feb 2011 04:18:36 -0600
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To: user@cayenne.apache.org

You can access the intermediate object if you choose not to flatten the =
relationship.  There's nothing to prevent a join table from being =
represented as its own entity in cayenne. It can make your application a =
little more complicated, but I've done it before when the join table =
carries additional meaningful information, eg, information that somehow =
modulates the join (eg: creating a createDate column on the join table =
for keeping track of exactly when the association was created... stuff =
like that).

Cheers,

Robert
On Feb 18, 2011, at 2/184:10 AM , Christian Grobmeier wrote:

>> What semantically is "isFresh" attribute? Is it a some business logic
>> attibute, or simple "autoset" variable, like timestamp etc.?
>=20
> No its business logic. In fact it defines the view-rights for the
> specific apples to the plums :-)
>=20
>> If former, you cannot live without ApplePlum ObjEntity. Is the =
problem
>> then in just setting its default value? Then you can simply set it at
>> database level.
>=20
> OK, I will try to change my mind on this one. I have hoped I could
> somehow access the intermediate object.
>=20
> THanks!
>=20
> Cheers
> Christian
>=20
>=20
>> If the default value is dynamic, like timestamp, you can try =
intercept
>> Cayenne's generating of queries:
>> http://cayenne.apache.org/doc30/custom-batchquerybuilder-factory.html
>>=20
>> 2011/2/18 Christian Grobmeier <grobmeier@gmail.com>:
>>> Hello,
>>>=20
>>> I have the following scenario:
>>>=20
>>> Apple 1 -> n ApplePlum n : 1 Plum
>>>=20
>>> I want store an additional flag in ApplePlum (lets say isFresh =3D =
true/false
>>>=20
>>> How can I do this? I know I should not use flattened relations, but
>>> they are so nice, I would like to keep them. At least it would lead =
to
>>> the Method getApplePlum->getPlum which is not very neat.
>>>=20
>>> In order to do so I have thought I could create a custom method in =
my
>>> Apple class, which copies some code from the _Apple class.
>>>=20
>>> Like this:
>>>=20
>>> public void addToAppleAsFreshPlum(Plum value) {
>>>        String relName =3D "ApplePlum";
>>>        if (value =3D=3D null) {
>>>            throw new NullPointerException("Attempt to add null =
target
>>> DataObject.");
>>>        }
>>>=20
>>>        willConnect(relName, value);
>>>        Object holder =3D readProperty("ApplePlum");
>>>=20
>>> // Now I would like to get the object created by the holder:
>>>        ((ApplePlum)holder).setFresh(true);
>>>=20
>>>        getObjectContext().propertyChanged(this, relName, null, =
value);
>>>=20
>>>        if (holder instanceof Collection) {
>>>            ((Collection<Object>) holder).add(value);
>>>        }
>>>        else if (holder instanceof Map) {
>>>            ((Map<Object, Object>) holder).put(getMapKey(relName,
>>> value), value);
>>>        }
>>>=20
>>>        setReverseRelationship(relName, value);
>>>    }
>>>=20
>>> Of course this does not work. I wonder if there is another option =
for
>>> me? Any ideas?
>>>=20
>>> Thanks in advance
>>> Christian
>>>=20
>>=20
>>=20
>>=20
>> --
>> Andrey
>>=20
>=20
>=20
>=20
> --=20
> http://www.grobmeier.de