Mailing-List: contact torque-user-help@db.apache.org; run by ezmlm
Precedence: bulk
Reply-To: "Apache Torque Users List" <torque-user@db.apache.org>
Date: Fri, 20 Jan 2006 23:24:37 -0800 (PST)
From: Thomas Fischer <tfischer@apache.org>
To: Apache Torque Users List <torque-user@db.apache.org>
Subject: AW: Joins in torque
In-Reply-To: <NJBBLABMGLOPAFMCKFKDKEGBCGAA.spiegel@szwo.de>
Message-ID: <20060120224858.D33311@minotaur.apache.org>
References: <NJBBLABMGLOPAFMCKFKDKEGBCGAA.spiegel@szwo.de>
MIME-Version: 1.0
Content-Type: MULTIPART/MIXED; BOUNDARY="0-19172825-1137828277=:33311"

--0-19172825-1137828277=:33311
Content-Type: TEXT/PLAIN; charset=X-UNKNOWN; format=flowed
Content-Transfer-Encoding: QUOTED-PRINTABLE

Hi,

I do not understand your problem. My guess is that the misunderstanding=20
arises a) because of Torque's silent db hits and caching the associated=20
objects and b) some peculiarities of the caching.
Note: All this assumes you have standard generator settings (no=20
managers etc).

regarding a) Assume you have the following code: (All this assumes you=20
have standard generator settings (no managers etc)).

Criteria criteria =3D new Criteria();
List t12s =3D T12Peer.doSelect(criteria);
T12 t12 =3D (T12) T12s.get(0);
T1 t1 =3D t12.getT1(); // will query the db. t12.t1 was not read before.
T1 othert1 =3D t12.getT1(); // Will not query db. t12.t1 Was read before.
                           // (in fact, t1 =3D=3D othert1)

And now using doSelectJoinXXX

Criteria criteria =3D new Criteria();
List t12s =3D T12Peer.doSelectJoinT1(criteria);
T12 t12 =3D (T12) T12s.get(0);
T1 t1 =3D t12.getT1(); // will NOT query the db. t12.t1 was already read
                      // by the doSelectJoin method

And finally (to complete the confusion):

Criteria criteria =3D new Criteria();
criteria.addJoin(T12Peer.T1_ID,T1Peer.T1_ID);
List t12s =3D T12Peer.doSelect(criteria);
T12 t12 =3D (T12) T12s.get(0);
T1 t1 =3D t12.getT1(); // will query the db! explanation below.

The first two examples should be clear because once you do T12.getT1()=20
the t1 result is cached in t12 and not read again. The DoSelectJoinXXX=20
method fills the t12.t1 objects by using a join.

The last example is more difficult: If you use Criteria.addJoin(), the=20
join is NOT used to fill the associated objects (in this case t12.t1). The=
=20
join can only be used to specify which t12's can be read.

regarding b) Consider the following code:
Criteria criteria =3D new Criteria();
List t12s =3D T12Peer.doSelect(criteria);
T12 t12 =3D (T12) T12s.get(0);
T1 t1 =3D t12.getT1();
List associatedT12s =3D t1.getT12s(); // will hit db! was not filled before

Even if ((T12)associatedT12s.get(0)).equals(t12) would be true, in no case=
=20
will ((T12)associatedT12s.get(0)) =3D=3D t12 will be true. Just because you=
=20
fill one "direction" of association, this does not mean the other=20
"direction" is filled automatically. Read and debug the generated source=20
code of the methods T12.getT1() and t1.getT12s() for more information.

I hope this shed some light on what is going on.

      Thomas


On Fri, 20 Jan 2006, Stephan Spiegel wrote:

> Hi,
>
> first thanks for the fast and good response.
>
> The doSelectJoinXXX methods are in the BaseT12Peer because here are the
> foreign keys pointing to T1 and T2, so I could/can do T12.doSelectJoinT1(=
)
> and T12.doSelectJoinT2(). The point is, that I do not get any other resul=
t
> then just doing a doSelect and manually bring them together as done in th=
e
> following example:
>
> (Method in T12Peer):
>
> public static List bringThemTogether () throws TorqueException {
> =09Criteria crit =3D new Criteria();
> =09List xx =3D doSelect(crit);
> =09for (int i =3D 0; i < xx.size(); i++) {
> =09=09T12 temp_obj1 =3D (T12)xx.get(i);
> =09=09T1 temp_obj2 =3D (T1)temp_obj1.getT1();
> =09=09T2 temp_obj3 =3D (T2)temp_obj1.getT2();
> =09=09HashMap h =3D new HashMap();
> =09=09h.put("Table1",temp_obj2);
> =09=09h.put("Table2",temp_obj3);}
> =09=09xx.set(i,h);
> =09}
> =09return xx;
> }
>
> using this I can directly access the relations between the values of T1 a=
nd
> T2.
>
> I can't really see an effect using the doSelectJoin methods, but may be I=
'm
> totally blind in the moment. Or does the above method hundreds of selects=
?
> (I will have a look for the log4j as mentioned of Greg)
>
> Stephan
>
> -----Urspr=FCngliche Nachricht-----
> Von: Thomas Fischer [mailto:fischer@seitenbau.net]
> Gesendet: Donnerstag, 19. Januar 2006 17:57
> An: Apache Torque Users List
> Betreff: RE: Joins in torque
>
>
>
>
>
>
> Hi,
>
> There is no built-in support at the moment to get more than one level of
> indrection read in at once.
> As far as I can see, you have 3 1/2 possibilities:
>
> 1a) read the values one after another. Assuming you have defined foreign
> keys (I'm not sure whether they should defined in T1 and T2 or in T12, on
> this depends whether the doSelectJoinXXX methods are generated in T1Peer
> and T2Peer or in T12Peer), do T1Peer.doSelectJoinT12(). For each T1Entry
> you get, fetch the corresponding T12 Entry (this is already read from the
> database) and then do T12.getT2s() (this will access the database each ti=
me
> you fetch a T2 Entry).
>
> 1b) do the same as in a1, but omit the T12.getT2s() step. Instead, get al=
l
> T2-Ids from all T12 you read in, do T2Peer.doSelect() with a criteria whe=
re
> all needed T2Ids are selected, and do the linking of the T2 objects to th=
e
> T12's manually.
>
> 2) look at the template code for generating the doSelectJoinXXX methods a=
nd
> extend them for two levels of indirection.
>
> 3) A time ago, someone proposed a class which can read a whole tree of
> objects at once. It can be found in scarab (somewhere around TRQS260). It
> is rather reflection-centric and I do not have an idea whether it works
> with Torque 3.2, but maybe that is what you want.
>
> Personally, I use a modified method 1b). I would read all T1 I want, gath=
er
> the collection of T1 ids to read the associated T12's and link them
> manually to the T1's. Then I'd use the T2 ids from there to read the T2's=
,
> and link them manually to the T12's. This is rather fast (one select per
> level of indirection, no object is transferred twice) and quite easy to
> implement. You might have to override the initCollXXX() methods for the
> used collections to make them public.
>
>    Thomas
>
>
> "Stephan Spiegel" <spiegel@szwo.de> schrieb am 19.01.2006 17:17:29:
>
>> Hi, (in case this message is double please excuse me)
>>
>> I really do not understand what to do, I do not get the expected results=
!
>>
>> Let=B4s say I have 3 Tables: T1, T2 and T1_2
>> T1:
>> ID (integer pk)
>> value (varchar)
>> ...
>>
>> T2:
>> ID (integer pk)
>> value (varchar)
>> ...
>>
>> T1_2:
>> T1_ID (integer fk->T1)
>> T2_ID (integer fk->T2)
>>
>> As a result, I would like to have a union table showing the values of T1
> and
>> T2
>> in SQL this would be: select T1.value, T2.value from T1, T2, T1_2 where
>> T1.ID =3D T1_2.T1_ID and T2.ID =3D T1_2.T2_ID
>>
>> if I get more than this (select * ...) would be fine as well.
>>
>> So, I have my classes but when I try to use them as written in Peers
> HowTo
>> (doSelectJoin...) or in Criteria HowTo (crit.addJoin(...)) I always get
> only
>> the values of the T1_2-table
>>
>> As a first step, I try just to get the first half (result should show:
>> T1.value, T1_2.T2_ID)
>> so it should correspond to:
>> doSelectJoinT1(crit) in T1_2Peer
>> or:
>> crit.addJoin(T1.ID,T1_2.T1_ID,Criteria.LEFT_JOIN)
>>
>> as a result I just get the T1_2 values. I checked the
> mailing-list-archives,
>> I can=B4t find a helpful message. Where is my mistake? Could somebody te=
ll
> me
>> exactly how to add this join?
>>
>> (I=B4m using torque-3.2, MySQL 5, defaultidMethod=3Dnative)
>>
>> thanks in advance, Stephan
>>
>>
>>
>> ---------------------------------------------------------------------
>> To unsubscribe, e-mail: torque-user-unsubscribe@db.apache.org
>> For additional commands, e-mail: torque-user-help@db.apache.org
>>
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: torque-user-unsubscribe@db.apache.org
> For additional commands, e-mail: torque-user-help@db.apache.org
>
>
>
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: torque-user-unsubscribe@db.apache.org
> For additional commands, e-mail: torque-user-help@db.apache.org
>
>

--0-19172825-1137828277=:33311
Content-Type: text/plain; charset=us-ascii

---------------------------------------------------------------------
To unsubscribe, e-mail: torque-user-unsubscribe@db.apache.org
For additional commands, e-mail: torque-user-help@db.apache.org
--0-19172825-1137828277=:33311--