Hi,

I’ve been experiencing this = ‘problem’ too. I currently use the left joins solution when there are <=3D3 = tables, otherwise I just query the type and perform a single join, that seems to = be faster than paying the overhead associated with the left = joins.

Niels

From: = Poitras Christian [mailto:Christian.Poitras@ircm.qc.ca]
Sent: vrijdag 23 maart = 2007 22:22
To: user-java@ibatis.apache.org
Subject: RE: Polymorphism = question

Hi.

You can always do some left joins = with the id. Something like.

Select id, col1, col2, type, colX, = colY, colZ, colW

From BaseTable LEFT JOIN = ChildTable1 ON BaseTable.id =3D ChildTable1.id LEFT JOIN ChildTable2 ON BaseTable.id = =3D ChildTable2.id

Then any resultMap for these will = work since the columns must be there if the map reads it, otherwise columns = are unnecessary.

This approch seems to be the only = thing that would work with a join.

Still, you can do a twist = with discriminator tag.

= </discriminator>

</resultMap>

</resultMap>

</resultMap>=

By making sure the subClass calls = setters of your main class, you can force a second select to be call to populate values from child table.

I doudt you can make a reference to = the populating object itself (being able to write "this" would be = a cool improvement!) inside the disciminator when you would like = a second call to database...

Possible = improvement.

</resultMap>=

Christian

From: Mikael Andersson [mailto:mail.micke@gmail.com]
Sent: Friday, 23 March = 2007 14:49
To: user-java@ibatis.apache.org
Subject: Polymorphism = question

Hi
I have a polymorphism problem which I'm not sure is solvable by a pure = iBATIS solution.

I have a fixed database model which represents a hierarchy(very = simplified):

BaseTable
| id |col1 | col2 | type |

ChildTable1
| id |colX | colY |

ChildTable2
| id |colZ | colW |

Which has an obvious object hierarchy, and "type" contains a = either 'A' or 'B' indicating which child table should be used.

The id of the base and the child is the same, and the same id can not = exists in the two child tables.

I have found information which shows how the <discriminator> = element can be used with a column indicating the object to create. Which solves half = of my problem.

The other half is something which I don't think is solvable, but figured = I'd ask just in case it is.
I need the select join statement to be modified depending on the value = of the "type" column, which table to join with. I have no idea how to = do this in iBATIS, and am currently leaning towards implementing this in = Java logic (first get the type from the base table and then execute the = correct select statement).

Any help appreciated,
Mike