[Middlegen-user] Many2Many and One2Many

[Brian Cochran]

Hey All,

When I specify many2many relationships the one2many relationships to the
mapping table are still generated and although no entity is generated, the
references to it are. For example:

A *- C -* B representing a many2many between A and B. I am using the
following

<table name="A" generate="true" />
<table name="B" generate="true" />

<many2many>
<tablea name="A" generate="true" />
<jointable name="C" generate="false" />
<tableb name="B" generate="true" />
</many2many>

I create the database with

CREATE TABLE A ( aId integer, ..., PRIMARY KEY(aId));
CREATE TABLE B ( bId integer, ..., PRIMARY KEY(bId));
CREATE TALBE C ( aId, bId, PRIMARY KEY(aId,bId),
FOREIGN KEY(aId) REFERENCES A,
FOREIGN KEY(bId) REFERENCES B );

Middlegen will not create the entity C but it will not remove the
one-to-many relation from C to A or vise-versa if the relationship is
bidirectional. What I am wondering is why, after you have found the
existance of a many2many, are the one2manys kept around. This has been
causing me problems because the relationship between (A,B) and (C) is still
generated but the entity C does not exist.

I'm looking at the last line of addMany2ManyRelationships and wondering if
we couldn't add something in there to remove the one2many we just replaced.
Let me know if I'm just missing something here.

Thanks a bunch,
Brian

[Aslak Hellesøy]

-----Original Message-----
Cochran
Sent: 18. september 2002 02:39
Subject: [Middlegen-user] Many2Many and One2Many
Hey All,
When I specify many2many relationships the one2many relationships to the
mapping table are still generated and although no entity is generated, the
A *- C -* B representing a many2many between A and B. I am using the
following
<table name="A" generate="true" />
<table name="B" generate="true" />
<many2many>
<tablea name="A" generate="true" />
<jointable name="C" generate="false" />
<tableb name="B" generate="true" />
</many2many>
I create the database with
CREATE TABLE A ( aId integer, ..., PRIMARY KEY(aId));
CREATE TABLE B ( bId integer, ..., PRIMARY KEY(bId));
CREATE TALBE C ( aId, bId, PRIMARY KEY(aId,bId),
FOREIGN KEY(aId) REFERENCES A,
FOREIGN KEY(bId) REFERENCES B );
Middlegen will not create the entity C but it will not remove the
one-to-many relation from C to A or vise-versa if the relationship is
bidirectional. What I am wondering is why, after you have found the
existance of a many2many, are the one2manys kept around. This has been

Just because an A-B is found doesn't necessarily mean A-C or B-C can be
removed. It all depends on whether C should be generated or not. The problem
was that the template didn't check for this. It does now, so if you CVS
update, it should work as expected.

If you set C to generate="false", you'll only get A-B.
If you set C to generate="true", you'll get A-B,A-C,B-C.

Thanks for reporting this issue!

Aslak

causing me problems because the relationship between (A,B) and
(C) is still
generated but the entity C does not exist.
I'm looking at the last line of addMany2ManyRelationships and wondering if
we couldn't add something in there to remove the one2many we just
replaced.
Let me know if I'm just missing something here.
Thanks a bunch,
Brian
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