On Mon, 22 Oct 2001, Max M wrote:

So, how do YOU guys do many-to-many in Zope ?

In a relational DB and using ZSQL Methods to retrieve data. -- Joel BURTON | joel@joelburton.com | joelburton.com | aim: wjoelburton Independent Knowledge Management Consultant

I just completed a similar project linking 2 Zclasses to cross-reference each other. I would like to see another reply to your Q to soft-link zclass instances rather than using a programmatic list.

But if someone renames, deletes or moves a subject I am f.*?d Or the student is. The relation to the subject is invalidated.

Allow someone to rename the "title" property, but not change the ID of the Zclass instance (lock the ID once it is created, so users cant rename it). This will retain link integrity. If they delete the instance, then there is no relationship to maintain anyway, so who cares, or create a Subject "status" property to throw up an exception to notate that the Subject is in "delete" status without deleteding the instance. -Trevor

-----Original Message----- From: zope-admin@zope.org [mailto:zope-admin@zope.org]On Behalf Of Max M Sent: Monday, October 22, 2001 3:44 PM To: Zope@Zope. Org Subject: [Zope] [ADVANCED] How do YOU guys do many-to-many in Zope without relational?

I am in the situation where I have to do what corresponds to a many-to-many relation in Zope.

I basically have two zClassses. students and subjects. There can be many subjects, and in any subject there can be any number of students.

What I do now is having a studentlist under each subject. But this doesn't really work because any single student can belong to any number of subjects.

So if this was an ordinary relational db it would be many to many.

Now I considder making a global student list and then do a recursive search for subjects in the site, so that each student can be related to a subject with a selectbox or somesuch.

But if someone renames, deletes or moves a subject I am f.*?d Or the student is. The relation to the subject is invalidated.

I have never seen it used, but would it be possible to store the "global object id" in a list in a user object, and then get the path to the subject object from that?

Or should I make the subject a global list to? That way I only have to check if the object exists or not. Not where it is in the object hierachy.

This sort of defeats the purpose of Zope's tree like structure. Doesn't it?

So, how do YOU guys do many-to-many in Zope ?

regards Max M

Max M. W. Rasmussen, Denmark. New Media Director private: maxmcorp@worldonline.dk work: maxm@normik.dk ----------------------------------------------------- Shipping software is an unnatural act

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On Monday 22 October 2001 03:44 pm, Max M allegedly wrote:

I am in the situation where I have to do what corresponds to a many-to-many relation in Zope.

I basically have two zClassses. students and subjects. There can be many subjects, and in any subject there can be any number of students.

What I do now is having a studentlist under each subject. But this doesn't really work because any single student can belong to any number of subjects.

So if this was an ordinary relational db it would be many to many.

Now I considder making a global student list and then do a recursive search for subjects in the site, so that each student can be related to a subject with a selectbox or somesuch.

But if someone renames, deletes or moves a subject I am f.*?d Or the student is. The relation to the subject is invalidated.

I have never seen it used, but would it be possible to store the "global object id" in a list in a user object, and then get the path to the subject object from that?

Or should I make the subject a global list to? That way I only have to check if the object exists or not. Not where it is in the object hierachy.

This sort of defeats the purpose of Zope's tree like structure. Doesn't it?

So, how do YOU guys do many-to-many in Zope ?

regards Max M

They way to do this is to create a lines property in the student and store the ids of the related subjects there. You use a ZCatalog and a keyword index on this property to quickly find which students belong to which subject. Now, this won't fix the renaming issue (although it does fix relocating, assuming the ids are otherwise unique), but you could get around that two ways: 1. Don't rename! Treat the id as the primary key of the subject. 2. Assign another fixed key as a property (or general attribute) of the subject for use as the unique identifier and don't ever change it for the life of the object. You will need to use a ZCatalog to make lookups on this id efficient, but this would allow you to put the object anywhere you like, and rename them without screwing up the relationships. Only deletion would break it. hth, /---------------------------------------------------\ Casey Duncan, Sr. Web Developer National Legal Aid and Defender Association c.duncan@nlada.org \---------------------------------------------------/

* Max M <maxmcorp@worldonline.dk> [011022 20:44]:

I basically have two zClassses. students and subjects. There can be many subjects, and in any subject there can be any number of students.

What I do now is having a studentlist under each subject. But this doesn't really work because any single student can belong to any number of subjects.

So if this was an ordinary relational db it would be many to many.

So, how do YOU guys do many-to-many in Zope ?

This is what the ZCatalog is for: For example, have a property for students which is a list of subject ids. This makes it easy to list subjects by students. Now if you make this property be an index on the ZCatalog, you can easily retrieve all students by subject, too. hth seb

Hi Max, I have a third ZClass, "Enrollment" which has two properties: student_id and class_id. Now you can write a method: getStudentIdsForClass(class_id) or getClassIdsForStudent(student_Id). With ZPatterns you can easily map these methods on to "listish" properties of the Students/Classes. -steve On Monday, October 22, 2001, at 02:44 PM, Max M wrote:

I am in the situation where I have to do what corresponds to a many-to-many relation in Zope.

I basically have two zClassses. students and subjects. There can be many subjects, and in any subject there can be any number of students.

On Mon, 22 Oct 2001, Max M wrote:

I basically have two zClassses. students and subjects. There can be many subjects, and in any subject there can be any number of students. .......

in such a case I will do it that way : each student_object will have a unique id, say "stu_01234" each subject_object will have a unique id, say "suj_56789" each student_object will have a list of subjects were he applied : ['suj_56789','suj_567','suj_512',...] if a subject is deleted you can protect your code by : creating a global_subject_list (permanet or dynamic) global_subject_list.has_key[a_subject] or you can write your own "delete_subject" fonction which will remove from student lists the delete subject the uniques ids act has an indirection allowing to modify the object without breaking any link .... -- _/ _/ _/_/_/ _/_/ Michel.Vayssade@UTC.fr Service Informatique _/ _/ _/ _/ T:33/0-3.44.23.49.24 Universite de Technologie _/ _/ _/ _/ F:33/0-3.44.23.46.77 BP 20.529 60205 Compiegne _/_/ _/ _/_/ _ mv@utc.fr __/www.utc.fr/~vayssade____ France