Re: [Zope3-Users] searching and relations
Gary Poster wrote: If the relationship is intrinsic to one object's data model but not to the other's, then it makes sense to have a Python pointer on the first object. Hi Gary, Am I right that 'a Python pointer on the first object' is defined by simply defining the schema field, eg:: mypointer = Object( title=Pointer to object, schema=IInterfaceOfTheTarget) Then everything else will fall into place. I could even use formlib to edit the object being pointed to from within a form editing the 'first object'. The second object would not even know it is pointed to. For it to know I would need to use a relationship as you go on to discuss. Have a correctly understood? Regards, Darryl ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] searching and relations
On Jul 23, 2006, at 4:12 AM, Darryl Cousins wrote: Gary Poster wrote: If the relationship is intrinsic to one object's data model but not to the other's, then it makes sense to have a Python pointer on the first object. Hi Gary, Am I right that 'a Python pointer on the first object' is defined by simply defining the schema field, eg:: mypointer = Object( title=Pointer to object, schema=IInterfaceOfTheTarget) Then everything else will fall into place. I could even use formlib to edit the object being pointed to from within a form editing the 'first object'. The second object would not even know it is pointed to. For it to know I would need to use a relationship as you go on to discuss. Have a correctly understood? Yes, precisely; and for what it is worth, the Object schema value lets formlib work, and specifies part of your software's contract, but is not necessary for the most basic story. The simplest clear case (Where `app` represents some ZODB folder, like the application root): class DemoSubject(persistent.Persistent): pass class DemoObject(persistent.Persistent): pass app['demo'] = DemoSubject() app['demo'].mypointer = DemoObject() By the way, a small but possibly important subtlety about the object widgets that are associated with the schema object fields is that (unless you manage your form pretty carefully) they change value by creating new instances of the sub-object and replacing it on the main object, not by modifying an old sub-object instance, IIRC. Sometimes Choice fields with a custom vocabulary or source are what you want, if you want to make a pointer to an object that already exists somewhere in the database. Gary ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] searching and relations
El vie, 21-07-2006 a las 10:21 -0400, Pete Taylor escribió: Lorenzo, I've run into a very (very!) similar situation, and ended up writing some wrapper/simplification utilities for zc.relationship. zc.relationship is wonderfully powerful, but a bit complex. It's use is intuitive once you wade through the 2000+ lines of documentation (which is worthwhile reading), but it's a bit intimidating at first. Ok, I was afraid of an answer like this because in a recent thread I've read Jim Fulton saying that we are trying to use zodb as a relational database which is a shame and I think I agree with that quote. So that's why I tried not to use external packages like zc.relationship and stick to a plain object model with intrinsic relations modeled as simple object attributes. The obvious question is: does this allow powerful queries like the ones I mentioned in my first email or I should switch and use extrinsic relations for this kind of features? I've packaged up my wrapper utilities as a product, and ZPL2.1'd the code. If you'd like it, even just for reference, let me know. I intend to release it more publicly shortly. Sure! I'm 120% interested in reading your solution since reinventing the wheel is something I always try to avoid. Thanks a lot for you kindly offer! Lorenzo It implements nice adapters, so objects implementing a particular marker interface can do things like: client = MyClient() q = IQuestion(obj) orders = q.ask_as_subject(owns) orders ['some.Order object at...'] you can also build filter functions that take the relationship you're targeting as an argument, and check any property of the relationship in question... let me know if you'd like a copy. if not, then i'd suggest going through at least the containers.txt in zc.relationship. as far as the catalog goes, i'd get into using hurry.query as fast as possible ;) On 7/21/06, Lorenzo Gil Sanchez [EMAIL PROTECTED] wrote: Hi, I've been following recent discussion about relations in Zope. Both intrinsic and extrinsic relationships. For the following question lets assume we have a IClient and an IOrder content types and the IOrder schema has a IClient attribute called 'client'. Reading previous messages to this list I understand that's the best way to model this kind of intrinsic relationship between an Order and a Client. Now the question: using a Catalog, what should I do to answer these kind of questions: - Give me all orders whose client's name starts with 'John' - Give me all orders whose client's age is between 20 and 30 - Give me all orders for a certain client I guess I need to use a special kind of FieldIndex for objects but I'm new to the Catalog land and I'm pretty much lost. Any help, examples or pointers to detailed doc are greatly appreciated :-) Best regards, Lorenzo Gil ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] searching and relations
On Jul 22, 2006, at 4:47 AM, Lorenzo Gil Sanchez wrote: El vie, 21-07-2006 a las 10:21 -0400, Pete Taylor escribió: Lorenzo, I've run into a very (very!) similar situation, and ended up writing some wrapper/simplification utilities for zc.relationship. zc.relationship is wonderfully powerful, but a bit complex. It's use is intuitive once you wade through the 2000+ lines of documentation (which is worthwhile reading), but it's a bit intimidating at first. Ok, I was afraid of an answer like this because in a recent thread I've read Jim Fulton saying that we are trying to use zodb as a relational database which is a shame and I think I agree with that quote. So that's why I tried not to use external packages like zc.relationship and stick to a plain object model with intrinsic relations modeled as simple object attributes. Heh. I gave that Jim Fulton quote, and encouraged the direction you describe; *and* I wrote zc.relationship. ;-) They are not mutually exclusive. Let's take a simple two-member directional relationship as an example--something like A depends on B. If neither object should inherently know about the relationship--it's not intrinsic to either of their data models--then it makes good sense to have external relationship objects that model the connection. The relationship container in zc.relationship is a simple example of a solution for that use case. If the relationship is intrinsic to one object's data model but not to the other's, then it makes sense to have a Python pointer on the first object. If you need to ask questions, such as simple backpointers, then you can set up an extrinsic reference or you can set up a zc.relationship index to index the first object. For a simple backpointer case, an extrinsic reference is sufficient and simpler. If you need more sophisticated queries than just backpointers then the zc.relationship index can be a real win: you can adapt the first object to a relationship interface that breaks the relationship down into parts that match the queries you want to make. That works nicely. If the relationship is intrinsic to both objects' data models, all you can really do is choose one of the previous two approaches and put some sugar around it. AIUI, schooltool's relationship code does something like this: you can specify both sides of a relationship in a class definition (and an interface, I believe) and behind the scenes it keeps track of the relationship for you in an external data structure, no matter which side of the relationship you modify. zc.relationship's index could be used to build functionality like this, but it has not been done to my knowledge. The obvious question is: does this allow powerful queries like the ones I mentioned in my first email or I should switch and use extrinsic relations for this kind of features? zc.relationship indexes can be combined with other catalog indexes to do what you described, but doing so efficiently will require knowledge of catalog indexes and the BTree module. The README for zc.relationship touches on this when it discusses filters: | If relationship tokens (from 'findRelationshipChains' or 'apply' or | 'findRelationshipTokenSet', or in a filter to most of the search methods) are | to be merged with other catalog results, relationship tokens should be based | on intids, as in the default. For instance, if some relationships are only | available to some users on the basis of security, and you keep an index of | this, then you will want to use a filter based on the relationship tokens | viewable by the current user as kept by the catalog index. The filter is not the only approach--you will sometimes want to merge *results* from a relationship index and other indexes, for instance-- but if you are doing transitive searches it may be preferred for efficiency. zc.relationship is a bit of a powertool. Projects like the one Pete describes to make a friendly, more constrained usage of it will be very useful. Also, don't forget SQL. I prefer the ZODB, and stay there if I can make a reasonably convincing case (almost always ;-) ), but sometimes an app really calls out for a hybrid approach. Gary___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
[Zope3-Users] searching and relations
Hi, I've been following recent discussion about relations in Zope. Both intrinsic and extrinsic relationships. For the following question lets assume we have a IClient and an IOrder content types and the IOrder schema has a IClient attribute called 'client'. Reading previous messages to this list I understand that's the best way to model this kind of intrinsic relationship between an Order and a Client. Now the question: using a Catalog, what should I do to answer these kind of questions: - Give me all orders whose client's name starts with 'John' - Give me all orders whose client's age is between 20 and 30 - Give me all orders for a certain client I guess I need to use a special kind of FieldIndex for objects but I'm new to the Catalog land and I'm pretty much lost. Any help, examples or pointers to detailed doc are greatly appreciated :-) Best regards, Lorenzo Gil ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] searching and relations
Lorenzo, I've run into a very (very!) similar situation, and ended up writing some wrapper/simplification utilities for zc.relationship. zc.relationship is wonderfully powerful, but a bit complex. It's use is intuitive once you wade through the 2000+ lines of documentation (which is worthwhile reading), but it's a bit intimidating at first. I've packaged up my wrapper utilities as a product, and ZPL2.1'd the code. If you'd like it, even just for reference, let me know. I intend to release it more publicly shortly. It implements nice adapters, so objects implementing a particular marker interface can do things like: client = MyClient() q = IQuestion(obj) orders = q.ask_as_subject(owns) orders ['some.Order object at...'] you can also build filter functions that take the relationship you're targeting as an argument, and check any property of the relationship in question... let me know if you'd like a copy. if not, then i'd suggest going through at least the containers.txt in zc.relationship. as far as the catalog goes, i'd get into using hurry.query as fast as possible ;) On 7/21/06, Lorenzo Gil Sanchez [EMAIL PROTECTED] wrote: Hi, I've been following recent discussion about relations in Zope. Both intrinsic and extrinsic relationships. For the following question lets assume we have a IClient and an IOrder content types and the IOrder schema has a IClient attribute called 'client'. Reading previous messages to this list I understand that's the best way to model this kind of intrinsic relationship between an Order and a Client. Now the question: using a Catalog, what should I do to answer these kind of questions: - Give me all orders whose client's name starts with 'John' - Give me all orders whose client's age is between 20 and 30 - Give me all orders for a certain client I guess I need to use a special kind of FieldIndex for objects but I'm new to the Catalog land and I'm pretty much lost. Any help, examples or pointers to detailed doc are greatly appreciated :-) Best regards, Lorenzo Gil ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users -- All guilt is relative, loyalty counts, and never let your conscience be your guide. - Lucas Buck, American Gothic ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
