January 2002 - Zope - Zope lists

ANN: New product for managing relations
by maxm 13 Jan '02

13 Jan '02

It is stable and functional, but only used in one project. So I considder it version 0.0.1. http://www.zope.org/Members/maxm/productList/mxmRelations/ ------------------------------------------------ This is the mxmRelations product It is made to solve a few common problems with Zope's object oriented database. Normally in a relational database some tables will be used to show relations between rows. It can be both "one to many", and "many to many". In Zope, doing the same thing is more difficult than it has to be. The usual way of doing relations in Zope is by using the list widget in a zClass, or to store the relations in a home made list or dictionary for the pupose. There is several problems with this approach. Let's take an examle. The students in classes example Imagine a school with several classes and several students. Some of the students wil take some of the classes. So theres is a relation between some students, and some classes. A simple structure for this in Zope would be to have two folders "classes" and "students":: classes/ class_1 class_2 class_3 ... etc. students/ student_1 student_2 student_3 student_4 Ordinarily in zope you would then write two classes something like:: class Klass: # hmmm, stupid example def __init__(self, id, title): self.id = id self.title = title self.students_in_class = [] class Student: # hmmm, stupid example def __init__(self, id, title): self.id = id self.title = title self.taking_classes = [] The problem is that the two classes have to maintain the same relations. So the picture could be like:: class_1.students_in_class = ['student_1', 'student_2'] class_2.students_in_class = ['student_3', 'student_4'] class_3.students_in_class = ['student_1', 'student_4'] Or you might even keep backwards relations so that you can easily see whitch students takes which classes:: student_1.taking_classes = ['class_1','class_3'] student_2.taking_classes = ['class_1'] student_3.taking_classes = ['class_2'] student_4.taking_classes = ['class_2','class_3'] This is the bad situation where you have to keep two otherwise unrelated sets of relations up to date. In some cases the objects might even be spread out in different folders. Then it can get real ugly fast. You get direct paths in the code, duplication of code and functionality. So then you want to make a listwidget where the user can select which classes that the students take:: <select name="students_in_class:list" multiple> <dtml-in "students.objectValues()"> <option value="<dtml-var "getId()">"><dtml-var "title_or_id()"></option> </dtml-in> </select> And you want those selected to be hilited:: <select name="students_in_class:list" multiple> <dtml-in "students.objectValues()"> <option<dtml-if "getId() in taking_classes" > selected</dtml-if > value="<dtml-var "getId()">"><dtml-var "title_or_id()"></option> </dtml-in> </select> Here is another problem. What if a student drops out, and is deleted from Zope, but is still in some of the "students_in_class" list under some of the class objects. How do we remove the dead relations? One way is to make code ignoring objects no longer in existance:: <select name="students_in_class:list" multiple> <dtml-in "students.objectValues()"> <dtml-try> <option<dtml-if "getId() in taking_classes" > selected</dtml-if > value="<dtml-var "getId()">"><dtml-var "title_or_id()"></option> <dtml-except> </dtml-try> </dtml-in> </select> But that's not really a solution is it? And you have to do it for each and every object that reference another object. Again repetition of code and functionality. Another problem is that a student also can be referenced in the student councel, the school mailinglist, the holiday list etc. Suddenly an object can be related to many different objects. And all of then have to have the same code doing the relational-housholding stuff. Boring! So here's my solution The mxmRelations product handles all the relations. Shows only the valid ones, and deletes the dead and rotten ones. It has a very simple API with only five methods:: ######################################################## # Public methods. def relate(objs1, objs2): """ Sets relations between objects. If there allready is a key it appende the relations else it creates a new key with a list of relations """ def unrelate(objs1, objs2): """ Removes relations between objects """ def delete(obj): """ Removes all references to the object. Used ie. if an object is deleted. """ def get(obj, meta_types=None): """ Returns all relations to this object, or an empty list """ def getSmartList(self, obj, objects, meta_types=None): """ returns a list of objects with parameters (id, title, path, selected) Very usable for making selection widgets, or lists of checkboxes. "obj" is the object that we are looking for relations too. "objects" is a list of objects that we want to know whether they are related to "obj". """ So now the site from before will have the following structure:: relations_class_students # instance of the relation product classes/ class_1 class_2 class_3 ... etc. students/ student_1 student_2 student_3 student_4 And the code to make a list widget is:: <select name="students_in_class:list" multiple> <dtml-in "relations_class_students.getSmartList(this(), students.objectValues())" sort=id> <option value="<dtml-var path>"<dtml-if selected > selected</dtml-if>><dtml-var title></option> </dtml-in> </select>

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Tiny Tables Follow-Up
by Wade Pearce 13 Jan '02

13 Jan '02

As a follow-up to my request, I'd like to thank those that replied. After delving more deeply, we discovered that the Data.fs file had become corrupt. After using fsrecover.py on the file (which cut the last 50KB of transactions), we attempted to resurrect our site. We are somewhat confused as to what happened, but we're trying to find out what. The main reason is that logically, what has happened shouldn't. Here is what we did: With our proper Data.fs file corrupt, we were using an emergency Data.fs which has basic necessities and information. The corrupt Data.fs was named Data.fs.2312 (for when it crashed). The emergency Data.fs was 240MB in size and Data.fs.2312 was 660MB in size. 1) Copied Data.fs.2312 to Data.fs.recover and ran fsrecover.py on it 2) Stopped Zope 3) Moved Data.fs (the emergency copy) to a backup directory. 4) Renamed Data.fs.recover to Data.fs and restarted Zope. The site remained down and inoperative. 5) Stopped Zope. Renamed Data.fs to Data.fs.recover and move Data.fs back from the backup directory. Restarted Zope. 6) Checked the site...and the proper site came up (which was supposed to be in Data.fs.recover). The server has now been running since Friday afternoon with the full site operational. I have tested it. I can add items within the manage screens, the server owner can create export files and the site shows full operatability with the Postgres database behind it. We're waiting for a quiet time to reboot the machine to see if it reverts. We have a suspicion that the site we are viewing is in the cache memory, but as we've never experienced this before, we're kinda stabbing in the dark. Does anybody have any suggestions as to what has happened here? The Data.fs file Zope is supposed to be accessing is the 240MB file. For the life of us, we're stumped. Any ideas, suggestions or speculations welcome. Thanks Wade Pearce Wedge Tail Eagles Australasian Net Gaming Association (http://wtecommand.com) "Powered by Zope"

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Photo: somes issues and thoughts
by J M Cerqueira Esteves 13 Jan '02

13 Jan '02

Greetings I am developing a site where people editing content will not directly access the Zope interface but will use several simplified forms adequate for their work. Since they will occasionally need to add some images, I am using the Photo product as the basis for the image management tool they will be using (images will be Photo objects in a hierarchy of Photo Folders, and most people will not be writing DTML but referring to original images or derived displays explicitly writing their URLs in plain HTML). While preparing this, I noticed a few minor issues. On-the-fly resizing could be interesting: Ron Bickers seems to be considering adding support for on-the-fly image resizing, that is, arbitrary image resizing with no need for predefining named display sizes. This could be convenient for situations like my current one. There will be a few cases where the "photo album" metaphor will be used (like in the Photo Folder sample views), but the majority of the other pictures will be added one by one to be used in separate contexts, each in one or two sizes without any foreseeable "size standards". For many pictures, display sizes will have to be defined individually, therefore with less interest in having to "invent" or reuse a name for each new size or even to have to visit an administration interface just for resizing; maybe the nicest solution from the point of view of a content editor (when not working with the "tag" method but only writing pure HTML) would be simply to write <img src="http:/somesite/img/.../picture.jpg?width=300" ... /> when one needs to show picture.jpg in a new size with width of 300 pixels or .../picture.jpg?width=480&height=480 to limite the larger size to 480 pixels. This would end up producing "unnamed" cached displays for each picture. Of course HTML authors would still have to take care of checking the final dimensions in order to write 'height' and 'width' attributes... or those could be supplied by a size testing interface on the site (possibly listing already cached sizes). It could also be nice to allow rescaling (relatively to the original size) with something like .../picture.jpg?scale=1.56 (or a "scale" cookie perhaps of use for automagically resizing all images (big and small) by the same factor on a set of pages via a "scale" cookie). One could then wish for several other image transformations like those available with \includegraphics in LaTeX package graphicx: cropping with "bounding boxes", rotation, ... :-) About the cookie name: It could also be useful to allow customization of the cookie name (now hardcoded as 'display') to solve possible cases of "collision" with other cookies or even to allow separate display customization for different image sets in the same site. Likewise for any other cookies which may someday be used by the Photo product. The `tag' method: The `tag' method sets the display cookie only when the supplied display name corresponds to an existing one for the current image. An interesting exception would be to set the display cookie ALSO when display=='', thus activating "natural size" viewing (unless one has defined a display size with id=='', which is currently possible...). Ideally, the `tag' method should respect alt=='' (since sometimes one really wants that): if alt is None: alt = getattr(self, 'title', None) if alt is None: alt = self.getId() Image size calculation: In my "view" method (replacing the sample "view") I was going to show the dimensions the current pic would have at each defined display size, near to the link to the corresponding page. It would be interesting to have public methods providing that information (height() and width() only provide it for the original image; displayMap() only provides dimensions for displays which have already been generated, and I chose not to pregenerate them all). I simply reproduced the calculations of _getAspectRatioSize, but then noticed that some results were wrong. For instance, with an original image of 272×281 pixels, the result of rezising to a maximum of 480×480 is not an image with 464×480 as expected, but 464×479. This happens because I opted for using ImageMagick and: - _getAspectRatioSize, using integer division, rounds down 464.626334... (the "ideal" new width) to 464; - _resize calls ImageMagick's `convert' with option -geometry 464x480; - called like this, `convert' also tries to mantain the aspect ratio of the input image and uses the -geometry parameters as limits: constrained to 464×480, the best solution it finds to maintain the aspect ratio is creating an image of 464×479. It would be better in this case to call `convert' with option -geometry 480x480 and let it calculate the ideal new size. When I do that manually, I get a 465×480 image. Unfortunately, I had no time to determine the precise equation used by ImageMagick to calculate new sizes maintaining aspect ratio. Having it, you could use that instead of the calculation at _getAspectRatioSize when resizing with PIL (since PIL's `resize', unlike ImageMagick's `convert', doesn't try to maintain aspect ratio and needs to be given precise final sizes). Image quality with PIL: I noticed that in the version of PIL I have here, 1.1.2, the resize method has an optional filter argument which can be "NEAREST, BILINEAR, or BICUBIC. If omitted, it defaults to NEAREST." I have no time for careful testing now (and Image Magick is working very well), but noticed that `resize' is being without specifying the filter, thus using NEAREST and not taking full advantage of PIL capabilities. Best regards J Esteves

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Passing arguments when calling precondition
by Jánvári Gusztáv 12 Jan '02

12 Jan '02

Could anybody tell me a reliable method on how to pass arguments for a script/method employed as precondition for some File objects? What I'd like to do is to pass a record identifier to the method called as precondition, increase a download counter in a database, then let the visitor download the given file. If the record identifier would be None, an exception could be thrown, thus denying access to the file. In this case I wouldn't bother with users who try to enter absolute URL with a valid record identifier known e.g. by accident for the files requiring registration before downloading, since the download counter would work and that's all what I want. e-Musty

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RE: [Zope] Corrupt ZODB on W2k
by Tom Cameron 12 Jan '02

12 Jan '02

Chris, => Have you tried checking your backups to pinpoint when the corruption => happened? To be honest, the problem is in a client's machine and has only happened twice in a year. They are not willing to pay me to investigate and I just dont have the time for such work. => One final thing, I find it interesting that exporting and => importing seems to fix your problem. More interesting, I find that export+import as .zexp does not work, but exporting+import as .xml does work. I really dont know much about the difference, but the .zexp seems to just grab a chunk of the ZODB errors and all, but .xml is a true export of the data. Anyway, I sent this message off for discussion purposes, we have fixed the problem and moved on. I am just curious about why this happened and if others have similar experiences. Tom

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Exporting or saving File object to the server's local file system from Zope
by e-Musty 12 Jan '02

12 Jan '02

I have several files stored in a Folder, but I gonna to use a LocalFileSystem object to hold those files. Since the server is a bit far away from my chair, I wouldn't like to play with downloading files one-by-one from Zope, then upload those to the server. Could somebody tell me a way, how to export files of a folder to the server's file system? Standard Import/Export functions has two problems, namely that (a) even if exporting a single File, it will be saved as a zexp, and that (b) LocalFileSystem does not support paste or import/export (only cut and copy). All hints appreciated, e-Musty

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ZOQL Feedback
by Stephan Richter 12 Jan '02

12 Jan '02

Hello everyone, after I released ZOQLMethod 0.4.0 dev preview, some people voted in the online poll that they did not like ZOQL, since it is inconsistent. Unfortunately, I did not provide a comments field, where people could elaborate some more. Therefore I am writing to the list asking people of why they think about ZOQL the way they do negative and positive and I hope that Thomas Foerster (really the main developer behind ZOQLMethod, having written the Parser and much more) and I will be able to implement the suggestions. We both want that product to be useful. It should help the user (you) to develop your applications quicker and fill in a major hole in the framework (i.e.: provide a query language for the ZODB). Thanks a lot for your time! Regards, Stephan -- Stephan Richter CBU - Physics and Chemistry Student Web2k - Web Design/Development & Technical Project Management

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Auto render validated values in Formulator
by Trevor Toenjes 12 Jan '02

12 Jan '02

I am trying to auto-render the results of a form. <dtml-call "form.validate_all_to_request(REQUEST)"> <dtml-in "form.get_fields()"> <dtml-let field=sequence-item> <dtml-var "field.get_value('description')"><br> <dtml-var field><p> <----offending dtml </dtml-let> </dtml-in> However, this displays nothing for 'field'. <dtml-var "field.render_from_request(REQUEST)"> displays the values, but in the full HTML form (undesired) Manually, <dtml-var myfieldname> renders properly, so I am being tripped up by object types. What am I missing? TIA -Trevor

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Tree tag and lists.
by Josef Meile 12 Jan '02

12 Jan '02

I want to create a bullet list with the tree tag. My idea is to have a list of topics which can be expanded and collapsed. Each time the user clicks on a collapsed node, a text will be shown. My problem is that I don't know how I can use this tag with a list, ie: [['Title1','description1'],['Title2','description2'],...,['Titlen','descriptionn']] Does somebody have an idea? Thanks in advanced, Josef.

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Script (python) shows transaction for adding folder
by Tim Hicks 12 Jan '02

12 Jan '02

I have a script that accepts an html form entry (submitted from a dtml-document) and tries to do various file uploads into the zodb (actually, they are ExtImages). All of this works (pretty well), but in testing, I've noticed that each time my script performs this form validation/submission process, there is a new transaction present in the undo list. The transaction refers to adding a folder (and probably another one to add the actual image) to the zodb for the upload. So, my question is, why does the transaction appear in the undo list for the script, and not the parent folder I'm adding to (which is a BTree folder if that makes any difference)? I guess it's not a problem, just seems a bit odd to me. thanks tim

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