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• Coupling an MFC CListCtrl and CTreeCtrl to get a view of the whole tree, not just one node at a time

  - by omatai

  Consider Windows Explorer (or regedit or similar). To the left side, there is a tree view, and to the right, a list view. In all cases I know of, the contents of the right view reflect the attributes of the selected node from the left pane. This is all well and good... but just not what I want. The nodes of the tree I want to display have a very few attributes (2-3) associated with each node - a reasonable amount to display horizontally as a row in a table. Rather than waste all that list view space on a single node with very few properties, I would like to have my list view display a table of the whole tree's properties (as the part of the tree currently expanded). So the nth line in the left view (tree) will correspond directly to the nth line in the right view (list/table), and I will get a decent overview of the properties of my tree. Does anyone know of code that does this? I am guessing that slaving a CListCtrl to a CTreeCtrl would be the way to go, and somehow overriding the vertical scrolling functions so that they are locked together. I'm just not sure that it is possible to lock the scrolls together like this... among other things! All advice gratefully welcomed :-)

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• Reasonably faster way to traverse a directory tree in Python?

  - by Sridhar Ratnakumar

  Assuming that the given directory tree is of reasonable size: say an open source project like Twisted or Python, what is the fastest way to traverse and iterate over the absolute path of all files/directories inside that directory? I want to do this from within Python (subprocess is allowed). os.path.walk is slow. So I tried ls -lR and tree -fi. For a project with about 8337 files (including tmp, pyc, test, .svn files): $ time tree -fi > /dev/null real 0m0.170s user 0m0.044s sys 0m0.123s $ time ls -lR > /dev/null real 0m0.292s user 0m0.138s sys 0m0.152s $ time find . > /dev/null real 0m0.074s user 0m0.017s sys 0m0.056s $ tree appears to be faster than ls -lR (though ls -R is faster than tree, but it does not give full paths). find is the fastest. Can anyone think of a faster and/or better approach? On Windows, I may simply ship a 32-bit binary tree.exe or ls.exe if necessary. Update 1: Added find

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• How do we keep dependent data structures up to date?

  - by Geo

  Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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• Dynamically evaluating simple boolean logic in Python

  - by a paid nerd

  I've got some dynamically-generated boolean logic expressions, like: (A or B) and (C or D) A or (A and B) A empty - evaluates to True The placeholders get replaced with booleans. Should I, Convert this information to a Python expression like True or (True or False) and eval it? Create a binary tree where a node is either a bool or Conjunction/Disjunction object and recursively evaluate it? Convert it into nested S-expressions and use a Lisp parser? Something else? Suggestions welcome.

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• Scala: working around the "illegal cyclic reference"

  - by Paul Milovanov

  Hi all, I'm trying to implement a HashMap-based tree that'd support O(1) subtree lookup for a given root key. To that goal, I'm trying to do the following: scala> type Q = HashMap[Char, Q] <console>:6: error: illegal cyclic reference involving type Q type Q = HashMap[Char, Q] ^ So the question is, is there a way for me to do something of the sort without resorting to the ugly HashMap[Char, Any] with subsequent casting of values to HashMap[Char, Any]? Now, I also see that I can use something like the following to avoid the cyclic-reference error, and it might even be cleaner -- but it'd be nice to find out how to correctly do it the first way, just for the educational value. import collections.mutable.HashMap class LTree { val children = new HashMap[Char, LTree] } Thanks a bunch.

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• What's the best general programming book to review basic development concepts?

  - by Charles S.

  I'm looking for for a programming book that reviews basic concepts like implementing linked lists, stacks, queues, hash tables, tree traversals, search algorithms, etc. etc. Basically, I'm looking for a review of everything I learned in college but have forgotten. I prefer something written in the last few years that includes at least a decent amount of code in object-oriented languages. This is to study for job interview questions but I already have the "solving interview questions" books. I'm looking for something with a little more depth and explanation. Any good recommendations?

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• Best design for generating code from an AST?

  - by Sam Washburn

  I'm working on a pretty complex DSL that I want to compile down into a few high level languages. The whole process has been a learning experience. The compiler is written in java. I was wondering if anyone knew a best practice for the design of the code generator portion. I currently have everything parsed into an abstract syntax tree. I was thinking of using a template system, but I haven't researched that direction too far yet as I would like to hear some wisdom first from stack overflow. Thanks!

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• Recursive Function To Create Array

  - by mTuran

  Hi, i use kohana framework and i am trying to code recursive function to create category tree. My Categories Table id int(11) NO PRI NULL auto_increment name varchar(50) NO NULL parent_id int(11) NO NULL projects_count int(11) NO NULL My Example Which Is Not Work public static function category_list($parent_id = 0) { $result = Database::instance()->query(' SELECT name, projects_count FROM project_categories WHERE parent_id = ?', array($parent_id) ); $project_categories = array(); foreach($result as $row) { $project_categories[] = $row; Project_Categories_Model::factory()->category_list($parent_id + 1); } return $project_categories; }

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• Get HTML DOM with CSS

  - by 2x2p1p

  CSS can apply styles in elements through one ID, class or pseudo-selector, but I would like to get the HTML tree, something like in javascript: <script type = "text/javascript"> window.onload = function () { var div = document.getElementsByTagName ("div"); div[0].style.backgroundColor = "gray"; div[0].style.padding = "20px"; } </script> So for example: <style type = "text/css"> div[0] { /* Wrong but i tried :( */ background-color: gray; padding: 20px; } </style> <div > <div>...</div> </div> I'm tired of assign IDs to millions and millions of elements; is there a way to do this?

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• Problem understanding treesort in Haskell

  - by Jerry

  I am trying to figure out how exactly does treesort from here work (I understand flatten, insert and foldr). I suppose what's being done in treesort is applying insert for each element on the list thus generating a tree and then flattening it. The only problem I can't overcome here is where the list (that is the argument of the function) is hiding (because it is not written anywhere as an argument except for the function type declaration). One more thing: since dot operator is function composition, why is it an error when I change: treesort = flatten . foldr insert Leaf to treesort = flatten( foldr insert Leaf )?

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• Json to treeview (<ul>)

  - by Pieter

  Hi I get the following data back from my WCF Data Service (I cut out the metadata) { "d" : [ {"CodeId": 6, "Title": "A Child Sub Item", "Parent":}, {"CodeId": 5, "Title": "Another Root Item", "Parent": -1}, {"CodeId": 4, "Title": "Child Item", "Parent": 2}, {"CodeId": 2, "Title": "Root Item", "Parent": -1} ] } I am trying to get this into a <ul> style tree with Parent = -1 as root and then the rest as sub items of their parent id's. Can anyone help me please, preferably in jQuery? I will use this in jstree if someone knows of a better way to do this. Thanks

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• Turn database result into array

  - by Industrial

  Hi everyone, I have just made the update/add/delete part for the "Closure table" way of organizing query hierarchical data that are shown on page 70 in this slideshare: http://www.slideshare.net/billkarwin/sql-antipatterns-strike-back My database looks like this: Table Categories: ID Name 1 Top value 2 Sub value1 Table CategoryTree: child parent 1 1 2 2 2 1 However, I have a bit of an issue getting the full tree back as an multidimensional array from a single query. Here's what I would like to get back: array ( 'topvalue' = array ( 'Subvalue', 'Subvalue2', 'Subvalue3' = array ('Subvalue 1', 'Subvalue 2', 'Subvalue 3' ) ); ); Update: Found this link, but I still have a hard time to convert it into an array: http://karwin.blogspot.com/2010/03/rendering-trees-with-closure-tables.html

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• mySQL INSERT INTO SELECT not working

  - by Industrial

  Hi everyone, I am trying to implement the "Closure Table" structure in a php/mySQL webapp from Bill Karwins "SQL Antipatterns" slideshare presentation: http://www.slideshare.net/billkarwin/sql-antipatterns-strike-back The first step is to insert some stuff into my tree (page 73 in slide): Easy to insert a new child of comment #5: INSERT INTO Comments ... (Generates comment #8) INSERT INTO TreePaths (ancestor, descendant) VALUES (8, 8); INSERT INTO TreePaths (ancestor, descendant) SELECT ancestor, 8 FROM TreePaths WHERE descendant = 5; I try to translate all this into Codeigniters active record db-style language, and that's about where I get stuck. I cant understand how the second insert gets it's values. Is there anyone out there who can help me out with this?

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• Updating cached counts in MySQL

  - by phleet

  In order to fix a bug, I have to iterate over all the rows in a table, updating a cached count of children to what its real value should be. The structure of the things in the table form a tree. In rails, the following does what I want: Thing.all.each do |th| Thing.connection.update( " UPDATE #{Thing.quoted_table_name} SET children_count = #{th.children.count} WHERE id = #{th.id} " ) end Is there any way of doing this in a single MySQL query? Alternatively, is there any way of doing this in multiple queries, but in pure MySQL? I want something like UPDATE table_name SET children_count = ( SELECT COUNT(*) FROM table_name AS tbl WHERE tbl.parent_id = table_name.id ) except the above doesn't work (I understand why it doesn't).

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• Don’t be a dinosaur. Use Calendar Tree!

  - by jamiet

  If one spends long enough in my company one will likely eventually have to listen to me bark on about subscribable calendars. I was banging on about them way back in 2009, I’ve cajoled SQLBits into providing one, provided one myself for the World Cup, and opined that they could be transformative for the delivery of BI. I believe subscribable calendars can change the world but have never been good at elucidating why I thought so, for that reason I always direct people to read a blog by Scott Adams (yes, the guy who draws Dilbert) entitled Calendar as Filter. In that blog post Scott writes: I think the family calendar is the organizing principle into which all external information should flow. I want the kids' school schedules for sports and plays and even lunch choices to automatically flow into the home calendar. Everything you do has a time dimension. If you are looking for a new home, the open houses are on certain dates, and certain houses that fit your needs are open at certain times. If you are shopping for some particular good, you often need to know the store hours. Your calendar needs to know your shopping list and preferences so it can suggest good times to do certain things I think the biggest software revolution of the future is that the calendar will be the organizing filter for most of the information flowing into your life. You think you are bombarded with too much information every day, but in reality it is just the timing of the information that is wrong. Once the calendar becomes the organizing paradigm and filter, it won't seem as if there is so much. I wholly agree and hence was delighted to discover (via the Hanselminutes podcast) that Scott has a startup called CalendarTree.com whose raison d’etre is to solve this very problem. What better way to describe a Scott Adams startup than with a Scott Adams comic: I implore you to check out Calendar Tree and make the world a tiny bit better by using it to share any information that has a time dimension to it. Don’t be a dinosaur, use Calendar tree! @Jamiet

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• Does it matter the direction of a Huffman's tree child node?

  - by Omega

  So, I'm on my quest about creating a Java implementation of Huffman's algorithm for compressing/decompressing files (as you might know, ever since Why create a Huffman tree per character instead of a Node?) for a school assignment. I now have a better understanding of how is this thing supposed to work. Wikipedia has a great-looking algorithm here that seemed to make my life way easier. Taken from http://en.wikipedia.org/wiki/Huffman_coding: Create a leaf node for each symbol and add it to the priority queue. While there is more than one node in the queue: Remove the two nodes of highest priority (lowest probability) from the queue Create a new internal node with these two nodes as children and with probability equal to the sum of the two nodes' probabilities. Add the new node to the queue. The remaining node is the root node and the tree is complete. It looks simple and great. However, it left me wondering: when I "merge" two nodes (make them children of a new internal node), does it even matter what direction (left or right) will each node be afterwards? I still don't fully understand Huffman coding, and I'm not very sure if there is a criteria used to tell whether a node should go to the right or to the left. I assumed that, perhaps the highest-frequency node would go to the right, but I've seen some Huffman trees in the web that don't seem to follow such criteria. For instance, Wikipedia's example image http://upload.wikimedia.org/wikipedia/commons/thumb/8/82/Huffman_tree_2.svg/625px-Huffman_tree_2.svg.png seems to put the highest ones to the right. But other images like this one http://thalia.spec.gmu.edu/~pparis/classes/notes_101/img25.gif has them all to the left. However, they're never mixed up in the same image (some to the right and others to the left). So, does it matter? Why?

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• Script/tool to import series of snapshots, each being a new revision, into Subversion, populating source tree?

  - by Rob

  I've developed code locally and taken a fairly regular snapshot whenever I reach a significant point in development, e.g. a working build. So I have a long-ish list of about 40 folders, each folder being a snapshot e.g. in ascending date YYYYMMDD order, e.g.:- 20100523 20100614 20100721 20100722 20100809 20100901 20101001 20101003 20101104 20101119 20101203 20101218 20110102 I'm looking for a script to import each of these snapshots as a new subversion revision to the source tree. The end result being that the HEAD revision is the same as the last snapshot, and other revisions are as numbered. Some other requirements: that the HEAD revision is not cumulative of the previous snapshots, i.e., files that appeared in older snapshots but which don't appear in later ones (e.g. due to refactoring etc.) should not appear in the HEAD revision. meanwhile, there should be continuity between files that do persist between snapshots. Subversion should know that there are previous versions of these files and not treat them as brand new files within each revision. Some background about my aim: I need to formally revision control this work rather than keep local private snapshot copies. I plan to release this work as open source, so version controlling would be highly recommended I am evaluating some of the current popular version control systems (Subversion and GIT) BUT I definitely need a working solution in Subversion. I'm not looking to be persuaded to use one particular tool, I need a solution for each tool I am considering as I would also like a solution in GIT (I will post an answer separately for GIT so separate camps of folks who have expertise in GIT and Subversion will be able to give focused answers on one or the other). The same question but for GIT: Script/tool to import series of snapshots, each being a new edition, into GIT, populating source tree? An outline answer for Subversion in stackoverflow.com but not enough specifics about the script: what commands to use, code to check valid scenarios if necessary - i.e. a working script basically. http://stackoverflow.com/questions/2203818/is-there-anyway-to-import-xcode-snapshots-into-a-new-svn-repository

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• Jasmine testing coffeescript expect(setTimeout).toHaveBeenCalledWith

  - by Lee Quarella

  In the process of learning Jasmine, I've come to this issue. I want a basic function to run, then set a timeout to call itself again... simple stuff. class @LoopObj constructor: -> loop: (interval) -> #do some stuff setTimeout((=>@loop(interval)), interval) But I want to test to make sure the setTimeout was called with the proper args describe "loop", -> xit "does nifty things", -> it "loops at a given interval", -> my_nifty_loop = new LoopObj interval = 10 spyOn(window, "setTimeout") my_nifty_loop.loop(interval) expect(setTimeout).toHaveBeenCalledWith((-> my_nifty_loop.loop(interval)), interval) I get this error: Expected spy setTimeout to have been called with [ Function, 10 ] but was called with [ [ Function, 10 ] ] Is this because the (-> my_nifty_loop.loop(interval)) function does not equal the (=>@loop(interval)) function? Or does it have something to do with the extra square brackets around the second [ [ Function, 10 ] ]? Something else altogther? Where have I gone wrong?

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• Excel, Pivot Calculated formula: SUM(Field1)/AVG(Field2)

  - by Bas

  I've a simple table with some amount and interval in sec by date and product name. Month | Product | Amount | Interval in sec ------------------------------------------ 05-'12| Prod A | 10 | 5 05-'12| Prod A | 3 | 5 05-'12| Prod B | 4 | 5 05-'12| Prod C | 13 | 5 05-'12| Prod C | 5 | 5 From this table I've derived a Pivot table with SUM(Amount), AVERAGE(Interval in sec) by Month and Product. Month | Product | SUM of Amount | AVG of Interval in sec -------------------------------------------------------- 05-'12| Prod A | 13 | 5 05-'12| Prod B | 4 | 5 05-'12| Prod C | 18 | 5 So far So good... Now i want to add and extra column to my Pivot table with gives me the outcome of SUM of Amount / AVG of Interval in sec Adding a calculated value =SUM(Amount)/AVERAGE(Interval) is not giving me the right values. Exel gives me. Month | Product | SUM of Amount | AVG of Interval in sec | Amount per sec ------------------------------------------------------------------------- 05-'12| Prod A | 13 | 5 | 1.3 05-'12| Prod B | 4 | 5 | 0.8 05-'12| Prod C | 18 | 5 | 1.8 What it actually is doing is =SUM(Amount)/SUM(Interval in sec) for every Month and Product based on the values in the first table... But I'm looking for Month | Product | SUM of Amount | AVG of Interval in sec | Amount per sec ------------------------------------------------------------------------- 05-'12| Prod A | 13 | 5 | 2.6 05-'12| Prod B | 4 | 5 | 0.8 05-'12| Prod C | 18 | 5 | 3.6 So litterly devide pivot field 'Sum of Amount' by pivot field 'AVG of Interval in sec' How to achieve this? Thank you in advanced

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• Newbie database index question

  - by RenderIn

  I have a table with multiple indexes, several of which duplicate the same columns: Index 1 columns: X, B, C, D Index 2 columns: Y, B, C, D Index 3 columns: Z, B, C, D I'm not very knowledgeable on indexing in practice, so I'm wondering if somebody can explain why X, Y and Z were paired with these same columns. B is an effective date. C is a semi-unique key ID for this table for a specific effective date B. D is a sequence that identifies the priority of this record for the identifier C. Why not just create 6 indexes, one for each X, Y, Z, B, C, D? I want to add an index to another column T, but in some contexts I'll only be querying on T alone while in others I will also be specifying the B, C and D columns... so should I create just one index like above or should I create one for T and one for (T, B, C, D)? I've not had as much luck as expected when googling for comprehensive coverage of indexing. Any resources where I can get a through explanation and lots of examples of B-tree indexing?

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• Out of Core Implementation of a Quadtree

  - by Nima

  Hi, I am trying to build a Quadtree data structure(or let's just say a tree) on the secondary memory(Hard Disk). I have a C++ program to do so and I use fopen to create the files. Also, I am using tesseral coding to store each cell in a file named with its corresponding code to store it on the disk in one directory. The problem is that after creating about 1,100 files, fopen just returns NULL and stops creating new files. I can create further files manually in that directory, but using C++ it can not create any further files. I know about max limit of inode on ext3 filesystem which is (from Wikipedia) 32,000 but mine is way less than that, also note that I can create files manually on the disk; just not through fopen. Also, I really appreciate any idea regarding the best way to store a very dynamic quadtree on disk(I need the nodes to be in separate files and the quadtree might have a depth of 50). Using nested directories is one idea, but I think it will slow down the performance because of following the links on the filesystem to access the file. Thanks, Nima

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• Installing sfJqueryTreeDoctrineManagerPlugin to Symfony 1.4

  - by Christine Q.

  I have faced serious difficulties while installing sfJqueryTreeDoctrineManagerPlugin to Symfony 1.4 w/ Doctrine ORM. The installation directly from the server did not work out like with previous plugins that I have installed: C:\pathsymfony plugin:install sfJqueryTreeDoctrineManagerPlugin plugin installing plugin "sfJqueryTreeDoctrineManagerPlugin" No release available for plugin "sfJqueryTreeDoctrineManagerPlugin" This is why I needed to install the plugin by downloading the tgz-archive and install it manually like this: C:\pathsymfony plugin:install "C:\path\to\downloads\sfJqueryTreeDoctrineManagerPlugin-1.2.4.tgz" plugin installing plugin "C:\path\to\downloads\sfJqueryTreeDoctrineManagerPlugin-1.2.4.tgz" sfSymfonyPluginManager Installing web data for plugin I guess everything should be fine this far? After that I edited \apps\admin\config\settings.yml like instructed in the plugins readme file. all: .settings: enabled_modules: [default, sfJqueryTreeDoctrineManager] I also checked that the plugin was enabled in \config\ProjectConfiguration.class.php like this: $this->enablePlugins(array( // other plugins, 'sfJqueryTreeDoctrineManagerPlugin' )); I published assets and cleared cache: C:\pathsymfony plugin:publish-assets >> plugin Configuring plugin - sfJqueryTreeDoctrineManagerPlugin C:\pathsymfony cc Finally I added the required helper to the newly created apps\admin\modules\category\templates\indexSuccess.php <?php use_helper("sfJqueryTreeDoctrine"); echo get_nested_set_manager("Category", "name"); When loading the page I unfortunately get the following error: 500 | Internal Server Error | InvalidArgumentException Unable to load "sfJqueryTreeDoctrineHelper.php" helper in: SF_ROOT_DIR\apps\admin\modules/businessunitgroup/lib/helper, SF_ROOT_DIR\apps\admin\lib/helper, SF_ROOT_DIR\lib/helper, SF_SYMFONY_LIB_DIR/helper. The file sfJqueryTreeDoctrineHelper.php exists indeed but not in any previously mentioned folder. The file can only be found in the folder \plugins\sfJqueryTreeDoctrineManagerPlugin\lib\helper. I guess that Symfony doesn't look to that folder while finding helpers? I have tried to move the helper file to one of the previously mentioned folders. As expected, that changes the error. Now I get: 500 | Internal Server Error | sfConfigurationException The component does not exist: "sfJqueryTreeDoctrineManager", "manager". Unfortunately I can't figure out how should I be able to retrieve the "missing" component from the correct folder. I would be very grateful for any advice to help me forward. By the way, I am aware that there are other nested-set / tree plugins available for Symfony (like sfDoctrineTreePlugin and caPropelTreePlugin) but unluckily those are either uncompatible or too limited for my needs.

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• Generic unit test scheduling

  - by Raphink

  Hello, I'm (re)writing a program that does generic unit test scheduling. The current program is a mono-threaded Perl program, but I'm willing to modularize it and parallelize the tests. I'm also considering rewriting it in Python. Here is what I need to do: I have a list of tests, with the following attributes: uri: a URI to test (could be HTTP/HTTPS/SSH/local) ; depends: an associative array of tests/values that this test depends on ; join: a list of DB joints to be added when selecting items to process in this test ; depends_db: additional conditions to add to the DB request when selecting items to process in this test. The program builds a dependency tree, beginning with the tests that have no dependencies ; for each test: a list of items is selected from the database using the conditions (results of depending tests, joints and depends_db) ; the list of items is sent to the URI (using POST or stdin) ; the result is retrived as a YAML file listing the state and comments for the test for each tested item ; the results are stored in the DB ; the test returns, allowing depending tests to be performed. the program generates reports (CSV, DB, graphviz) of the performed tests. The primary use of this program currently is to test a fleet of machines against services such as backup, DNS, etc. The tests can then be: - backup: hosted on the backup machine(s), called through HTTP, checks if the machines' backup went well ; - DNS: hosted on the local machine, called via stdin, checks if the machines' fqdn have a valid DNS entry. Does such a tool/module already exist? What would be the best implementation to achieve this (using Perl or Python)?

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• Syncing two separate structures to the same master data

  - by Mike Burton

  I've got multiple structures to maintain in my application. All link to the same records, and one of them could be considered the "master" in that it reflects actual relationships held in files on disk. The other structures are used to "call out" elements of the main design for purchase and work orders. I'm struggling to come up with a pattern that deals appropriately with changes to the master data. As an example, the following trees might refer to the same data: A |_ B |_ C |_ D |_ E |_ B |_ C |_ D A |_ B E C |_ D A |_ B C D E These secondary structures follow internal rules, but their overall structure is usually user-determined. In all cases (including the master), any element can be used in multiple locations and in multiple trees. When I add a child to any element in the tree, I want to either automatically build the secondary structure for each instance of the "master" element or at least advertise the situation to the user and allow them to manually generate the data required for the secondary trees. Is there any pattern which might apply to this situation? I've been treating it as a view problem, but it turns out to be more complicated than that when you look at the initial generation of the data.

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• Checking inherited attributes in an 'ancestry' based SQL table

  - by Brendon Muir

  I'm using the ancestry gem to help organise my app's tree structure in the database. It basically writes a childs ancestor information to a special column called 'ancestry'. The ancestry column for a particular child might look like '1/34/87' where the parent of this child is 87, and then 87's parent is 34 and 34's is 1. It seems possible that we could select rows from this table each with a subquery that checks all the ancestors to see if a certain attribute it set. E.g. in my app you can hide an item and its children just by setting the parent element's visibility column to 0. I want to be able to find all the items where none of their ancestors are hidden. I tried converting the slashes to comma's with the REPLACE command but IN required a set of comma separated integers rather than one string with comma separated string numbers. It's funny, because I can do this query in two steps, e.g. retrieve the row, then take its ancestry column, split out the id's and make another query that checks that the id is IN that set of id's and that visibility isn't ever 0 and whala! But joining these into one query seems to be quite a task. Much searching has shown a few answers but none really do what I want. SELECT * FROM t1 WHERE id = 99; 99's ancestry column reads '1/34/87' SELECT * FROM t1 WHERE visibility = 0 AND id IN (1,34,87); kind of backwards, but if this returns no rows then the item is visible. Has anyone come across this before and come up with a solution. I don't really want to go the stored procedure route. It's for a rails app.

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