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• How can I create a dynamic LINQ query in C# with possible multiple group by clauses?

  - by FordPrefect141

  I have been a programmer for some years now but I am a newcomer to LINQ and C# so forgive me if my question sounds particularly stupid. I hope someone may be able to point me in the right direction. My task is to come up with the ability to form a dynamic multiple group by linq query within a c# script using a generic list as a source. For example, say I have a list containing multiple items with the following structure: FieldChar1 - character FieldChar2 - character FieldChar3 - character FieldNum1 - numeric FieldNum2 - numeric In a nutshell I want to be able to create a LINQ query that will sum FieldNum1 and FieldNum2 grouped by any one, two or all three of the FieldChar fields that will be decided at runtime depending on the users requirements as well as selecting the FieldChar fields in the same query. I have the dynamic.cs in my project which icludes a GroupByMany extension method but I have to admit I am really not sure how to put these to use. I am able to get the desired results if I use a query with hard-wired group by requests but not dynamically. Apologies for any erroneous nomenclature, I am new to this language but any advice would be most welcome. Many thanks Alex

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• ExecutorService - scaling

  - by Stanciu Alexandru-Marian

  I am trying to write a program in Java using ExecutorService and it's function invokeAll. My question is: does the invokeAll functions solve the tasks simultaneously? I mean, if i have two processors, there will be two workers in the same time? Because a can't make it to scale correct. It takes the same time to complete the problem if i give newFixedThreadPool(2) or 1. List<Future<PartialSolution>> list = new ArrayList<Future<PartialSolution>>(); Collection<Callable<PartialSolution>> tasks = new ArrayList<Callable<PartialSolution>>(); for(PartialSolution ps : wp) { tasks.add(new Map(ps, keyWords)); } list = executor.invokeAll(tasks); Map is a class that implements Callable and wp is a vector of Partial Solutions, a class that holds some informations in different times. Why doesn't it scale? What could be the problem? Thank you, Alex

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• Pros/Cons of MySQL vs Postgresql for production Ruby on Rails environment?

  - by cakeforcerberus

  I will soon be switching from sqlite3 to either postgres or mysql. What should I consider when making this decision? Is mysql more suited for Rails than postgres in some areas and/or vice versa? Or, as I somewhat suspect, does it not really matter either way? Another factor that might play into my decision is the availability of tools to data pump my test data from the sqlite3 db to my new one. Is there anything that ActiveRecord provides natively to do this or any decent plugins/gems to help with this task? BONUS: How do I pronounce "Postgresql" and sound like I know what I'm talking about? :) Thanks Greg Smith for providing the following link that shows the most common pronunciations: http://www.postgresql.org/community/survey.33 UPDATE: Reference this question for more: http://stackoverflow.com/questions/110927/do-you-recommend-postgresql-over-mysql FYI: I ended up using MySQL. There is a neat plugin called yamldb that really saved me some time with the data transfer from my sqlite db to my new mysql one. Instructions on how to install and use it can be found here: http://accidentaltechnologist.com/ruby/change-databases-in-rails-with-yamldb/ Thanks Tom

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• Silverlight - how to render image from non-visible data bound user control?

  - by MagicMax

  Hello! I have such situation - I'd like to build timeline control. So I have UserControl and ItemsControl on it (every row represents some person). The ItemsControl contains another ItemsControl as ItemsControl.ItemTemplate - it shows e.g. events for the person arranged by event's date. So it looks as some kind of grid with dates as a column headers and e.g. peoples as row headers. ........................|.2010.01.01.....2010.01.02.....2010.01.03 Adam Smith....|......[some event#1].....[some event#2]...... John Dow.......|...[some event#3].....[some event#4]......... I can have a lot of persons (ItemsControl #1 - 100-200 items) and a lot of events occured by some day (1-10-30 events per person in one day) the problem is that when user scrolls ItemsControl #1/#2 it happened toooo sloooooowwww due to a lot of elements should be rendered in one time (as I have e.g. a bit of text boxes and other elements in description of particular event) Question #1 - how can I improve it? May be somebody knows better way to build such user control? I have to mention that I'm using custom Virtual panel, based on some custom Virtual panel implementation found somewhere in internet... Question #2 - I'd like to make image with help of WriteableBitmap and render data bound control to image and to show image instead of a lot of elements. Problem is that I'm trying to render invisible data bound control (created in code behind) and it has actualWidth/Height equals to zero (so nothing rendered). How can I solve it? Thank you very much for you help!

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• SQL query using information from 4 tables (not all directly linked)

  - by Yvonne

  I'm developing a simple classroom system, where teachers manage classes and their subjects. I have 2 levels of access in my teachers table, assigned by an integer (1 = admin, 2 = user)... Meaning that the headteacher is the admin :) A teacher (of level 1) can have have many classes and a class can have many teachers (so I have 'TeachersClasses' table). A class can have many subjects, and a teacher can have many subjects. Basically, I'm attempting a query to display the admin teacher's (level 1) subjects. However, only teachers with a level of 2, are directly related to a subject, which is set by the admin user. The headteacher can view all of their subjects via the classroom, but I cannot get all of the subjects to be displayed on one page, instead I can only get the subjects to appear under a specific classroom right now... This is what I have so far, which is returning nothing. (I'm guessing this may require an SQL clause more advanced that 'INNER JOIN' which is the only join type I am familiar with, and thought it would be enough! $query = "SELECT subjects.subjectid, subjects.subjectname, subjects.subjectdetails, classroom.classid, classroom.classname FROM subjects INNER JOIN classroom ON subjects.subjectid = classroom.classid INNER JOIN teacherclasses ON classroom.classid = teacherclasses.classid INNER JOIN teachers ON teacherclasses.teacherid = teachers.teacherid WHERE teachers.teacherid = '".intval( $_SESSION['SESS_TEACHERID'] )."'"; In order for all subjects related to the headteachers class to be displayed, I'm gathering that all of my tables will need to be called up here? Thanks for any help! Example output: subject name: maths // teacher: mr smith // classroom: DG99 x10 for all the subjects associated with the headteachers classrooms :)

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• Python and csv help

  - by user353064

  I'm trying to create this script that will check the computer host name then search a master list for the value to return a corresponding value in the csv file. Then open another file and do a find an replace. I know this should be easy but haven't done so much in python before. Here is what I have so far... masterlist.txt (tab delimited) Name UID Bob-Smith.local bobs Carmen-Jackson.local carmenj David-Kathman.local davidk Jenn-Roberts.local jennr Here is the script that I have created thus far #GET CLIENT HOST NAME import socket host = socket.gethostname() print host #IMPORT MASTER DATA import csv, sys filename = "masterlist.txt" reader = csv.reader(open(filename, "rU")) #PRINT MASTER DATA for row in reader: print row #SEARCH ON HOSTNAME AND RETURN UID #REPLACE VALUE IN FILE WITH UID #import fileinput #for line in fileinput.FileInput("filetoreplace",inplace=1): # line = line.replace("replacethistext","UID") # print line Right now, it's just set to print the master list. I'm not sure if the list needs to be parsed and placed into a dictionary or what. I really need to figure out how to search the first field for the hostname and then return the field in the second column. Thanks in advance for your help, Aaron

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• extjs how to make a nested child using xTemplate when we don't know how deep is it?

  - by Ebo the gordon

  first, sorry if my english bad,.... in my script, variable tplData below is dynamic,... (lets say it generates from database) so, every chid, can have another child. and so on,.... now, i'm stack how to iteration it,.. var tplData = [{ name : 'Naomi White' },{ name : 'Yoko Ono' },{ name : 'John Smith', child : [{ name:'Michael (John\'s son)', child: [{ name : 'Brad (Michael\'s son,John\'s grand son)' },{ name : 'Brid (Michael\'s son,John\'s grand son)', child: [{ name:'Buddy (Brid\'s son,Michael\'s grand son)' }] },{ name : 'Brud (Michael\'s son,John\'s grand son)' }] }] }]; var myTpl = new Ext.XTemplate( '<tpl for=".">', '<div style="background-color: {color}; margin: 10px;">', '<b> Name :</b> {name}<br />', // how to make this over and over every child (while it has ) '<tpl if="typeof child !=\'undefined\'">', '<b> Child : </b>', '<tpl for="child">', '{name} <br />', '</tpl>', '</tpl>', /////////////////////////////////////// '</div>', '</tpl>' ); myTpl.compile(); myTpl.overwrite(document.body, tplData);

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• DAL Layer : EF 4.0 or Normal Data access layer with Stored Procedure

  - by Harryboy

  Hello Experts, Application : I am working on one mid-large size application which will be used as a product, we need to decide on our DAL layer. Application UI is in Silverlight and DAL layer is going to be behind service layer. We are also moving ahead with domain model, so our DB tables and domain classes are not having same structure. So patterns like Data Mapper and Repository will definitely come into picture. I need to design DAL Layer considering below mentioned factors in priority manner Speed of Development with above average performance Maintenance Future support and stability of the technology Performance Limitation : 1) As we need to strictly go ahead with microsoft, we can not use NHibernate or any other ORM except EF 4.0 2) We can use any code generation tool (Should be Open source or very cheap) but it should only generate code in .Net, so there would not be any licensing issue on per copy basis. Questions I read so many articles about EF 4.0, on outset it looks like that it is still lacking in features from NHibernate but it is considerably better then EF 1.0 So, Do you people feel that we should go ahead with EF 4.0 or we should stick to ADO .Net and use any code geneartion tool like code smith or any other you feel best Also i need to answer questions like what time it will take to port application from EF 4.0 to ADO .Net if in future we stuck up with EF 4.0 for some features or we are having serious performance issue. In reverse case if we go ahead and choose ADO .Net then what time it will take to swith to EF 4.0 Lastly..as i was going through the article i found the code only approach (with POCO classes) seems to be best suited for our requirement as switching is really easy from one technology to other. Please share your thoughts on the same and please guide on the above questions

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• Navigating to nodes using xpath in flat structure

  - by James Berry

  I have an xml file in a flat structure. We do not control the format of this xml file, just have to deal with it. I've renamed the fields because they are highly domain specific and don't really make any difference to the problem. <attribute name="Title">Book A</attribute> <attribute name="Code">1</attribute> <attribute name="Author"> <value>James Berry</value> <value>John Smith</value> </attribute> <attribute name="Title">Book B</attribute> <attribute name="Code">2</attribute> <attribute name="Title">Book C</attribute> <attribute name="Code">3</attribute> <attribute name="Author"> <value>James Berry</value> </attribute> Key things to note: the file is not particularly hierarchical. Books are delimited by an occurance of an attribute element with name='Title'. But the name='Author' attribute node is optional. Is there a simple xpath statement I can use to find the authors of book 'n'? It is easy to identify the title of book 'n', but the authors value is optional. And you can't just take the following author because in the case of book 2, this would give the author for book 3. I have written a state machine to parse this as a series of elements, but I can't help thinking there would have been a way to directly get the results that I want.

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• Why my test xml is failing with very simple XSD Schema?

  - by JSteve

  Hi all, I am a bit novice in xml schema. I would be grateful if somebody help me out to understand why my xml is not being validated with the schema: Here is my Schema: <?xml version="1.0" encoding="UTF-8"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.example.org/testSchema" xmlns="http://www.example.org/testSchema"> <xs:element name="Employee"> <xs:complexType> <xs:sequence> <xs:element name="Name"> <xs:complexType> <xs:sequence> <xs:element name="FirstName" /> <xs:element name="LastName" /> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> </xs:element> </xs:schema> Here is my test xml: <?xml version="1.0" encoding="UTF-8"?> <Employee xmlns="http://www.example.org/testSchema"> <Name> <FirstName>John</FirstName> <LastName>Smith</LastName> </Name> </Employee> I am getting following error by Eclipse xml editor/validator: cvc-complex-type.2.4.a: Invalid content was found starting with element 'Name'. One of '{Name}' is expected. I could not understand what is wrong with this schema or my xml.

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• Excel CSV into Nested Dictionary; List Comprehensions

  - by victorhooi

  heya, I have a Excel CSV files with employee records in them. Something like this: mail,first_name,surname,employee_id,manager_id,telephone_number [email protected],john,smith,503422,503423,+65(2)3423-2433 [email protected],george,brown,503097,503098,+65(2)3423-9782 .... I'm using DictReader to put this into a nested dictionary: import csv gd_extract = csv.DictReader(open('filename 20100331 original.csv'), dialect='excel') employees = dict([(row['employee_id'], row) for row in gp_extract]) Is the above the proper way to do it - it does work, but is it the Right Way? Something more efficient? Also, the funny thing is, in IDLE, if I try to print out "employees" at the shell, it seems to cause IDLE to crash (there's approximately 1051 rows). 2. Remove employee_id from inner dict The second issue issue, I'm putting it into a dictionary indexed by employee_id, with the value as a nested dictionary of all the values - however, employee_id is also a key:value inside the nested dictionary, which is a bit redundant? Is there any way to exclude it from the inner dictionary? 3. Manipulate data in comprehension Thirdly, we need do some manipulations to the imported data - for example, all the phone numbers are in the wrong format, so we need to do some regex there. Also, we need to convert manager_id to an actual manager's name, and their email address. Most managers are in the same file, while others are in an external_contractors CSV, which is similar but not quite the same format - I can import that to a separate dict though. Are these two items things that can be done within the single list comprehension, or should I use a for loop? Or does multiple comprehensions work? (sample code would be really awesome here). Or is there a smarter way in Python do it? Cheers, Victor

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• Google App Engine - Caching generated HTML

  - by Alexander

  I have written a Google App Engine application that programatically generates a bunch of HTML code that is really the same output for each user who logs into my system, and I know that this is going to be in-efficient when the code goes into production. So, I am trying to figure out the best way to cache the generated pages. The most probable option is to generate the pages and write them into the database, and then check the time of the database put operation for a given page against the time that the code was last updated. Then, if the code is newer than the last put to the database (for a particular HTML request), new HTML will be generated and served, and cached to the database. If the code is older than the last put to the database, then I will just get the HTML direct from the database and serve it (therefore avoiding all the CPU wastage of generating the HTML). I am not only looking to minimize load times, but to minimize CPU usage. However, one issue that I am having is that I can't figure out how to programatically check when the version of code uploaded to the app engine was updated. I am open to any suggestions on this approach, or other approaches for caching generated html. Note that while memcache could help in this situation, I believe that it is not the final solution since I really only need to re-generate html when the code is updated (as opposed to every time the memcache expires). Kind Regards, and thank you in advance for any suggestions you may be able to offer. -Alex

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• DBD::CSV: Problem with file-name-extensions

  - by sid_com

  In this script I have problems with file-name-extensions: if I use /home/mm/test_x it works, with file named /home/mm/test_x.csv it doesn't: #!/usr/bin/env perl use warnings; use strict; use 5.012; use DBI; my $table_1 = '/home/mm/test_1.csv'; my $table_2 = '/home/mm/test_2.csv'; #$table_1 = '/home/mm/test_1'; #$table_2 = '/home/mm/test_2'; my $dbh = DBI->connect( "DBI:CSV:" ); $dbh->{RaiseError} = 1; $table_1 = $dbh->quote_identifier( $table_1 ); $table_2 = $dbh->quote_identifier( $table_2 ); my $sth = $dbh->prepare( "SELECT a.id, a.name, b.city FROM $table_1 AS a NATURAL JOIN $table_2 AS b" ); $sth->execute; $sth->dump_results; $dbh->disconnect; Output with file-name-extention: DBD::CSV::st execute failed: Execution ERROR: No such column '"/home/mm/test_1.csv".id' called from /usr/local/lib/perl5/site_perl/5.12.0/x86_64-linux/DBD/File.pm at 570. Output without file-name-extension: '1', 'Brown', 'Laramie' '2', 'Smith', 'Watertown' 2 rows Is this a bug?

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• Is there an MVVM-friendly way to swap views without value converters firing unnecessarily?

  - by DanM

  I thought what I was doing was right out of the Josh Smith MVVM handbook, but I seem to be having a lot of problems with value converters firing when no data in the view-model has changed. So, I have a ContentControl defined in XAML like this: <ContentControl Grid.Row="0" Content="{Binding CurrentViewModel}" /> The Window containing this ContentControl references a resource dictionary that looks something like this: <ResourceDictionary ...> <DataTemplate DataType="{x:Type lib_vm:SetupPanelViewModel}"> <lib_v:SetupPanel /> </DataTemplate> <DataTemplate DataType="{x:Type lib_vm:InstructionsPanelViewModel}"> <lib_v:InstructionsPanel /> </DataTemplate> </ResourceDictionary> So, basically, the two data templates specify which view to show with which view-model. This switches the views as expected whenever the CurrentViewModel property on my window's view-model changes, but it also seems to cause value converters on the views to fire even when no data has changed. It's a particular problem with IMultiValueConverter classes, because the values in the value array get set to DependencyProperty.UnsetValue, which causes exceptions unless I specifically check for that. But I'm getting other weird side effects too. This has me wondering if I shouldn't just do everything manually, like this: Instantiate each view. Set the DataContext of each view to the appropriate view-model. Give the ContentControl a name and make it public. Handle the PropertyChanged event for the window. In the event handler, manually set the Content property of the ContentControl to the appropriate view, based the CurrentViewModel (using if statements). This seems to work, but it also seems very inelegant. I'm hoping there's a better way. Could you please advise me the best way to handle view switching so that value converters don't fire unnecessarily?

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• Horizontally align rows in multiple tables using web user control

  - by goku_da_master

  I need to align rows in different tables that are layed out horizontally. I'd prefer to put the html code in a single web user control so I can create as many instances of that control as I want and lay them out horizontally. The problem is, the text in the rows needs to wrap. So some rows may expand vertically and some may not (see the example below). When that happens, the rows in the other tables aren't aligned horizontally. I know I can accomplish all this by using a single table, but that would mean I'd have to duplicate the name, address and phone html code instead of dynamically creating new instances of my user control (in reality there are many more fields than this, but I'm keeping it simple). Is there any way to do this whether with div's, tables or something else? Here's the problem: Mary Jane's address field expands 2 lines, causing her phone field to not align properly with John's and Bob's. Name: John Doe Name: Mary Jane Name: Bob Smith Address: 123 broadway Address: Some really long address Address: Short address Phone: 123-456 that takes up multiple lines Phone: 111-2222 Phone: 456-789 I'm not restricted in any way how to do this (other than using asp.net), but I'd prefer to use a single web control that I instantiate X times at design time (in this example, it's 3 times). I'm using VS2008, and .Net 3.5

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• AssertionFailure: "null identifier" - FluentNH + SQLServerCE

  - by Stefan

  The code fails at session.Save(employee); with AssertionFailure "null identifier". What am I doing wrong? using FluentNHibernate.Cfg; using FluentNHibernate.Cfg.Db; using FluentNHibernate.Mapping; using NHibernate; using NHibernate.Cfg; using NHibernate.Tool.hbm2ddl; namespace FNHTest { public class Employee { public virtual int Id { get; private set; } public virtual string Name { get; set; } public virtual string Surname { get; set; } } public class EmployeeMap : ClassMap { public EmployeeMap() { Id(e = e.Id); Map(e = e.Name); Map(e = e.Surname); } } public class DB { private static ISessionFactory mySessionFactory = null; private static ISessionFactory SessionFactory { get { if (mySessionFactory == null) { mySessionFactory = Fluently.Configure() .Database(MsSqlCeConfiguration.Standard .ConnectionString("Data Source=MyDB.sdf")) .Mappings(m = m.FluentMappings.AddFromAssemblyOf()) .ExposeConfiguration(BuildSchema) .BuildSessionFactory(); } return mySessionFactory; } } private static void BuildSchema(Configuration configuration) { SchemaExport schemaExport = new SchemaExport(configuration); schemaExport.Execute(false, true, false); } public static ISession OpenSession() { return SessionFactory.OpenSession(); } } public class Program { public static void Main(string[] args) { var employee = new Employee { Name = "John", Surname = "Smith" }; using (ISession session = DB.OpenSession()) { session.Save(employee); } } } }

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• How to parse this xml document?

  - by dfjhdfjhdf

  Get such a XML document with the help of ajax (var data = request.responseXML;), how do I parse the contacts?: <?xml version="1.0" encoding="UTF-8"?> <Alladresses xmlns="http://somedomain.org/doc/2007-08-02/"> <Owner> <ID>gut74hfowesdfj49fjsifhryh8e8rta3uyhw4</ID> <Name>Mr.Bin</Name> </Owner> <Contacts> <Person> <Name>Greg</Name> <Phone>3254566756</Phone> </Person> <Person> <Name>Smith</Name> <Phone>342446446</Phone> </Person> <Person> <Name>Yuliya</Name> <Phone>675445566867</Phone> </Person> </Contacts> </Alladresses>

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• c++ passing unknown type to a function and any Class type definition

  - by user259789

  I am trying to create a generic class to write and read Objects to/from file. Called it ActiveRecord class only has one method, which saves the class itself: void ActiveRecord::saveRecord(){ string fileName = "data.dat"; ofstream stream(fileName.c_str(), ios::out); if (!stream) { cerr << "Error opening file: " << fileName << endl; exit(1); } stream.write(reinterpret_cast<const char *> (this), sizeof(ActiveRecord)); stream.close(); } now I'm extending this class with User class: class User : public ActiveRecord { public: User(void); ~User(void); string name; string lastName; }; to create and save the user I would like to do something like: User user = User(); user.name = "John"; user.lastName = "Smith" user.save(); how can I get this ActiveRecord::saveRecord() method to take any object, and class definition so it writes whatever i send it: to look like: void ActiveRecord::saveRecord(foo_instance, FooClass){ string fileName = "data.dat"; ofstream stream(fileName.c_str(), ios::out); if (!stream) { cerr << "Error opening file: " << fileName << endl; exit(1); } stream.write(reinterpret_cast<const char *> (foo_instance), sizeof(FooClass)); stream.close(); } and while we're at it, what is the default Object type in c++. eg. in objective-c it's id in java it's Object in AS3 it's Object what is it in C++??

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• Alternate widgets and logic for ManyToManyField with Django forms

  - by Jaearess

  In my Django project, I have a simple ticket system. When creating a ticket, certain users have the ability to assign the ticket to other users, and to email the ticket to other users as well (this is used as an FYI for those users, so they're aware of the ticket, even though it's not assigned to them.) At the moment, the form for adding a ticket is simply the default Django form, with the "assigned_to" and "email_to" fields being ManyToManyFields, and therefore displayed as MultipleSelect widgets, each with a list of all users. Due to the relatively large number of users, and general awkwardness of the MultipleSelect widget, and alternate layout is now required. The desired layout is a pair of simple Select widgets side-by-side. The first has the option of "Assign to" or "Email to" and the second is a list of the users. Essentially, like this: [Assign to] [John Doe] [Email to] [Jane Roe] [Jack Smith], etc. Of course, since an arbitrary number of users can be assigned or emailed a ticket, there's a simple button that runs some Javascript to add another set of widgets, to allow the user to assign and email as many people as they need to. So far all of that is fairly simple and straight forward. However, the problem I have is using this widget setup/logic setup with Django forms. Instead of lists of users to assign to and email, instead we're getting back pairs of information, one a user and the other which list that user should be placed in. What I'm looking for, but have yet to find, is a way to offload the translation between how the user uses the form, and how Django understands the model to the form itself, so I don't have to manually do the processing of the data before passing it to the form in each place this form is used. Additionally, there's a review screen with the option to go back and change the form before submitting it, so a way to have the form translate both to and from this format would be extremely helpful.

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• Perl - Read XML

  - by chinna_82

  XML <?xml version='1.0'?> <employee> <name>Smith</name> <age>43</age> <sex>M</sex> <department role='manager'>Operations</department> </employee> Perl use XML::Simple; use Data::Dumper; $xml = new XML::Simple; foreach my $data1 ($data = $xml->XMLin("test.xml")) { print Dumper($data1); } Above code managed to all the xml value like this. Output $VAR1 = { 'department' => { 'content' => 'Operations', 'role' => 'manager' }, 'name' => 'John Doe', 'sex' => 'M', 'age' => '43' }; How do I do, if I only want to get the role value. For this example I need to get Role = manager. Any advice or reference link is highly appreciated.

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• How do I stop ValueConverters from firing when swapping the content of a ContentControl

  - by DanM

  I thought what I was doing was right out of the Josh Smith MVVM handbook, but I seem to be having a lot of problems with value converters firing when no data in the view-model has changed. So, I have a ContentControl defined in XAML like this: <ContentControl Grid.Row="0" Content="{Binding CurrentViewModel}" /> The Window containing this ContentControl references a resource dictionary that looks something like this: <ResourceDictionary ...> <DataTemplate DataType="{x:Type lib_vm:SetupPanelViewModel}"> <lib_v:SetupPanel /> </DataTemplate> <DataTemplate DataType="{x:Type lib_vm:InstructionsPanelViewModel}"> <lib_v:InstructionsPanel /> </DataTemplate> </ResourceDictionary> So, basically, the two data templates specify which view to show with which view-model. This switches the views as expected whenever the CurrentViewModel property on my window's view-model changes, but it also seems to cause value converters on the views to fire even when no data has changed. It's a particular problem with IMultiValueConverter classes, because the values in the value array get set to DependencyProperty.UnsetValue, which causes exceptions unless I specifically check for that. But I'm getting other weird side effects too. This has me wondering if I shouldn't just do everything manually, like this: Instantiate each view. Set the DataContext of each view to the appropriate view-model. Give the ContentControl a name and make it public. Handle the PropertyChanged event for the window. In the event handler, manually set the Content property of the ContentControl to the appropriate view, based the CurrentViewModel (using if statements). This seems to work, but it also seems very inelegant. I'm hoping there's a better way. Could you please advise me the best way to handle view switching so that value converters don't fire unnecessarily?

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• Using Constraints on Hierarchical Data in a Self-Referential Table

  - by pbarney

  Suppose you have the following table, intended to represent hierarchical data: +--------+-------------+ | Field | Type | +--------+-------------+ | id | int(10) | | parent | int(10) | | name | varchar(45) | +--------+-------------+ The table is self-referential in that the parent_id refers to id. So you might have the following data: +----+--------+---------------+ | id | parent | name | +----+--------+---------------+ | 1 | 0 | fruit | | 2 | 0 | vegetable | | 3 | 1 | apple | | 4 | 1 | orange | | 5 | 3 | red delicious | | 6 | 3 | granny smith | | 7 | 3 | gala | +----+--------+---------------+ Using MySQL, I am trying to impose a (self-referential) foreign key constraint upon the data to update on cascades and prevent deletion of fruit if they have "children." So I used the following: CREATE TABLE `idtlp_main`.`fruit` ( `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT, `parent` INT(10) UNSIGNED, `name` VARCHAR(45) NOT NULL, PRIMARY KEY (`id`), CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE ON DELETE RESTRICT ) ENGINE = InnoDB; From what I understand, this should fit my requirements. (And parent must default to null to allow insertions, correct?) The problem is, if I change the id of a record, it will not cascade: Cannot delete or update a parent row: a foreign key constraint fails (`iddoc_main`.`fruit`, CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE) What am I missing? Feel free to correct me if my terminology is screwed up... I'm new to constraints.

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• sorting names in a linked list

  - by sil3nt

  Hi there, I'm trying to sort names into alphabetical order inside a linked list but am getting a run time error. what have I done wrong here? #include <iostream> #include <string> using namespace std; struct node{ string name; node *next; }; node *A; void addnode(node *&listpointer,string newname){ node *temp; temp = new node; if (listpointer == NULL){ temp->name = newname; temp->next = listpointer; listpointer = temp; }else{ node *add; add = new node; while (true){ if(listpointer->name > newname){ add->name = newname; add->next = listpointer->next; break; } listpointer = listpointer->next; } } } int main(){ A = NULL; string name1 = "bob"; string name2 = "tod"; string name3 = "thomas"; string name4 = "kate"; string name5 = "alex"; string name6 = "jimmy"; addnode(A,name1); addnode(A,name2); addnode(A,name3); addnode(A,name4); addnode(A,name5); addnode(A,name6); while(true){ if(A == NULL){break;} cout<< "name is: " << A->name << endl; A = A->next; } return 0; }

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• Exception on inserting into Access 2010 in C Sharp

  - by slao.it

  Hello, I am getting this exception when inserting into a Access 2010 database. Ex: System.Data.OleDb.OleDbException (0x80040E14): Syntax error in string in query expression ''CityName ?'. at System.Data.OleDb.OleDbCommand.ExecuteCommandTextErrorHandling(OleDbHResult hr) at System.Data.OleDb.OleDbCommand.ExecuteCommandTextForSingleResult(tagDBPARAMS dbParams, Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteCommandText(Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteCommand(CommandBehavior behavior, Object& executeResult) at System.Data.OleDb.OleDbCommand.ExecuteReaderInternal(CommandBehavior behavior, String method) at System.Data.OleDb.OleDbCommand.ExecuteNonQuery() at ReadingData.Program.Main(String[] args) in C:\Users\user\documents\visual studio 2010\Projects\ReadingData\ReadingData\Program.cs:line 238 INSERT INTO CranbrookMain (ID,BlockNo,Plot,SubPlot,Code,Type,LastName,FirstName,ServiceHome,ServiceAddress,ServiceCity,Notes) VALUES ('1','Y','37','DS','C2','O','SMITH','John','Service Inc.','520B SLATER ROAD N.W.','CityName','CityName ? ') insertSQL = "INSERT INTO CranbrookMain (ID,BlockNo,Plot,SubPlot,Code,Type,LastName," + "FirstName,ServiceHome,ServiceAddress,ServiceCity,Notes) VALUES (" + "'"+id+ "','" + blockNo + "','" + plot + "','" + subPlot + "','" + code + "','" + type + "','" + lastname + "','" + firstname + "','" + serviceHome + "','" + serviceAddress + "','" + serviceCity + "','" + notes +"')"; Console.WriteLine(); OleDbCommand cmd = new OleDbCommand(insertSQL, con); // creating query command cmd.ExecuteNonQuery(); The error occurs in cmd.ExecuteNonQuery() function call. The above SQL INSERT statement works fine if I directly execute in the Access 2010 file.

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• tipfy for Google App Engine: Is it stable? Can auth/session components of tipfy be used with webapp?

  - by cv12

  I am building a web application on Google App Engine that requires users to register with the application and subsequently authenticate with it and maintain sessions. I don't want to force users to have Google accounts. Also, the target audience for the application is the average non-geek, so I'm not very keen on using OpenID or OAuth. I need something simple like: User registers with an e-mail and password, and then can log back in with those credentials. I understand that this approach does not provide the security benefits of Google or OpenID authentication, but I am prepared to trade foolproof security for end-user convenience and hassle-free experience. I explored Django, but decided that consecutive deprecations from appengine-helper to app-engine-patch to django-nonrel may signal that path may be a bit risky in the long-term. I'd like to use a code base that is likely to be maintained consistently. I also explored standalone session/auth packages like gaeutilities and suas. GAEUtilities looked a bit immature (e.g., the code wasn't pythonic in places, in my opinion) and SUAS did not give me a lot of comfort with the cookie-only sessions. I could be wrong with my assessment of these two, so I would appreciate input on those (or others that may serve my objective). Finally, I recently came across tipfy. It appears to be based on Werkzeug and Alex Martelli spoke highly of it here on stackoverflow. I have two primary questions related to tipfy: As a framework, is it as mature as webapp? Is it stable and likely to be maintained for some time? Since my primary interest is the auth/session components, can those components of the tipfy framework be used with webapp, independent of the broader tipfy framework? If yes, I would appreciate a few pointers to how I could go about doing that.

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