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• Error with Drools .brl to .drl rule conversion - Adding dynamic rules

  - by jillika iyer

  Hi, I want to add rules dynamically in drools. What is the main plus point of using KNowledge builder?? Or is it better to just list the Files in the rules directory and add it to my program?? But in this case when I convert from a .brl to .drl file at runtime - my new created .drl is not detected. How can I update the new rule and add it at runtime?? Please help. Thank you J

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• Why does Google Reader use up so much memory?

  - by Ivo

  I'm running the dev version of Chrome and just found out I could see the memory usage of every tab (press shift + ESC to find out yourself). Turns out the Shockwave Flash plugin uses 240 MB of memory and 27% of CPU while having open Google Reader. Killing this page brings it down to 50 MB. I reckon it builts up after reading through about 100 feeds. So my question is: why does it take up so much memory and what should I do to diminish it? Why I care? I often don't restart my browser (or laptop for that matter) and keep the Google Reader tab open for long periods of time. The memory does start to add up that way. Plus I have the feeling, perhaps incorrect, that it slows things down as well looking at the CPU usage. Side note: using Chrome 4 on Windows 7 (32 bit)

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• RadGrid Dynamic CheckBoxList on Edit

  - by Kobojunkie

  I have a situation where I need to, when in Radgrid Edit Mode and user makes a selection on a contained dropdownlist, display a modalPopup containing a Checkboxlist populated with data that relates to dropdownlist selection. When Selections are made on the checkboxlist, and OK button clicked, I want to return to the RadGrid Edit template, and populate a textbox in the template with the checkbox selected information. Anyone have a clear idea of how I ought to handle this. An example will be greatly appreciated please.

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• C# & Adding Dynamic META Tags

  - by Bry4n

  I have this code protected void Page_Load(object sender, EventArgs e) { DataSet.DestinationsDataTable GetDestinations = (DataSet.DestinationsDataTable)dta.GetData(); Page.Title = GetDestinations.Rows[0]["Meta_Title"].ToString(); HtmlMeta hm = new HtmlMeta(); HtmlHead head = (HtmlHead)Page.Header; hm.Name = GetDestinations.Rows[0]["Meta_Desc"].ToString(); hm.Content = GetDestinations.Rows[0]["Meta_Key"].ToString(); head.Controls.Add(hm); } And it's returning this error (on a content page) The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>). Thoughts?

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• Memory leak problem. iPhone SDK

  - by user326375

  Hello, i've got a problem, i cannot solve it, just recieving error: Program received signal: “0”. The Debugger has exited due to signal 10 (SIGBUS).The Debugger has exited due to signal 10 (SIGBUS). Here is some method, if i comment it out, problem goes aways - (void)loadTexture { const int num_tex = 10; glGenTextures(num_tex, &textures[0]); //TEXTURE #1 textureImage[0] = [UIImage imageNamed:@"wonder.jpg"].CGImage; //TEXTURE #2 textureImage[1] = [UIImage imageNamed:@"wonder.jpg"].CGImage; //TEXTURE #3 textureImage[2] = [UIImage imageNamed:@"wall_eyes.jpg"].CGImage; //TEXTURE #4 textureImage[3] = [UIImage imageNamed:@"wall.jpg"].CGImage; //TEXTURE #5 textureImage[4] = [UIImage imageNamed:@"books.jpg"].CGImage; //TEXTURE #6 textureImage[5] = [UIImage imageNamed:@"bush.jpg"].CGImage; //TEXTURE #7 textureImage[6] = [UIImage imageNamed:@"mushroom.jpg"].CGImage; //TEXTURE #8 textureImage[7] = [UIImage imageNamed:@"roots.jpg"].CGImage; //TEXTURE #9 textureImage[8] = [UIImage imageNamed:@"roots.jpg"].CGImage; //TEXTURE #10 textureImage[9] = [UIImage imageNamed:@"clean.jpg"].CGImage; for(int i=0; i<num_tex; i++) { NSInteger texWidth = CGImageGetWidth(textureImage[i]); NSInteger texHeight = CGImageGetHeight(textureImage[i]); GLubyte *textureData = (GLubyte *)malloc(texWidth * texHeight * 4); CGContextRef textureContext = CGBitmapContextCreate(textureData, texWidth, texHeight, 8, texWidth * 4, CGImageGetColorSpace(textureImage[i]), kCGImageAlphaPremultipliedLast); CGContextDrawImage(textureContext, CGRectMake(0.0, 0.0, (float)texWidth, (float)texHeight), textureImage[i]); CGContextRelease(textureContext); glBindTexture(GL_TEXTURE_2D, textures[i]); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texWidth, texHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); free(textureData); } } anyone can help me with releasing/deleting objects in this method? Thanks.

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• In-Memory SQL-CE

  - by harley.333

  Is there a way to connect to a SQL-CE database as a stream? Specifically, our ASP.Net application builds small SDF at runtime for off-line needs. When the user is done with his off-line duties, he uploads the SDF and the application imports the new and updated data. No problems there. Currently, we're saving the uploaded SDF to the web-server's hard-drive and connecting to the file. Can we connect to the uploaded SDF without saving it to the hard-drive? We are using the DbProviderFactory.CreateConnection method, but we're open to suggestions.

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• Rails Multiple Checkboxes with Javascript Dynamic Select

  - by Jack

  Hi, I have followed the Railscast episode 88 to implement a set of dependant drop down menus. In the students-new view, when the student's year is selected, the javascript figures out which courses are available to that year and offers the selection in a new drop down menu. My javascript erb file is here: var courses = new Array(); <% for course in @courses -%> <%for year in course.years -%> courses.push(new Array(<%= year.year_id%>, '<%=h course.title%>', <%= course.id%>)); <%end -%> <% end -%> function yearSelected() { year_id = $('student_year_id').getValue(); options = $('student_course_ids').options; options.length = 1; courses.each(function(course) { if (course[0] == year_id) { options[options.length] = new Option(course[1], course[2]); } }); if (options.length == 1) { $('course_field').hide(); } else { $('course_field').show(); } } document.observe('dom:loaded', function() { yearSelected(); $('student_year_id').observe('change', yearSelected); }); Any my view is as follows: <% form_for(@student) do |f| %> <%= f.error_messages %> <p> <%= f.label :name %><br /> <%= f.text_field :name %> </p> <p> <%= f.label :cid, "CID" %><br /> <%= f.text_field :cid %> </p> <p> <label for="student_year_id">Year:</label> <%= collection_select(:student, :year_id, Year.all, :id, :title, {:prompt => true})%> </p> <p id="course_field"> <label for="student_course_ids">Course:</label> <%= collection_select(:student, :course_ids, Course.find(:all), :id, :title, {:prompt => true}, {:multiple => true})%> </p> <p> <%= f.submit 'Save' %> </p> <% end %> What I would like to do is to add checkboxes instead of the drop down menu. Any suggestions? I previously was using this method, but was not able to get it to work with the new javascript. Cheers

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• How can I use Apache to reverse proxy a dynamic url

  - by backplane

  I want a user to be able to load a url in their browser, but not get redirected: http://example.com/abc/{var1}/{var2}/def I want the example.com apache 2.2 server to take that request, and "invisibly" and without redirect reverse proxy it to: http://other.example.com/abc/{var1}/{var2}/def I have spent hours trying different combinations of RewriteRule, ProxyPass, ProxyPassMatch, and ProxyPassReverse, all to no avail. Here is my current attempt, which seems to do a redirect to /test instead of an invisible proxy. RewriteRule ^/abc/([^/\.]+)/([^/\.]+)/def/?$ /test/abc/$1/$2/def [P] ProxyPass /test http://other.example.com/ ProxyPassReverse /test http://other.example.com/

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• ActionScript instanceof for dynamic interface

  - by Bart van Heukelom

  interface If { ... } class Impl implements If { ... } function test(type:Class, obj) { return obj instanceof type; } test(If, new Impl()); // returns false. why, and how to do it right?

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• Multiple dynamic timers

  - by Rickard

  I am working on a project where I need to let the user create one (or more) timers to fire off an event. The user is supposed to define variables such as if the timer should be active and how often the timer will fire along with some other variables of what will happen when the timer is fiering. All these variables are stored in a dictionary (Disctionary) where the object holds all the variables the user has set and the string is the name that the user has chosen for this timer. I then want my program to loop through this dictionary and search for all objects which has the variable t_Active set to true (this I have already achieved). What I need help with figuring out is the follwoing: When it detects the variable, and if it's set to true, I need the program to see if there is already a timer created for this. If it isn't, it should create one and set the relevant parameters for the timer. The two variables t_num and t_period should decide the interval of the timer. t_num is an int and t_period is a string which will be set to either minutes, hours or days. Combining t_num with 60000 (minutes), 3600000 (hours) or 86400000 should give the corrct interval. But how would I go on about programatically create a timer for each user-defined active object? And how do I get the program to detect wether or not a timer has already been created? I have been searching both here and on google, but so far I haven't come across something that makes sense to me. I am still learning C#, so what make sense to you guys may not neccessarilly make sense to me yet. :) I hope I have explaned what I need good enough, please do ask me to clarify if you don't get me. Edit: Maybe I should also mention that the mentioned dictionary will also be saved to an XML file to that the user can pick up all the settings they made at any time.

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• Read vector into CUDA shared memory

  - by Ben

  I am new to CUDA and programming GPUs. I need each thread in my block to use a vector of length ndim. So I thought I might do something like this: extern __shared__ float* smem[]; ... if (threadIddx.x == 0) { for (int d=0; d<ndim; ++d) { smem[d] = vector[d]; } } __syncthreads(); ... This works fine. However, I seems wasteful that a single thread should do all loading, so I changed the code to if (threadIdx.x < ndim) { smem[threadIdx.x] = vector[threadIdx.x]; } __syncthreads(); which does not work. Why? It gives different results than the above code even when ndim << blockDim.x.

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• Creating a dynamic (video) Overlay on Google Maps on Android 2.1

  - by Soumya

  I'm trying to create a map overlay for displaying a video stream (MJPEG) on top of a Mapview. Currently I've a standalone activity that creates a data thread for fetching MJPEG video frames. I'm using a handler to send a frame (as a Bitmap) from the data thread to the main activity which then updates the UI. I'm not sure how I can implement "refresh" for updating my "overlayed" video stream. EDIT: What I mean by "refresh" is - how can I update the video portion (not the mapview) of my UI whenever I get a new video frame. I plan to paint the video frame (bitmap) in the "draw method" of my implementation of the Overlay subclass. But the "draw" method is not invoked by me directly. Thanks.

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• dynamic date formats in eyecon's Bootstrap Datepicker

  - by Jennifer Michelle

  I need to update my datepickers' date format (mm.dd.yyyy etc) using a select box. I am currently using Eyecon's Bootstrap Datepicker because it had the smallest files size that I could find (8k minified), and includes the date formats I need. I also tried to trigger date format changes in several other datepickers without any success. Fiddle: http://jsfiddle.net/Yshy7/8/ Is there an obvious way to trigger a change from the select box to the datepickers? //date format var dateFormat = $('#custom_date_format').val() || "mm/dd/yyyy"; $('#custom_date_format').change(function() { var dateFormat = $(this).val(); }); //start and end dates var nowTemp = new Date(); var now = new Date(nowTemp.getFullYear(), nowTemp.getMonth(), nowTemp.getDate(), 0, 0, 0, 0); var checkin = $('.j-start-date').datepicker({ format: dateFormat, onRender: function(date) { //return date.valueOf() < now.valueOf() ? 'disabled' : ''; } }).on('changeDate', function(ev) { if (ev.date.valueOf() > checkout.date.valueOf()) { var newDate = new Date(ev.date) newDate.setDate(newDate.getDate()); checkout.setValue(newDate); } checkin.hide(); $('.j-end-date')[0].focus(); }).data('datepicker'); var checkout = $('.j-end-date').datepicker({ format: dateFormat, onRender: function(date) { return date.valueOf() <= checkin.date.valueOf() ? 'disabled' : ''; } }).on('changeDate', function(ev) { checkout.hide(); }).data('datepicker');

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• Dynamic Column that contains a Repeater

  - by djbyter

  How would I go about doing this programatically? I can do this just fine declaratively, using a template column and then using something like this: ... <TemplateGridColumn> <ItemTemplate> <div> <asp:Image ID="groupImg" CssClass="groupImg" runat="server"/> <asp:Repeater ID="groupItemRpt" runat="server"> <HeaderTemplate> <ul class="groupItemList"> </HeaderTemplate> <ItemTemplate> <li> <asp:Image ID="itemImg" runat="server" /> <asp:HiddenField ID="itemValue" runat="server" /> </li> </ItemTemplate> <FooterTemplate> </ul> </FooterTemplate> </asp:Repeater> </div> </ItemTemplate> </TemplateGridColumn> ... I am dynamically creating this grid based on the data, so I'm already added columns with one set of controls. But now I need to figure out how to show multiple images, which expand/contract if the groupImg image control is clicked (i just toggle the ul) .. Can anyone point me in the right direction? Thanks.

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• Issues with dynamic <title> in PHP

  - by dotman14

  I have the code below: <?php $title = "Result Computation" ; ?> <title> <?php echo $title ; ?> </title> I'm using includes to call the header on all the pages, but what i want to do is that on every page i want to make it generate a specific title. On each page i've added $title = "Page Title" ; So that when the page loads it gets the title from the $title i've set on that page, but it the pages keep getting the default Title. Please how do i solve this? Thanks for your time.

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• dynamic char array sizing

  - by droseman

  Hello, In my application, I have a char array defined which can take one of three options: "okay", "high", "low" which are then sent down a serial port to a remote device. I currently have the array sized to take the 4 character words plus carriage return and line feed, but when I have to send "low" I get a null character in the strings, which I am concerned would confuse the host terminal. array definition char mod1_status_char[6] = {'0','0','0','0','0','0'}; char mod2_status_char[6] = {'0','0','0','0','0','0'}; char mod3_status_char[6] = {'0','0','0','0','0','0'}; sample of switch case statement: void DCOKStatus(uint8_t *ptr_status) { uint8_t status = *ptr_status; switch (status) { case 0x00: strcpy(mod1_status_char, "okay"); strcpy(mod2_status_char, "okay"); strcpy(mod3_status_char, "okay"); break; case 0x10: strcpy(mod1_status_char, "okay"); strcpy(mod2_status_char, "okay"); strcpy(mod3_status_char, "low"); break; } This is the struct which makes the message string to send strcpy(MsgStatus_on.descriptor_msg, "$psu_"); MsgStatus_on.address01 = hex_addr[0]; MsgStatus_on.address02 = hex_addr[1]; MsgStatus_on.space01 = 0x20; strcpy(MsgStatus_on.cmdmsg01, "op_en op1_"); strcpy(MsgStatus_on.statusmsg01, mod1_status_char); MsgStatus_on.space02 = 0x20; strcpy(MsgStatus_on.cmdmsg02, "op2_"); strcpy(MsgStatus_on.statusmsg02, mod2_status_char); MsgStatus_on.space03 = 0x20; strcpy(MsgStatus_on.cmdmsg03, "op3_"); strcpy(MsgStatus_on.statusmsg03, mod3_status_char); MsgStatus_on.CR = 0x0D; MsgStatus_on.LF = 0x0A; and this sends the message void USARTWrite(char *object, uint32_t size) { GPIO_SetBits(GPIOB, GPIO_Pin_1); char *byte; for (byte = object; size--; ++byte) { USART_SendData(USART1,*byte); } Would anyone be able to suggest a good approach to dynamically size the array to one character shorter when I need to send "low"? Thanks

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• Redis, it's memory limit and persistance question?

  - by Kirzilla

  Hello, I'm rather new to Redis and before using it I'd like to learn some important (as for me) details on it. So.... Redis is using RAM and HDD for storing data. RAM is used as fast read/write storage, HDD is used to make this data persistant. When Redis is started it loads all data from HDD to RAM or it loads only often queried data to the RAM? What if I have 500Mb Redis storage on HDD, but I have only 100Mb or RAM for Redis. Where can I read about it? Thank you PS: Sorry for my English

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• Problems with generation of dynamic code

  - by user308344

  This code gif an exception: Invocation exception, please help, I don't know what happen, I think is some thing with the Add because he work when I push onto the stack intergers, and when i push lvalue It's didn't work, thanks static void Main(string[] args) { AppDomain dominioAplicacion = System.Threading.Thread.GetDomain(); AssemblyName nombre_Del_Ensamblado = new AssemblyName("ASS"); AssemblyBuilder ensambladoBld = dominioAplicacion.DefineDynamicAssembly(nombre_Del_Ensamblado, AssemblyBuilderAccess.RunAndSave); ModuleBuilder moduloBld = ensambladoBld.DefineDynamicModule("<MOD"); TypeBuilder claseContenedoraBld = moduloBld.DefineType("claseContenedora"); MethodBuilder mainBld = claseContenedoraBld.DefineMethod("main", MethodAttributes.Public | MethodAttributes.Static, typeof(void), Type.EmptyTypes); ILGenerator il = mainBld.GetILGenerator(); FieldBuilder campoBld = claseContenedoraBld.DefineField("x", typeof(int), FieldAttributes.Public | FieldAttributes.Static); il.Emit(OpCodes.Ldc_I4, 2); il.Emit(OpCodes.Stsfld, campoBld); FieldBuilder campoBld1 = claseContenedoraBld.DefineField("x1", typeof(int), FieldAttributes.Public | FieldAttributes.Static); il.Emit(OpCodes.Ldc_I4, 2); il.Emit(OpCodes.Stsfld, campoBld1); il.Emit(OpCodes.Ldftn, campoBld); //il.Emit(OpCodes.Unbox, typeof(int)); //il.Emit(OpCodes.Stloc_0); il.Emit(OpCodes.Ldloc_0); il.Emit(OpCodes.Ldftn, campoBld1); //il.Emit(OpCodes.Unbox, typeof(int)); il.Emit(OpCodes.Stloc_1); il.Emit(OpCodes.Ldloc_1); //il.Emit(OpCodes.Box, typeof(int)); //il.Emit(OpCodes.Ldftn, campoBld1); //il.Emit(OpCodes.Unbox, typeof(int)); il.Emit(OpCodes.Add); il.Emit(OpCodes.Pop); //il.Emit(OpCodes.Stsfld, campoBld1); il.Emit(OpCodes.Ret); Type t = claseContenedoraBld.CreateType(); object ptInstance = Activator.CreateInstance(t, new Type[] { }); t.InvokeMember("main", BindingFlags.InvokeMethod | BindingFlags.Static | BindingFlags.Public, null, ptInstance, new object[0]); var x = t.GetField("x"); }

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• Memory over-release problem when I am animating UIView

  - by Sheehan Alam

  I have enabled NSZombie's and I am getting the following message in my console when I am running my application: *** -[UIViewAnimationState release]: message sent to deallocated instance 0xf96d7e0 Here is the method that is performing the animation -(void)loadAvatar:(STObject*)st { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; avatar.alpha = 0; avatar.frame = avatarRectSmall; avatar.image = [ImageCache getMemoryCachedImageAtUrl:st.avatar_url]; [UIView beginAnimations:nil context:nil]; [UIView setAnimationDuration:.50]; avatar.frame = avatarRectNormal; [avatar setAlpha:1]; [UIView commitAnimations]; [pool release]; pool = nil; } I don't always get a crash, only sometimes. I'm wondering what is getting released?

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• Localizing concatenated or dynamic strings

  - by SooDesuNe

  I'm familiar with using NSLocalizedString() to localize strings, but the problem I have today requires a little more finesse. My situation is like this: NSString *userName; //the users name, entered by the user. Does not need localized NSString *favoriteFood; //the users favorite food, also entered by user, and not needing localized NSString *summary = [NSString stringWithFormat:@"%@'s favorite food is %@", userName, favoriteFood]; This works fine for english, but not every language uses the same word ordering as English, for example, a word-by-word translation of the same sentance from Japanese into English would read: UserName's favorite food pizza is Not to mention that 's is doesn't make a possessive in every language. What techniques are available for localizing this type of concatenated sentence?

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• Lexical and dynamic scoping in Mathematica: Local variables with Module, With, and Block

  - by dreeves

  The following code returns 14 as you'd expect: Block[{expr}, expr = 2 z; f[z_] = expr; f[7]] But if you change that Block to a Module then it returns 2*z. It seems to not matter what other variables besides expr you localize. I thought I understood Module, Block, and With in Mathematica but I can't explain the difference in behavior between Module and Block in this example. Related resources: Tutorial on Modularity and the Naming of Things from the Mathematica documentation Excerpt from a book by Paul R. Wellin, Richard J. Gaylord, and Samuel N. Kamin Explanation from Dave Withoff on the Mathematica newsgroup

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• Dynamic Midi generation and playback on Android: Possible?

  - by Peterdk

  Strangely I find no support for Midi in Android. The only thing that comes close is the Jetplayer, but this only takes a existing .jet file. I want to dynamically generate a midi file with some intervals and play it. I even thought about just manually creating a .jet file with a tone and then transposing it with the jet player, but it limits the transposing to -12, +12. Which is not so good for me. There also is a ToneGenerator on Android, but it's limited to predefined tones with no way to transpose. Does someone know how to achieve midi generation and playback on Android?

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• Single Form with Multiple Dynamic Buttons

  - by John Reilly

  I've spent hours/days trying to figure this out and now I'm completely perplexed so I thought I'd give stackoverflow a try. I'm (a newb) working in Java/JSP using Eclipse hosting on Google App Engine trying to develop an app for a volunteer organization I'm a member of. Rather than embarrass myself by showing my current code I'd love just a nudge in the right direction. I have a form (which doubles as a report basically) showing "people" grouped under the "task" they are currently working on. I would like to select multiple people from multiple tasks and reassign them to another task e.g. Bill and Jane are Gardening, Jeff is Painting. I want to select Jane and Jeff (all people have an associated checkbox in the form) and re-assign them to Sweeping (which is a task on the form but has no people assigned to it yet). Ideally, the re-assignment to Sweeping would be via a Sweeping button (each task would have a dynamically-created task button) that would pass the "Sweeping" value to a servlet along with an array or list of people whose checkbox has been checked. The servlet would handle the request (creating an Assignment "object/entity" with timeStamp, personId, taskId) and then re-direct back to the form/report which would then repaint with the current tasks/people generated from the Assignments class in the datastore. All the tasks are user-defined and retrieved from the database when building the form. Ditto the people. I've been trying to keep the jsp for presentation and the servlets for the processing but I'm no purist and would just like to get unstuck. Many thanks in advance for your assistance.

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• JQuery - Adding Cells to Dynamic Tree Table

  - by BPotocki

  I can't quite wrap my head around this one... A table like the one below is spit out by a renderer from some XML. The XML it comes from has a variable depth. (Please point out if I'm using the rowspans in a horrific manner as well, I just came to this table with some experimentation). <table border="1"> <tr> <td rowspan="12">> 1</td> </tr> <tr> <td rowspan="3">1 > 2</td> </tr> <tr> <td>1 > 2 > 5</td> </tr> <tr> <td>1 > 2 > 6</td> </tr> <tr> <td rowspan="3">1 > 3</td> </tr> <tr> <td>1 > 3 > 7</td> </tr> <tr> <td>1 > 3 > 8</td> </tr> <tr> <td rowspan="3">1 > 4</td> </tr> <tr> <td>1 > 4 > 9</td> </tr> <tr> <td>1 > 4 > 10</td> </tr> </table> What I'm trying to accomplish in JQuery is this... User clicks cell "1 2" (which will have an ID). An item is dynamically added to the third level, but UNDER "1 2 6". What I could do is just add another row underneath "1 2" and increase the rowspan from "1 2", but the new cell would then appear out of order amongst "1 2 5" and "1 2 6". I don't really need the exact code to do this, just something to stop my head from spinning around this...Thanks!

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• Dynamic model choice field in django formset using multiple select elements

  - by Aryeh Leib Taurog

  I posted this question on the django-users list, but haven't had a reply there yet. I have models that look something like this: class ProductGroup(models.Model): name = models.CharField(max_length=10, primary_key=True) def __unicode__(self): return self.name class ProductRun(models.Model): date = models.DateField(primary_key=True) def __unicode__(self): return self.date.isoformat() class CatalogItem(models.Model): cid = models.CharField(max_length=25, primary_key=True) group = models.ForeignKey(ProductGroup) run = models.ForeignKey(ProductRun) pnumber = models.IntegerField() def __unicode__(self): return self.cid class Meta: unique_together = ('group', 'run', 'pnumber') class Transaction(models.Model): timestamp = models.DateTimeField() user = models.ForeignKey(User) item = models.ForeignKey(CatalogItem) quantity = models.IntegerField() price = models.FloatField() Let's say there are about 10 ProductGroups and 10-20 relevant ProductRuns at any given time. Each group has 20-200 distinct product numbers (pnumber), so there are at least a few thousand CatalogItems. I am working on formsets for the Transaction model. Instead of a single select menu with the several thousand CatalogItems for the ForeignKey field, I want to substitute three drop-down menus, for group, run, and pnumber, which uniquely identify the CatalogItem. I'd also like to limit the choices in the second two drop-downs to those runs and pnumbers which are available for the currently selected product group (I can update them via AJAX if the user changes the product group, but it's important that the initial page load as described without relying on AJAX). What's the best way to do this? As a point of departure, here's what I've tried/considered so far: My first approach was to exclude the item foreign key field from the form, add the substitute dropdowns by overriding the add_fields method of the formset, and then extract the data and populate the fields manually on the model instances before saving them. It's straightforward and pretty simple, but it's not very reusable and I don't think it is the right way to do this. My second approach was to create a new field which inherits both MultiValueField and ModelChoiceField, and a corresponding MultiWidget subclass. This seems like the right approach. As Malcolm Tredinnick put it in a django-users discussion, "the 'smarts' of a field lie in the Field class." The problem I'm having is when/where to fetch the lists of choices from the db. The code I have now does it in the Field's __init__, but that means I have to know which ProductGroup I'm dealing with before I can even define the Form class, since I have to instantiate the Field when I define the form. So I have a factory function which I call at the last minute from my view--after I know what CatalogItems I have and which product group they're in--to create form/formset classes and instantiate them. It works, but I wonder if there's a better way. After all, the field should be able to determine the correct choices much later on, once it knows its current value. Another problem is that my implementation limits the entire formset to transactions relating to (CatalogItems from) a single ProductGroup. A third possibility I'm entertaining is to put it all in the Widget class. Once I have the related model instance, or the cid, or whatever the widget is given, I can get the ProductGroup and construct the drop-downs. This would solve the issues with my second approach, but doesn't seem like the right approach.

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