explain - Page 230 - Developer IT

What is the purpose of the Html "no-js" class?

- by Swader

I notice that in a lot of template engines, in the HTML5 Boilerplate, in various frameworks and in plain php sites there is the no-js class added onto the html element. Why is this done? Is there some sort of default browser behavior that reacts to this class? Why include it always? Does that not render the class itself obsolete, if there is no no-"no-js" case and html can be addressed directly? Here is an example from the HTML5 Boilerplate index.html:      <html lang="en" class="no-js">  As you can see, the html element will always have this class. Can someone explain why this is done so often?

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Help with MySQL query... Need help ordering a group of rows

- by user156814

I can tell it best by explaining the query I have, and what I need. I need to be able to get a group of items from the database, grouped by category, manufacturer, and year made. The groupings need to be sorted based on total amount of items within the group. This part is done with the query below. Secondly, I need to be able to show an image of the most expensive item out of the group, which is why I use MAX(items.current_price). I thought MAX() gets the ENTIRE row corresponding to the largest column value. I was wrong, as MAX only gets the numeric value of the largest price. So the query doesnt work well for that. SELECT items.id, items.year, items.manufacturer, COUNT(items.id) AS total, MAX(items.current_price) AS price, items.gallery_url, FROM ebay AS items WHERE items.primary_category_id = 213 AND items.year <> '' AND items.manufacturer <> '' AND items.bad_item <> 1 GROUP BY items.primary_category_id, items.manufacturer, items.year ORDER BY total DESC, price ASC LIMIT 10 if that doesnt explain it well, the results should be something like this id 10548 year 1989 manufacturer bowman total 451 price 8500.00 (The price of the most expensive item in the table/ not the price of item 10548) gallery_url http://ebay.xxxxx (The image of item 10548) A little help please. Thanks

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How do virtual destructors work?

- by Prabhu

Few hours back I was fiddling with a Memory Leak issue and it turned out that I really got some basic stuff about virtual destructors wrong! Let me put explain my class design. class Base { virtual push_elements() {} }; class Derived:public Base { vector<int> x; public: void push_elements(){ for(int i=0;i <5;i++) x.push_back(i); } }; void main() { Base* b = new Derived(); b->push_elements(); delete b; } The bounds checker tool reported a memory leak in the derived class vector. And I figured out that the destructor is not virtual and the derived class destructor is not called. And it surprisingly got fixed when I made the destructor virtual. Isn't the vector deallocated automatically even if the derived class destructor is not called? Is that a quirk in BoundsChecker tool or is my understanding of virtual destructor wrong?

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Why is Func<T> ambiguous with Func<IEnumerable<T>>?

- by Matt Hamilton

This one's got me flummoxed, so I thought I'd ask here in the hope that a C# guru can explain it to me. Why does this code generate an error? class Program { static void Main(string[] args) { Foo(X); // the error is on this line } static String X() { return "Test"; } static void Foo(Func<IEnumerable<String>> x) { } static void Foo(Func<String> x) { } } The error in question: Error 1 The call is ambiguous between the following methods or properties: 'ConsoleApplication1.Program.Foo(System.Func<System.Collections.Generic.IEnumerable<string>>)' and 'ConsoleApplication1.Program.Foo(System.Func<string>)' C:\Users\mabster\AppData\Local\Temporary Projects\ConsoleApplication1\Program.cs 12 13 ConsoleApplication1 It doesn't matter what type I use - if you replace the "String" declarations with "int" in that code you'll get the same sort of error. It's like the compiler can't tell the difference between Func<T> and Func<IEnumerable<T>>. Can someone shed some light on this?

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Validation problem with a 'JotForm' template

- by Thomas

A client sent me a form template they had created using jotform.com to implement on their wordpress site. The form template is supposed to hide part of the form until the user clicks the 'next' button. At which point a script is supposed to validate all of the input fields the user has presumably filled out and then display the rest of the form. While I have successfully managed to get the form to display the next part of the form when the user clicks 'next', it fails to validate the input fields. Its kind of difficult to explain without a huge block of text so it is probably easier to show you: The original working template that the customer sent me: http://www.loftist.com/jotform/List_Your_Loft.html The problem child: http://www.loftist.com/?page_id=78 If you just click on one of the input fields and then click elsewhere on the page, the input fields successfully return a validation error message and prevent the user from clicking on the 'next' button. However, if you simply click on the next button than the next set of fields get displayed. Any thoughts? What am I doing wrong here? Im convinced this must be a really simple problem but Im not sure what it could be....

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Telerik chart not loading correctly in new window (ajax issue?)

- by Phillip Schmidt

I have a page which contains user controls with Telerik Charts (grids also, but they work fine). From this page, the user can click on a button to be redirected to a "Printer-Friendly Version" type page, which opens a new window via javascript and goes through a slightly different view (for formatting and stuff), but the telerik code is all the same. The problem is, my Chart displays just fine in the original window, but the new window displays basically an empty chart with no data. This bug is only present in IE, and only applies to Charts. Grids work fine, for whatever reason. I'm thinking this is due to differences in script caching between browsers -- correct me if I'm wrong, I'm semi-new to client-directed web development. Anyway I read somewhere that Telerik has issues with loading data and/or js files when loaded via ajax, so maybe that's the problem? If so, how could I get around this? And if not, any ideas on what could be causing this issue? It's causing me a great deal of frustration, since a print preview page seems like it should be the easiest of jobs. Edit: The charts are being rendered as html (if somebody can explain how to render them as images, that would be awesome). And dev tools shows basically the same thing between chrome and IE. Whenever my web service goes back up ill WinMerge them and look for any peculiarities/differences between them. In the mean time, though, the "render as an image" concept sounds promising. That way I could just save the image from the first page, and insert it right into the print preview page, right?. And since it's a print-preview page, it's not going to need to be interactive or anything, so that'd work out nicely. Another (important) Edit: These are probably the culprit... And here is a little more detail on that: And here is a side-by-side of it working(in chrome) and not working (in IE):

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JQuery: how to store records id for data from ajax query in dynamicly created html elements

- by grapkulec

Probably question title is rather cryptic but I will try to explain myself here so please bare with me :) Let's assume this configuration: server-side is PHP application responding for requests with data (list of items, single item details, etc.) in json format client-side is JQuery application sending ajax request to that PHP app and creating html content corresponding with received data So, for example: client requests "list of all animals with names staring with 'A'", gets the json response from server, and for every "animal" creates some html gizmo like div with animal description or something like that. It doesn't really matter what html element it will be but it has to point exactly to specific record by "containing" id of that record. And here is my dilemma: is it good solution to use "id" property for that? So it would be like: <div id="10" class="animal"> <p> This is animal of very mysterious kind... </p> </div> <div id="11" class="animal"> <p> And this one is very common to our country... </p> </div> where id="10" is of course indication that this is representation of record with id = 10. Or maybe I should store this record id in some custom made tag like <record_id>10</record_id> and leave an "id" strictly for what it was meant to be (css selector)? I need that record id for further stuff like updating database with some user input or deleting some of "animals" or creating new ones or anything that will be needed. All manipulations will be done with JQuery and ajax requests and responses will be visualized also with dynamic creation of html interface. I'm sure that somebody had to deal with that kind of stuff before so I would be grateful for some tips on that topic.

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Java Matcher groups: Understanding The difference between "(?:X|Y)" and "(?:X)|(?:Y)"

- by user358795

Can anyone explain: Why the two patterns used below give different results? (answered below) Why the 2nd example gives a group count of 1 but says the start and end of group 1 is -1? public void testGroups() throws Exception { String TEST_STRING = "After Yes is group 1 End"; { Pattern p; Matcher m; String pattern="(?:Yes|No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } { Pattern p; Matcher m; String pattern="(?:Yes)|(?:No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } } Which gives the following output: Pattern=(?:Yes|No)(.*)End Found=true Group count=1 Start of group 1=9 End of group 1=21 Pattern=(?:Yes)|(?:No)(.*)End Found=true Group count=1 Start of group 1=-1 End of group 1=-1

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Doubly Linked Lists Implementation

- by user552127

Hi All, I have looked at most threads here about Doubly linked lists but still unclear about the following. I am practicing the Goodrich and Tamassia book in Java. About doubly linked lists, please correct me if I am wrong, it is different from a singly linked list in that a node could be inserted anywhere, not just after the head or after the tail using both the next and prev nodes available, while in singly linked lists, this insertion anywhere in the list is not possible ? If one wants to insert a node in a doubly linked list, then the default argument should be either the node after the to-be inserted node or node before the to-be inserted node ? But if this is so, then I don't understand how to pass the node before or after. Should we be displaying all nodes that were inserted till now and ask the user to select the node before or after which some new node is to be inserted ? My doubt is how to pass this default node. Because I assume that will require the next and prev nodes of these nodes as well. For e.g, Head<-A<-B<-C<-D<-E<-tail If Z is the new node to be inserted after say D, then how should node D be passed ? I am confused with this though it seems pretty simple to most. But pl do explain. Thanks, Sanjay

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How to calculate the normal of points on a 3D cubic Bézier curve given normals for its start and end points?

- by Robert

I'm trying to render a "3D ribbon" using a single 3D cubic Bézier curve to describe it (the width of the ribbon is some constant). The first and last control points have a normal vector associated with them (which are always perpendicular to the tangents at those points, and describe the surface normal of the ribbon at those points), and I'm trying to smoothly interpolate the normal vector over the course of the curve. For example, given a curve which forms the letter 'C', with the first and last control points both having surface normals pointing upwards, the ribbon should start flat, parallel to the ground, slowly turn, and then end flat again, facing the same way as the first control point. To do this "smoothly", it would have to face outwards half-way through the curve. At the moment (for this case), I've only been able to get all the surfaces facing upwards (and not outwards in the middle), which creates an ugly transition in the middle. It's quite hard to explain, I've attached some images below of this example with what it currently looks like (all surfaces facing upwards, sharp flip in the middle) and what it should look like (smooth transition, surfaces slowly rotate round). Silver faces represent the front, black faces the back. Incorrect, what it currently looks like: Correct, what it should look like: All I really need is to be able to calculate this "hybrid normal vector" for any point on the 3D cubic bézier curve, and I can generate the polygons no problem, but I can't work out how to get them to smoothly rotate round as depicted. Completely stuck as to how to proceed!

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Need an advice for unit testing using mock object

- by Andree

Hi there, I just recently read about "Mocking objects" for unit testing and currently I'm having a difficulties implementing this approach in my application. Please let me explain my problem. I have a User model class, which is dependent on 2 data sources (database and facebook web service). The controller class simply use this User model as an interface to access data and it doesn't care about where the data came from. Currently I never done any unit test to this User model because it is dependent on an external web service. But just a while ago, I read about object mocking and now I know that it is a common approach to unit test a class that depends on external resources (like in my case). Now I want to create a unit test for the User model, but then I encountered a design issue: In order for the User model to use a mocked Facebook SDK, I have to inject this mocked Facebook SDK to the User object (probably using a setter). Therefore I can't construct the Facebook SDK inside the User object. I have to construct it outside the User object, and inject the SDK into the User object. The real client of my User model is the application's controller. Therefore I have to construct the Facebook SDK inside the controller and inject it to the user object. Well, this is a problem because I want my controller to be as clean as possible. I want my controller to be ignorant about the application's data source. I'm not good at explaining something systematically, so you'll probably sleeping before reading this last paragraph. But anyway, I want to ask if anyone here ever encountered the same problem as mine? How do you solve this problem? Regards, Andree

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Get settings through a button action

- by Russ Knudsen

I am looking for a way to access user settings (I assume, NSUserDefaults?) through a button action. Let me back up and explain. What I have right now are 2 TextFields a label and a button. The user will type in measurements in the 2 TextFields. When they hit the button the label displays the volume of the measured object in Gallons. That part of it works great. Then I wanted to give the user options to output the volume in Liters instead of gallons. I would also like to give the user options to type in the measurements in Centimeters. So I setup a 'Settings.Bundle' and configured it with 2 'Multi Value' cells (Measurement units and Volumetric Units). Each Multi Value cell has its own list of different units the user can pick from. My main issue is I don't know how to access these settings through the button action. I may be thinking of this wrong, but what I'm looking for is something like; Button Action If settings key = 0 Then do the math in Inches, Display in Gallons If settings key = 1 Then do the math in Centimeters, Display in Gallons If settings key = 2 Then do the math in Inches, Display in Liters If settings key = 3 Then do the math in Centimeters, Display in Liters Etc... Is this possible? Am I thinking of this in the wrong way? What's the best way to do this?

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Managing libraries and imports in a programming language

- by sub

I've created an interpreter for a stupid programming language in C++ and the whole core structure is finished (Tokenizer, Parser, Interpreter including Symbol tables, core functions, etc.). Now I have a problem with creating and managing the function libraries for this interpreter (I'll explain what I mean with that later) So currently my core function handler is horrible: // Simplified version myLangResult SystemFunction( name, argc, argv ) { if ( name == "print" ) { if( argc < 1 ) { Error('blah'); } cout << argv[ 0 ]; } else if ( name == "input" ) { if( argc < 1 ) { Error('blah'); } string res; getline( cin, res ); SetVariable( argv[ 0 ], res ); } else if ( name == "exit ) { exit( 0 ); } And now think of each else if being 10 times more complicated and there being 25 more system functions. Unmaintainable, feels horrible, is horrible. So I thought: How to create some sort of libraries that contain all the functions and if they are imported initialize themselves and add their functions to the symbol table of the running interpreter. However this is the point where I don't really know how to go on. What I wanted to achieve is that there is e.g.: an (extern?) string library for my language, e.g.: string, and it is imported from within a program in that language, example: import string myString = "abcde" print string.at( myString, 2 ) # output: c My problems: How to separate the function libs from the core interpreter and load them? How to get all their functions into a list and add it to the symbol table when needed? What I was thinking to do: At the start of the interpreter, as all libraries are compiled with it, every single function calls something like RegisterFunction( string namespace, myLangResult (*functionPtr) ); which adds itself to a list. When import X is then called from within the language, the list built with RegisterFunction is then added to the symbol table. Disadvantages that spring to mind: All libraries are directly in the interpreter core, size grows and it will definitely slow it down.

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Long running method causing race condition

- by keeleyt83

Hi, I'm relatively new with hibernate so please be gentle. I'm having an issue with a long running method (~2 min long) and changing the value of a status field on an object stored in the DB. The pseudo-code below should help explain my issue. public foo(thing) { if (thing.getStatus() == "ready") { thing.setStatus("finished"); doSomethingAndTakeALongTime(); } else { // Thing already has a status of finished. Send the user back a message. } } The pseudo-code shouldn't take much explanation. I want doSomethingAndTakeALongTime() to run, but only if it has a status of "ready". My issue arises whenever it takes 2 minutes for doSomethingAndTakeALongTime() to finish and the change to thing's status field doesn't get persisted to the database until it leaves foo(). So another user can put in a request during those 2 minutes and the if statement will evaluate to true. I've already tried updating the field and flushing the session manually, but it didn't seem to work. I'm not sure what to do from here and would appreciate any help. PS: My hibernate session is managed by spring.

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Setting CPU target to x86 on .NET 2.0 project adds .NET 3.5 dependencies.

- by AngryHacker

I have a project in VS2008 that targets .NET 2.0 framework. It was original set to build for AnyCPU. I changed it to x86 and for whatever reason, VS adds the following lines to .csproj: <ItemGroup> <BootstrapperPackage Include="Microsoft.Net.Client.3.5"> <Visible>False</Visible> <ProductName>.NET Framework Client Profile</ProductName> <Install>false</Install> </BootstrapperPackage> ... ... <BootstrapperPackage Include="Microsoft.Net.Framework.3.5.SP1"> <Visible>False</Visible> <ProductName>.NET Framework 3.5 SP1</ProductName> <Install>false</Install> </BootstrapperPackage> </ItemGroup> Can someone explain as to why this is being added and whether I can safely remove it, as I still have to target the .NET 2.0 framework. Thanks.

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Java/Hibernate using interfaces over the entities.

- by Dennetik

I am using annoted Hibernate, and I'm wondering whether the following is possible. I have to set up a series of interfaces representing the objects that can be persisted, and an interface for the main database class containing several operations for persisting these objects (... an API for the database). Below that, I have to implement these interfaces, and persist them with Hibernate. So I'll have, for example: public interface Data { public String getSomeString(); public void setSomeString(String someString); } @Entity public class HbnData implements Data, Serializable { @Column(name = "some_string") private String someString; public String getSomeString() { return this.someString; } public void setSomeString(String someString) { this.someString = someString; } } Now, this works fine, sort of. The trouble comes when I want nested entities. The interface of what I'd want is easy enough: public interface HasData { public Data getSomeData(); public void setSomeData(Data someData); } But when I implement the class, I can follow the interface, as below, and get an error from Hibernate saying it doesn't know the class "Data". @Entity public class HbnHasData implements HasData, Serializable { @OneToOne(cascade = CascadeType.ALL) private Data someData; public Data getSomeData() { return this.someData; } public void setSomeData(Data someData) { this.someData = someData; } } The simple change would be to change the type from "Data" to "HbnData", but that would obviously break the interface implementation, and thus make the abstraction impossible. Can anyone explain to me how to implement this in a way that it will work with Hibernate?

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JasperReports reports access image via authenticated URL

- by user363115

Hi all, I am hoping that this is a simple issue with a simple solution and that I have missed something obvious. Let me explain the problem; We have an application that generates PDF reports (using Jasper). These reports contain data from our database, as well as imagery (photographs). These photographs are stored in S3. We use signed URLs to access these photographs. We link these photographs into our Jasper reports using these S3 URLs. Because the S3 URLs are signed and time-limited (by design), the process is as follows; User requests a report to be generated, Report is filled, and goes to our database (at which time UUIDs to any required images are retrieved), For each UUID an S3 signed URL must be generated, To do this the URL behind each report image is a call to an authenticated URL in our app (/get_img?uuid=foo), The controller behind this URL generates a signed S3 URL and returns it, Reports loads the image. The problem is with step (4) - the call to the authenticated URL fails because Jasper does not pass any authentication information with the request. Is there a solution here? Thanks all for your time. Ben

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C# Interface Method calls from a controller

- by ArjaaAine

I was just working on some application architecture and this may sound like a stupid question but please explain to me how the following works: Interface: public interface IMatterDAL { IEnumerable<Matter> GetMattersByCode(string input); IEnumerable<Matter> GetMattersBySearch(string input); } Class: public class MatterDAL : IMatterDAL { private readonly Database _db; public MatterDAL(Database db) { _db = db; LoadAll(); //Private Method } public virtual IEnumerable<Matter> GetMattersBySearch(string input) { //CODE return result; } public virtual IEnumerable<Matter> GetMattersByCode(string input) { //CODE return results; } Controller: public class MatterController : ApiController { private readonly IMatterDAL _publishedData; public MatterController(IMatterDAL publishedData) { _publishedData = publishedData; } [ValidateInput(false)] public JsonResult SearchByCode(string id) { var searchText = id; //better name for this var results = _publishedData.GetMattersBySearch(searchText).Select( matter => new { MatterCode = matter.Code, MatterName = matter.Name, matter.ClientCode, matter.ClientName }); return Json(results); } This works, when I call my controller method from jquery and step into it, the call to the _publishedData method, goes into the class MatterDAL. I want to know how does my controller know to go to the MatterDAL implementation of the Interface IMatterDAL. What if I have another class called MatterDAL2 which is based on the interface. How will my controller know then to call the right method? I am sorry if this is a stupid question, this is baffling me.

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Static and Dynamic Scooping Problem

- by Devyn

Hi, I'm solving following code in Static and Dynamic Scooping. I got following answer but I need someone to confirm if I'm correct or not since I'm a bit confusing. I really appreciate if anyone can explain in simple way! Static => (1)8 (2)27 Dynamic => (1)10 (2)27 proc main var x,y,z; proc sub1 var x,z x := 6; z := 7; sub2; x := y*z + x; print(x); ---- (2) end; proc sub2 var x,y x := 1; y := x+z+2; print(y); ---- (1) end; begin x := 1; y:=3; z:=5; sub1; end

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Random forests for short texts

- by Jasie

Hi all, I've been reading about Random Forests (1,2) because I think it'd be really cool to be able to classify a set of 1,000 sentences into pre-defined categories. I'm wondering if someone can explain to me the algorithm better, I think the papers are a bit dense. Here's the gist from 1: Overview We assume that the user knows about the construction of single classification trees. Random Forests grows many classification trees. To classify a new object from an input vector, put the input vector down each of the trees in the forest. Each tree gives a classification, and we say the tree "votes" for that class. The forest chooses the classification having the most votes (over all the trees in the forest). Each tree is grown as follows: If the number of cases in the training set is N, sample N cases at random - but with replacement, from the original data. This sample will be the training set for growing the tree. If there are M input variables, a number m « M is specified such that at each node, m variables are selected at random out of the M and the best split on these m is used to split the node. The value of m is held constant during the forest growing. Each tree is grown to the largest extent possible. There is no pruning. So, does this look right? I'd have N = 1,000 training cases (sentences), M = 100 variables (let's say, there are only 100 unique words across all sentences), so the input vector is a bit vector of length 100 corresponding to each word. I randomly sample N = 1000 cases at random (with replacement) to build trees from. I pick some small number of input variables m « M, let's say 10, to build a tree off of. Do I build tree nodes randomly, using all m input variables? How many classification trees do I build? Thanks for the help!

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Developping an online music store

- by Simon

We need to develop an application to sell music online. No need to specify that all will be done quite legally and in so doing, we have to plan an interface to pay artists. However, we are confronted with a question: What is the best way to store music on the server? Should we save it on server's disk from a HTTP fileupload? Should we save via FTP or would it be wiser to save it in the database? No need to say that we need it to be the most safiest as possible. So maybe an https is required here. But, we what you think is the best way? Maybe other idea? Because in all HTTP case, upload songs (for administration) is quite long and boring, but easly linkable to a song that admin create in his web application comparativly to an FTP application to upload song on server and then list directory in admin part to link the correct uploaded song to the song informations in database. I know that its maybe not quite clear, it's because i'm french but tell me and I will try to explain part that you don't understand.

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PHP preg_match: a pattern which satisfies all MySQL field names (including 'table.field' formations)

- by gsquare567

i need a pattern which satisfies mysql field names, but also with the option of having a table name before it examples: mytable.myfield myfield my4732894__7289FiEld here's what i tried: $pattern = "/^[a-zA-Z0-9_]*?[\.[a-zA-Z0-9_]]?$/"; this worked for what i needed before, which was just the field name: $pattern = "/^[a-zA-Z0-9_]*$/"; any ideas why my addition isnt working? maybe i'm making up regex, so i'll explain what i added... the first '?' is to say that it isn't greedy, ie. it will stop if the next part, namely "[.[a-zA-Z0-9_]]?" is satisfied. now, that second part is just the same as the first except it is optional (hence the '?' at the end) and it starts with a period (hence the '[.' and ']' wrapping my old clause. and obviously, the "^" and "$" rep the beginning and end of the string so... any ideas? (also, i'm a tad confused as to why i need to put in those "/"s in the begining/end anyways, so if you could tell me why it's required, that'd be awesome) thanks a lot! (and thanks for reading this all if you actually did... it's quite a ramble)

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how does MySQL implement the "group by"?

- by user188916

I read from the MySQL Reference Manual and find that when it can take use of index,it just do index scan,other it will create tmp tables and do things like filesort. And I also read from other article that the "Group By" result will sort by group by columns by default,if "order by null" clause added,it won't don filesort. The difference can be found from the "explain ..." clause. so my problem is:what is the difference between "group by" clause that with "order by null" and which doesn't have? I try to use profiling to see what mysql do on the background,and only see result like: result for group clause without order by null: |preparing | 0.000016 | | Creating tmp table | 0.000048 | | executing | 0.000009 | | Copying to tmp table | 0.000109 | **| Sorting result | 0.000023 |** | Sending data | 0.000027 | result for clause with "order by null": preparing | 0.000016 | | Creating tmp table | 0.000052 | | executing | 0.000009 | | Copying to tmp table | 0.000114 | | Sending data | 0.000028 | So I guess what MySQL do when the "order by null" added,it does not use filesort algorithm,maybe when it creates the tmp table,it uses index as well,and then use the index to do group by operation,when completed,it just read result from the table rows and does not sort the result. But my original opinion is that MySQL can use quicksort to sort the items and then do group by,so the result will be sorted as well. Any opinion appreciated,thanks.

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Can I use foreign key restrictions to return meaningful UI errors with PHP

- by Shane

I want to start by saying that I am a big fan of using foreign keys and have a tendency to use them even on small projects to keep my database from being filled with orphaned data. On larger projects I end up with gobs of keys which end up covering upwards of 8 - 10 layers of data. I want to know if anyone could suggest a graceful way of handling 'expected errors' from the MySQL database in a way that I can construct meaningful messages for the end user. I will explain 'expected errors' with an example. Lets say I have a set of tables used for basic discussions: discussion questions responses users Hierarchically they would probably look something like this: -users --discussion ---questions ----responses When I attempt to delete a user the FKs will check discussions and if any discussion exist the deletion is restricted, deleting discussion checks questions, deleting questions checks responses. An 'expected error' in this case would be attempting to delete a user--unless they are newly created I can anticipate that one or more foreign keys will fail causing an error. What I WANT to do is to catch that error on deletion and be able to tell the end user something like 'We're sorry, but all discussions must be removed before you can delete this user...'. Now I know I can keep and maintain matching arrays in PHP and map specific errors to messages but that is messy and prone to becoming stagnant, or I could manually run a set of selects prior to attempting the deletion, but then I am doing just as much work as without using FKs. Any help here would be greatly appreciated, or if I am just looking at this completely wrong then please let me know. On a side note I generally use CodeIgniter for my application development, so if that would open up an avenue through that framework please consider that in your answers. Thanks in Advance

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problem with two key ranges in couchdb

- by Duasto

I'm having problem getting the right results in my coordinate system. To explain my system, I have this simple database that have x_axis, y_axis and name columns. I don't need to get all the data, I just need to display some part of it. For example, I have a coordinate system that have 10:10(meaning from x_axis -10 to 10 and from y_axis -10 to 10) and I want to display only 49 coordinates. In sql query I can do it something like this: "select * from coordinate where x_axis = -3 and x_axis <= 3 and y_axis = -3 y_axis <= 3" I tried this function but no success: "by_range": { "map": "function(doc) { emit([doc.x_axis, doc.y_axis], doc) }" } by_range?startkey=[-3,-3]&endkey=[3,3] I got a wrong results of: -3x-3 -3x-2 -3x-1 -3x0 -3x1 -3x2 -3x3 <-- should not display this part -- -3x4 -3x5 -3x6 -3x7 -3x8 -3x9 -3x10 <-- end of should not display this part -- ..... up to 3x3 to give you a better understanding of my project here is the screenshot of that I want to be made: Oops they don't allowed new poster to post an image img96(dot)imageshack(dot)us/img96/5382/coordinates(dot)jpg <<< just change the "(dot)" to "."

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