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• Linq-to-sql join/where?

  - by Curtis White

  I've the following table structures Users id Types id isBool UsersTypes userid types I want to select all the UserTypes based on id and isBool. I tried this query var q = from usertype in usertypes from type in types where type.isBool == false where userstypes.user == id select usertype; But this did not work as expected. My questions are: Why? Is there any difference in using the join on syntax vs where, where vs where cond1 && cond2? My understanding is query optimizer will optimize. Is there any difference in using where cond1 == var1 && cond2 == var2 with and without the parenthesis? This seems peculiar that it is possible to build this without parenthesis What type of query do I need in this case? I can see that I could do a subquery or use a group but not 100% sure if it is required. An example might be helpful. I'm thinking a subquery may be required in this case.

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• How to access parents' members from a inner class in WPF?

  - by black sensei

  Hello Experts! I'm trying to do scheduled operation let's say to check for user's credit left via web service call and update the user interface. i've tried with quartz.net to implement the scheduling bit.i created an inner class in the window class i need to update.That inner class has the method that calls the webservice and the result needs to be displayed back to the UI. here is an example of what i did. public partial class Window2 : Window { private int i; public Window2() { InitializeComponent(); } public class Myclass :IJob { public void Execute(JobExecutionContext context) { string result = doMyOperation(); //i'll like to call parent label member of name lblNotif //is something like parent.lblNotif.Content = result; //possible? } public string doMyOperation() { //calling the wermethod to retreive user's balance return result = service.GetUsersBalace(user); } } } Well the quartz bit is working and this post is not about quartz. here are my questions Question 1 : How is it possible to access Window2 controls, for instace lable lblNotif? Question 2 : If my thinking about this is wrong, what is done as best practice to solve my kind of problem, where an application need to do an operation let's say every 5mn and update the the UI. Question 3 : i at first tried to use the backgroundworker and i felt like i can't do the scheduling bit with it.Is that correct or i'm wrong. thanks for those who commented already and sorry for those who didn't get the meaning of my post.I hope this will be a bit clearer.Thanks for reading

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• create CLLocationCoordinate2D from array

  - by shani

  I have a plist with dictionary of array's with coordinates (stored as strings). I want to create a CLLocationCoordinate2D from every array and crate an overlay for the map. I did that - NSString *thePath = [[NSBundle mainBundle] pathForResource:@"Roots" ofType:@"plist"]; NSDictionary *pointsDic = [[NSDictionary alloc] initWithContentsOfFile:thePath]; NSArray *pointsArray = [NSArray arrayWithArray:[pointsDic objectForKey:@"roade1"]]; CLLocationCoordinate2D pointsToUse[256]; for(int i = 0; i < 256; i++) { CGPoint p = CGPointFromString([pointsArray objectAtIndex:i]); pointsToUse[i] = CLLocationCoordinate2DMake(p.x,p.y); NSLog(@"coord %f",pointsToUse [i].longitude); NSLog(@"coord %f",pointsToUse [i].latitude); } MKPolyline *myPolyline = [MKPolyline polylineWithCoordinates:pointsToUse count:256]; [[self mv] addOverlay:myPolyline]; but the app is crashing without any error. (BTW when i remove the addOverLay method the app does not crash). I have 2 questions- What am i doing wrong? I have tried to set the pointsArray count as the argument for the CLLocationCoordinate2D like that - CLLocationCoordinate2D pointsToUse[pointsArray count]; And i am getting an error. How can i set the CLLocationCoordinate2D dynamically ? Thanks for any help. Shani

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• What's the steps for SQL optimization and changes without reflect live system ?

  - by Space Cracker

  we have a big portal that build using SharePoint 2007 , asp.net 3.5 , SQL Server 2005 .. many developers work in it since 01/2008 and we are now doing huge analysis for current SQL Databases [not share-point DB ] to optimize and enhance it. The main db have about 330 table and 1720 stored procedure (SP) created from 01/2008 till now Many table names / Columns is very long and we want to short it we found SP names is written in 25 format :( , some of them are very complex and also we want to rename many SP parameters need to be renamed one of the biggest table is Registered user table, that will be spitted in more than one table for some optimization, many columns name will be changed I searched for the way that i can rename table names ,columns and i found SQL refactor tool but i still trying it .. my questions : Is SQl Refactor is the best tool for renaming ? or is there any other one ? if i want to make it manually, is there any references or best practice for that ? How can i do such changes in fast and stable way .. i search for recommendations and case studies if exist ?

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• C function prototype: void f(). Is it recommended?

  - by ycalleecharan

  Hi, I'm learning C and I saw in a book that a function prototype has the form void f() and in the function declaration or in the calling function, the f function takes arguments. Thus In the function declaration we have something like void f(long double y[], long double A) and in the calling function is f(y, A). The function is doing operations on the array y i.e. when the function is called, some elements in the array y are changing. A is just a constant numerical value that doesn't change. I have two questions: If defining the function prototype at the top in the program as void f() a good practice? Or is it better to put it as void f(long double y[], long double A) as in the function declaration? The called function f is changing elements in the array y. Is void the right return type? The program is working fine as such with the void as described. Or should I change all my "voids" to "long double". I'm working with long double as I need as much precision as possible though on my machine both double and long double gives me 15 precision digits. Thanks a lot

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• Prevent coersion to a single type in unlist() or c(); passing arguments to wrapper functions

  - by Leo Alekseyev

  Is there a simple way to flatten a list while retaining the original types of list constituents?.. Is there a way to programmatically construct a heterogeneous list?.. For instance, I want to create a simple wrapper for functions like png(filename,width,height) that would take device name, file name, and a list of options. The naive approach would be something like my.wrapper <- function(dev,name,opts) { do.call(dev,c(filename=name,opts)) } or similar code with unlist(list(...)). This doesn't work because opts gets coerced to character, and the resulting call is e.g. png(filename,width="500",height="500"). If there's no straightforward way to create heterogeneous lists like that, is there a standard idiomatic way to splice arguments into functions without naming them explicitly (e.g. do.call(dev,list(filename=name,width=opts["width"]))? -- Edit -- Gavin Simpson answered both questions below in his discussion about constructing wrapper functions. Let me give a summary of the answer to the title question: It is possible to construct a heterogeneous list with c() provided the arguments to c() are lists. To wit: > foo <- c("a","b"); bar <- 1:3 > c(foo,bar) [1] "a" "b" "1" "2" "3" > c(list(foo),list(bar)) [[1]] [1] "a" "b" [[2]] [1] 1 2 3 > c(as.list(foo),as.list(bar)) ## this creates a flattened heterogeneous list [[1]] [1] "a" [[2]] [1] "b" [[3]] [1] 1 [[4]] [1] 2 [[5]] [1] 3

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• Thread-Safe lazy instantiating using MEF

  - by Xaqron

  // Member Variable private static readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { // It seems the `IsValueCreated` is not up-to-date if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile static int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. I should notice the CompositionContainer has a thread-safe option in constructor which is already used. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• Looking forward to a programming future but confused where to start.

  - by Kraivyne

  Hi there, I am very new to this site and to programming. I started doing some basic programming with python a few weeks ago and recently, messing around with Java basics. My main problem is that I am completely overwhelmed and haven't got the slightest clue where I should be starting. I want to learn programming because I really enjoy doing it, the simple applications that I have managed to conjure up put a smile on my face. My plan is to eventually (by eventually I'm talking about 6 years+) go into games programming. I have been informed that C++ is the best way to go about this but haven't got the slightest clue what book/sight is optimal for someone who is still learning the very basics. These are my questions: I have been to the Definitive C++ Book Guide but am still unsure which book is best to start of with. Should I stick with Python or Java instead of moving on to C++? Is there any advice you would give to a beginner programmer? Thanks again for all your help.

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• How to strongly type properties in JavaScript that map to models in C# ?

  - by Roberto Sebestyen

  I'm not even sure if I worded the question right, but I'll try and explain as clearly as possible with an example: In the following example scenario: 1) Take a class such as this: public class foo { public string firstName {get;set;} public string lastName {get;set} } 2) Serialize that into JSON, pass it over the wire to the Browser. 3) Browser de-serializes this and turns the JSON into a JavaScript object so that you can then access the properties like this: var foo = deSerialize("*******the JSON from above**************"); alert(foo.firstName); alert(foo.lastName); What if now a new developer comes along working on this project decides that firstName is no longer a suitable property name. Lets say they use ReSharper to rename this property, since ReSharper does a pretty good job at finding (almost) all the references to the property and renaming them appropriately. However ReSharper will not be able to rename the references within the JavaScript code (#3) since it has no way of knowing that these also really mean the same thing. Which means the programmer is left with the responsibility of manually finding these references and renaming those too. The risk is that if this is forgotten, no one will know about this error until someone tests that part of the code, or worse, slip through to the customer. Back to the actual question: I have been trying to think of a solution to this to some how strongly type these property names when used in javascript, so that a tool like ReSharper can successfully rename ALL usages of the property? Here is what I have been thinking for example (This would obviously not work unless i make some kind of static properties) var foo = deSerialize("*******the JSON from above**************"); alert(foo.<%=foo.firstName.GetPropertyName()%>) alert(foo.<%=foo.lastName.GetPropertyName()%>) But that is obviously not practical. Does anyone have any thoughts on this? Thanks, and kudos to all of the talented people answering questions on this site.

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• Why should I prefer OSGi Services over exported packages?

  - by Jens

  Hi, I am trying to get my head around OSGi Services. The main question I keep asking myself is: What's the benefit of using services instead of working with bundles and their exported packages? As far as I know it seems the concept of Late Binding has something to do with it. Bundle dependencies are wired together at bundle start, so they are pretty fixed I guess. But with services it seems to be almost the same. A bundle starts and registers services or binds to services. Of course services can come and go whenever they want and you have to keep track of these chances. But the core idea doesn't seem that different to me. Another aspect to this seems to be that services are more flexible. There could be many implementations for one specific Interface. On the other hand there can be a lot of different implementations for a specific exported package too. In another text I read that the disadvantage of using exported packages is that they make the application more fragile than services. The author wrote that if you remove one bundle from the dependency graph other dependencies would no longer be met, thus possibly causing a domino effect on the whole graph. But couldn't the same happen if a service would go offline? To me it looks like service dependencies are no better than bundle dependencies. So far I could not find a blog post, book or presentation that could clearly describe why services are better than just exposing functionality by exporting and importing packages. To sum my questions up: What are the key benefits of using OSGi Services that make them superior to exporting and importing packages?

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• How do I simplify my code?

  - by Mitchell Skurnik

  I just finished creating my first major application in C#/Silverlight. In the end the total line count came out to over 12,000 lines of code. Considering this was a rewrite of a php/javascript application I created 2 years that was over 28,000 lines I am actually quite proud of my accomplishment. After reading many questions and answers here on stackoverflow and other sites online, I followed many posters advice: I created classes, procedures, and such for things that I would have a year ago copied and pasted; I created logic charts to figure out complex functions; making sure there are no crazy hidden characters (used tabs instead of spaces); and a few others things; place comments where necessary (I have lots of comments). My application consists of 4 tiles laid out horizontally that have user controls loaded into each slice. You can have between one and four slices loaded at anytime. If you have once slice loaded, the slice takes up the entire artboard...if you have 2 loaded, each take up half, 3 a third, 4 a quarter. Each one of these slices represent (for the sake of this example) a light control. Each slice has 3 slider controls in it. Now when I coded the functionality of the sliders, I used a switch/case statement inside of a public function that would run the command on the specified slice/slider. The made for some duplicate code but I saw no way around it as each slice was named differently. So I would do slice1.my.commands(); slice2.my.commands(); etc. My question to you is how do I clean up my code even futher? (Sadly I cannot post any of my code). Is there any way to take this repetion out of my code?

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• Problem understanding Inheritance

  - by dhruvbird

  I've been racking my brains over inheritance for a while now, but am still not completely able to get around it. For example, the other day I was thinking about relating an Infallible Human and a Fallible Human. Let's first define the two: Infallible Human: A human that can never make a mistake. It's do_task() method will never throw an exception Fallible Human: A human that will occasionally make a mistakes. It's do_task() method may occasionally throw a ErrorProcessingRequest Exception The question was: IS an infallible human A fallible human OR IS a fallible human AN infallible human? The very nice answer I received was in the form of a question (I love these since it gives me rules to answer future questions I may have). "Can you pass an infallible human where a fallible human is expected OR can you pass a fallible human where an infallible human is expected?" It seems apparent that you can pass an infallible human where a fallible human is expected, but not the other way around. I guess that answered my question. However, it still feels funny saying "An infallible human is a fallible human". Does anyone else feel queasy when they say it? It almost feels as if speaking out inheritance trees is like reading out statements from propositional calculus in plain English (the if/then implication connectives don't mean the same as that in spoken English). Does anyone else feel the same?

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• Django: getting the list of related records for a list of objects

  - by Silver Light

  Hello! I have two models related one-to many: class Person(models.Model): name = models.CharField(max_length=255); surname = models.CharField(max_length=255); age = models.IntegerField(); class Dog(models.Model): name = models.CharField(max_length=255); owner = models.ForeignKey('Person'); I want to output a list of persons below each person a list of dogs he has. Here's how I can do it: in view: persons = Person.objects.all()[0:100]; in template: {% for p in persons %} {{ p.name }} has dogs:<br /> {% for d in persons.dog_set.all %} - {{ d.name }}<br /> {% endfor %} {% endfor %} But if I do it like that, Django will execute 101 SQL queries which is very inefficient. I tried to make a custom manager, which will get all the persons, then all the dogs and links them in python, but then I can't use paginator (my another question: http://stackoverflow.com/questions/2532475/django-paginator-raw-sql-query ) and it looks quite ugly. Is there a more graceful way doing this?

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• Is this a good way to generically deserialize objects?

  - by Damien Wildfire

  I have a stream onto which serialized objects representing messages are dumped periodically. The objects are one of a very limited number of types, and other than the actual sequence of bytes that arrives, I have no way of knowing what type of message it is. I would like to simply try to deserialize it as an object of a particular type, and if an exception is thrown, try again with the next type. I have an interface that looks like this: public interface IMessageHandler<T> where T : class, IMessage { T Handle(string message); } // elsewhere: // (These are all xsd.exe-generated classes from an XML schema.) public class AppleMessage : IMessage { ... } public class BananaMessage : IMessage { ... } public class CoconutMessage : IMessage { ... } Then I wrote a GenericHandler<T> that looks like this: public class GenericHandler<T> : IMessageHandler<T> where T: class, IMessage { public class MessageHandler : IMessageHandler { T IMessageHandler.Handle(string message) { T result = default(T); try { // This utility method tries to deserialize the object with an // XmlSerializer as if it were an object of type T. result = Utils.SerializationHelper.Deserialize<T>(message); } catch (InvalidCastException e) { result = default(T); } return result; } } } Two questions: Using my GenericHandler<T> (or something similar to it), I'd now like to populate a collection with handlers that each handle a different type. Then I want to invoke each handler's Handle method on a particular message to see if it can be deserialized. If I get a null result, move onto the next handler; otherwise, the message has been deserialized. Can this be done? Is there a better way to deserialize data of unknown (but restricted) type?

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• How do disable Rails submit buttons alongside Prototype helpers & RJS?

  - by Jesse

  I'm trying to follow this post http://stackoverflow.com/questions/576240/how-can-i-unobtrusively-disable-submit-buttons-with-javascript-and-prototype but I can't get it to work. The form triggers an RJS function, so I need to keep the helpers' onclick events intact. The RJS returns/reloads the same forms along with two new texts. I'm really confused. Here is my rails code for the forms: .span-20#comparison / new comparison . . . / voting forms (also reloaded) .span-4.prepend-3.append-6 - form_remote_tag :action => url_for(:controller => :comparisons), :method => :post do = hidden_field_tag :poem1_id, poems[:a].id = hidden_field_tag :poem2_id, poems[:b].id = hidden_field_tag :response, 1 = submit_tag "Vote for me", :disabled => false, :disable_with => 'Vote for me', :class => "compare" .span-4.append-3.last - form_remote_tag :action => url_for(:controller => :comparisons), :method => :post do = hidden_field_tag :poem1_id, poems[:a].id = hidden_field_tag :poem2_id, poems[:b].id = hidden_field_tag :response, 2 = submit_tag "Vote for me", :disable_with => 'Vote for me', :class => "compare" .span-4.prepend-8.append-8.prepend-top.last - form_remote_tag :action => url_for(:controller => :comparisons), :method => :post do = hidden_field_tag :poem1_id, poems[:a].id = hidden_field_tag :poem2_id, poems[:b].id = hidden_field_tag :response, 'draw' = submit_tag "Declare Draw", :disable_with => 'Declare Draw', :class => "compare" RJS page.replace_html :comparison, :partial => 'poems', :object => @poems page.insert_html :top, :previous, :partial => 'comparison', :object => @comparison page << "Effect.ScrollTo($('top'));"

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• Why is function's length information of other shared lib in ELF?

  - by minastaros

  Our project (C++, Linux, gcc, PowerPC) consists of several shared libraries. When releasing a new version of the package, only those libs should change whose source code was actually affected. With "change" I mean absolute binary identity (the checksum over the file is compared. Different checksum - different version according to the policy). (I should mention that the whole project is always built at once, no matter if any code has changed or not per library). Usually this can by achieved by hiding private parts of the included Header files and not changing the public ones. However, there was a case where just a delete was added to the destructor of a class TableManager (in the TableManager.cpp file!) of library libTableManager.so, and yet the binary/checksum of library libB.so (which uses class TableManager ) has changed. TableManager.h: class TableManager { public: TableManager(); ~TableManager(); private: int* myPtr; } TableManager.cpp: TableManager::~TableManager() { doSomeCleanup(); delete myPtr; // this delete has been added } By inspecting libB.so with readelf --all libB.so, looking at the .dynsym section, it turned out that the length of all functions, even the dynamically used ones from other libraries, are stored in libB! It looks like this (length is the 668 in the 3rd column): 527: 00000000 668 FUNC GLOBAL DEFAULT UND _ZN12TableManagerD1Ev So my questions are: Why is the length of a function actually stored in the client lib? Wouldn't a start address be sufficient? Can this be suppressed somehow when compiling/linking of libB.so (kind of "stripping")? We would really like to reduce this degree of dependency...

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• Serialport List Read problem and NullReferenceException?

  - by Plumbum7

  Hello everybody, Using Microsoft VC# 2008 Express (little fact about me : non experience in c#, programskills further very beginnerlevel. This peace op program is to communicate with Zigbee switching walloutlets (switching, status info). and is downloaded from http://plugwiselib.codeplex.com/SourceControl/list/changesets The problem: NullRefferenceException was UnHandled private void port_DataReceived(object sender, SerialDataReceivedEventArgs e) {// Event for receiving data string txt = port.ReadExisting(); Console.WriteLine(txt); List<PlugwiseMessage> msg = reader.Read (Regex.Split (txt, "\r\n" )); //Console.WriteLine( msg ); DataReceived(sender, new System.EventArgs(), msg); VC# Marks the last line and says msg is empty. so i looked further. Msg come's from txt text is filled with "000002D200C133E1\r\nPutFifoUnicast 40 : Handle 722 :"< so it goes wrong in or reader.Read or in the List so i looked further: public List<PlugwiseMessage> Read(string[] serialData) { Console.WriteLine(serialData); List<PlugwiseMessage> output = new List<PlugwiseMessage>(); Console.WriteLine(output); Both (serialData) as (output); are empty. So can i assume that the problem is in: Read(string[] serialData) But now the questions, Is Read(string[] serialData) something which is a Windows.Refence or is is from a Method ? and IF this is so is this then reader.READ (how can i find this)? (answered my own question proberly)(method reader)(private PlugwiseReader reader) So why isn't is working trough the serialData ? or is it the List<PlugwiseMessage> part, but i have no idea how it is filled can sombody help me ?

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• Context path routing in Tomcat ( service swapping )

  - by jojovilco

  Here is what I would like to achieve: I have a web service A which I want to be able to deploy side by side with other web services of type A - different version(s). For now I assume 2 instances side by side. I need it because the service has a warm up stage, which takes some time to build up stuff from DB and only after it is ready it can start serving requests ... I was thinking to deploy to Tomcat context paths like: "/ServiceA-1.0", "/ServiceA-2.0" and then have a "virtual" context like "/ServiceA" which will point to the desired physical service e.g. "/ServiceA-1.0". So external world will know about ServiceA, but internally, my ServiceA related stack would know about versioned ServiceA url ( there are more components involved but only ServiceA is serving outer world ). When new service is ready, I would just reconfigure the "virtual" context to point to a new service. So far, I was not able to find out how to do this with Tomcat and starting to tkink it is not possible. I found suggestions to place Apache Server in front of Tomcat and do the routing there, but I do not want to enroll another piece of software unless necessary. My questions are: - is this kind of a "virtual" context and routing possible to do with Tomcat? - any other options, wisdom and lessons learned how to achieve this kind of service swapping scenario? Best, Jozef

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• Can I use my objects without fully populating them?

  - by LuckySlevin

  I have situation. I have to create a Sports Club system in JAVA. There should be a class your for keeping track of club name, president name and braches the club has. For each sports branch also there should be a class for keeping track of a list of players. Also each player should have a name, number, position and salary. So, I come up with this. Three seperate classes: public class Team { String clubName; String preName; Branch []branches; } public class Branch { Player[] players; } public class Player { String name; String pos; int salary; int number; } The problems are creating Branch[] in another class and same for the Player[]. Is there any simplier thing to do this? For example, I want to add info for only the club name, president name and branches of the club, in this situation, won't i have to enter players,names,salaries etc. since they are nested in each other. I hope i could be clear. For further questions you can ask.

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• Launching and Intent from file and mime type

  - by stonedonkey

  I've reviewed all the similar questions here, but I can't for the life of me figure out what I'm doing wrong. I've written an application that tries to launch various files, sort of a file browser, when a file is clicked it tries to launch the program based on it's associated MIME type or I want it to present the "Choose Application to Launch" dialog. Here's the code I'm using to launch: File file = new File(app.mediaPath() + "/" +_mediaFiles.get(position)); Intent myIntent = new Intent(android.content.Intent.ACTION_VIEW); String extension = android.webkit.MimeTypeMap.getFileExtensionFromUrl(Uri.fromFile(file).toString()); String mimetype = android.webkit.MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension); myIntent.setDataAndType(Uri.fromFile(file),mimetype); startActivity(myIntent); This fails and generates a: android.content.ActivityNotFoundException: No Activity found to handle Intent { act=android.intent.action.VIEW dat=file:///file:/mnt/sdcard/roms/nes/Baseball_simulator.nes } Now if I install OI File Manager for instance, it opens instead of this error being thrown, and then if I click the same file from within in it, it launches the approriate dialogs. I have noticed that the MIME type for that particular file fails, but other mime types like .zip do return values. Am I missing something that when the MIME type is null to call a dialog that lets the user select? I've tried other variations of launching the app, including not setting the mime type and only using .setData with no success. The action I want to happen is, a user clicks a file, if it's associated with an application that app launches, if not, the user gets the "Complete action using" dialog with a list of apps. Thanks for any advice.

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• Oracle Query Optimization: Why is My Second Query Faster?

  - by Patrick Cuff

  I was having some performance issues with an Oracle query, so I downloaded a trial of the Quest SQL Optimizer for Oracle, which made some changes that dramatically improved the query's performance. I'm not exactly sure why the recommended query had such an improvement; can anyone provide an explanation? Before: SELECT t1.version_id, t1.id, t2.field1, t3.person_id, t2.id FROM table1 t1, table2 t2, table3 t3 WHERE t1.id = t2.id AND t1.version_id = t2.version_id AND t2.id = 123 AND t1.version_id = t3.version_id AND t1.VERSION_NAME <> 'AA' order by t1.id Plan Cost: 831 Elapsed Time: 00:00:21.40 Number of Records: 40,717 After: SELECT /*+ USE_NL_WITH_INDEX(t1) */ t1.version_id, t1.id, t2.field1, t3.person_id, t2.id FROM table2 t2, table3 t3, table1 t1 WHERE t1.id = t2.id + 0 AND t1.version_id = t2.version_id + 0 AND t2.id = 123 AND t1.version_id = t3.version_id + 0 AND t1.VERSION_NAME || '' <> 'AA' AND t3.version_id = t2.version_id + 0 order by t1.id Plan Cost: 686 Elapsed Time: 00:00:00.95 Number of Records: 40,717 Questions: Why does re-arranging the order of the tables in the FROM clause help? Why does adding + 0 to the WHERE clause comparisons help? Why does || '' <> 'AA' in the WHERE clause VERSION_NAME comparison help? Is this a more efficient way of handling possible nulls on this column?

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• Why extremely occasionally will one of bof/eof be true for a new non-empty recordset

  - by jjb

  set recordsetname = databasename.openrecordset(SQLString) if recordsetname.bof <> true and recordsetname.eof <> true then 'do something end if 2 questions : the above test can evaluate to false incorrectly but only extremely rarely (I've had one lurking in my code and it failed today, I believe for the first time in 5 years of daily use-that's how I found it). Why very occasionally will one of bof/eof be true for a non-empty recordset. It seems so rare that I wonder why it occurs at all. Is this a foolproof replacement: if recordsetname.bof <> true or recordsetname.eof <> true then Edit to add details of code : Customers have orders, each order begins with a BeginOrder item and end with an EndOrder item and in between are the items in the order. The SQL is: ' ids are autoincrement long integers ' SQLString = "select * from Orders where type = OrderBegin or type = OrderEnd" Dim OrderOpen as Boolean OrderOpen = False Set rs = db.Openrecordset(SQLString) If rs.bof <> True And rs.eof <> True Then myrec.movelast If rs.fields("type").value = BeginOrder Then OrderOpen = True End If End If If OrderOpen F False Then 'code here to add new BeginOrder Item to Orders table ' End If ShowOrderHistory 'displays the customer's Order history ' In this case which looks this this BeginOrder Item a Item b ... Item n EndOrder BeginOrder Item a Item b ... Item n EndOrder BeginOrder Item a item b ... Item m BeginOrder <----should not be there as previous order still open

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• Which DVCS would work best on Windows for my scenario?

  - by PoorLuzer

  At work I use ClearCase and SourceSafe, but have found some time to do some time to code for myself enroute thanks to a disposable laptop. However, I wish I had a lightweight VCS on my system using which I would be able to make changes to my code during the commute and then push/grab them from my Linux systems. I use git on my home system, but I can't really get it working on Windows. I don't want all that cygwin hack. If it does not run natively on Windows, it just won't do. What have you guys tried on your Windows system? Something that YOU use. The big player at the moment seems to be Mercurial? What would be best for a one (or maybe two) man team? I just need to maintain : Versioned copies of source code. Checking in and out should be as less obtrusive as possible. I am looking forward to a multiple Undo kind of feature (like that in an EMacs buffer) but persistent. I really like the way git keeps track of lines moving between files in a source code set I should be able to move part(s)/sub tree(s) of the source tree (each sub tree implies a module/plugin to my the main software I am building) to an archival system either completly or partially and restore them back from the archive as and when required and the system should track any changes to this tree as well. I actually want to experiment with my code as much as possible without me manually keeping track of what I modified and what I need to undo once I try out some idea, so that I am back to where I want to continue from. Notes : A similar topic came up a year ago : http://stackoverflow.com/questions/4670/dvcs-choices-whats-good-for-windows I hope things have changed, and I really want people to share their own, real life experiences. Not something they recommend without using it or they think will work.

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• C++ traits question

  - by duli

  I have a templated class template <typename Data> class C { ..... } In most situations, I depend on the compiler to let me substitute types for Data. I call methods foo(), goo() on objects of type Data, so what I substitute needs to provide that. I now need to substitute int and string for my Data type. I do not want to specialize because the class is already too big and would require specializing each method (with only small code change). My options (please tell me if there are more) 1) I can provide wrapper classes around int and string which implement the methods foo(), goo() etc 2) provide a traits class traits that calls foo() or goo() on objects of classes that provide foo(),goo() (these are my present substitutable classes) and specialize these classes for int and string. Questions 1) what are the relative merits of 1 vs 2? 2) My traits classes will have static methods. Can a traits class have non-static methods as well? I see most traits classes define constants in the STL. 3) Do I make the traits classes global or should I pass them in as a template parameter for class C?

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• MySQL Join/Comparison on a DATETIME column (<5.6.4 and > 5.6.4)

  - by Simon

  Suppose i have two tables like so: Events ID (PK int autoInc), Time (datetime), Caption (varchar) Position ID (PK int autoinc), Time (datetime), Easting (float), Northing (float) Is it safe to, for example, list all the events and their position if I am using the Time field as my joining criteria? I.e.: SELECT E.*,P.* FROM Events E JOIN Position P ON E.Time = P.Time OR, even just simply comparing a datetime value (taking into consideration that the parameterized value may contain the fractional seconds part - which MySQL has always accepted) e.g. SELECT E.* FROM Events E WHERE E.Time = @Time I understand MySQL (before version 5.6.4) only stores datetime fields WITHOUT milliseconds. So I would assume this query would function OK. However as of version 5.6.4, I have read MySQL can now store milliseconds with the datetime field. Assuming datetime values are inserted using functions such as NOW(), the milliseconds are truncated (<5.6.4) which I would assume allow the above query to work. However, with version 5.6.4 and later, this could potentially NOT work. I am, and only ever will be interested in second accuracy. If anyone could answer the following questions would be greatly appreciated: In General, how does MySQL compare datetime fields against one another (consider the above query). Is the above query fine, and does it make use of indexes on the time fields? (MySQL < 5.6.4) Is there any way to exclude milliseconds? I.e. when inserting and in conditional joins/selects etc? (MySQL 5.6.4) Will the join query above work? (MySQL 5.6.4) EDIT I know i can cast the datetimes, thanks for those that answered, but i'm trying to tackle the root of the problem here (the fact that the storage type/definition has been changed) and i DO NOT want to use functions in my queries. This negates all my work of optimizing queries applying indexes etc, not to mention having to rewrite all my queries. EDIT2 Can anyone out there suggest a reason NOT to join on a DATETIME field using second accuracy?

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