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• Are there good reasons not to use an ORM?

  - by hangy

  During my apprenticeship, I have used NHibernate for some smaller projects which I mostly coded and designed on my own. Now, before starting some bigger project, the discussion arose how to design data access and whether or not to use an ORM layer. As I am still in my apprenticeship and still consider myself a beginner in enterprise programming, I did not really try to push in my opinion, which is that using an object relational mapper to the database can ease development quite a lot. The other coders in the development team are much more experienced than me, so I think I will just do what they say. :-) However, I do not completely understand two of the main reasons for not using NHibernate or a similar project: One can just build one’s own data access objects with SQL queries and copy those queries out of Microsoft SQL Server Management Studio. Debugging an ORM can be hard. So, of course I could just build my data access layer with a lot of SELECTs etc, but here I miss the advantage of automatic joins, lazy-loading proxy classes and a lower maintenance effort if a table gets a new column or a column gets renamed. (Updating numerous SELECT, INSERT and UPDATE queries vs. updating the mapping config and possibly refactoring the business classes and DTOs.) Also, using NHibernate you can run into unforeseen problems if you do not know the framework very well. That could be, for example, trusting the Table.hbm.xml where you set a string’s length to be automatically validated. However, I can also imagine similar bugs in a “simple” SqlConnection query based data access layer. Finally, are those arguments mentioned above really a good reason not to utilise an ORM for a non-trivial database based enterprise application? Are there probably other arguments they/I might have missed? (I should probably add that I think this is like the first “big” .NET/C# based application which will require teamwork. Good practices, which are seen as pretty normal on Stack Overflow, such as unit testing or continuous integration, are non-existing here up to now.)

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• Concise description of how .h and .m files interact in objective c?

  - by RJ86

  I have just started learning objective C and am really confused how the .h and .m files interact with each other. This simple program has 3 files: Fraction.h #import <Foundation/NSObject.h> @interface Fraction : NSObject { int numerator; int denominator; } - (void) print; - (void) setNumerator: (int) n; - (void) setDenominator: (int) d; - (int) numerator; - (int) denominator; @end Fraction.m #import "Fraction.h" #import <stdio.h> @implementation Fraction -(void) print { printf( "%i/%i", numerator, denominator ); } -(void) setNumerator: (int) n { numerator = n; } -(void) setDenominator: (int) d { denominator = d; } -(int) denominator { return denominator; } -(int) numerator { return numerator; } @end Main.m #import <stdio.h> #import "Fraction.h" int main(int argc, char *argv[]) { Fraction *frac = [[Fraction alloc] init]; [frac setNumerator: 1]; [frac setDenominator: 3]; printf( "The fraction is: " ); [frac print]; printf( "\n" ); [frac release]; return 0; } From what I understand, the program initially starts running the main.m file. I understand the basic C concepts but this whole "class" and "instance" stuff is really confusing. In the Fraction.h file the @interface is defining numerator and denominator as an integer, but what else is it doing below with the (void)? and what is the purpose of re-defining below? I am also quite confused as to what is happening with the (void) and (int) portions of the Fraction.m and how all of this is brought together in the main.m file. I guess what I am trying to say is that this seems like a fairly easy program to learn how the different portions work with each other - could anyone explain in non-tech jargon?

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• What's best choice career-wise, to know a little about a lot or a lot about a little?

  - by nimo

  I work as a developer at a rather small company and we are providing a web application that is used by a big base of customers. Because we are so small everyone have to be able to do a lot of different tasks. It ranges from advanced support, developing the product (programming: c/c++, c#, php, sql, javascript, html, css), handle network configuration and network related issues and even sometimes go on sales meetings with potential customers. My concern is that I don't really specialize in any specific area. I know and learn little about a lot. I have graduated from school two years ago and this is my first real employment and when I look at other positions out there they always require so and so many years of experience in a specific area (for example 5 years of C#). For me to get that kind of specialized experience will be really hard at my current job. My question for you is what is, in your opinion, best choice career-wise, to know a little about a lot or a lot about a little? What path did you take? pros and cons that comes with that choice.

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• Android Layout + Programming

  - by MD

  I'm trying to create a "scrollable" layout in Android. Even using developers.android.com, though, I feel a little bit lost at the moment. I'm somewhat new to Java, but not so much that I feel I should be having these issues--being new to Android is the bigger problem right now. The layout I'm trying to create should scroll in a sort of a "grid". I THINK what I'm looking for is the Gallery view, but I'm really lost as to how to implement it at the moment. I want it to "snap" to center the frame, like in the actual Gallery application. Essentially, if I had a photo gallery of 9 pictures, the idea is to scroll between them up/down AND side to side, in a 3x3 manner. Doesn't need to dynamically adjust, or anything like that, I just want a grid I can scroll through. I'm also not asking for anyone to give me explicit code for it--I'm trying to learn, more than anything. But pointing me in the right direction for helpful layout programming resources would be greatly appreciated, and confirming if it's a Gallery view I'm looking for would also be really helpful. Thanks in advance.

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• What's the correct place to share application logic in CakePHP?

  - by Pichan

  I guess simple answer to the question would be a component. Although I agree, I feel weird having to write a component for something so specific. For example, let's say I have a table of users. When a user is created, it should form a chain reaction of events, initiating different kinds of data related to the user all around the database. I figured it would be best to avoid directly manipulating the database from different controllers and instead pack all that neatly in a method. However since some logic needs to be accesed separately, I really can't have the whole package in a single method. Instead I thought it would be logical to break it up to smaller pieces(like $userModelOrController->createNew() and $candyStorageModelOrController->createNew()) that only interact with their respective database table. Now, if the logic is put to the model, it works great until I need to use other models. Of course it's possible, but when compared to loading models in a controller, it's not that simple. It's like a Cake developer telling me "Sure, it's possible if you want to do it that way but that's not how I would do it". Then, if the logic is put to the controller, I can access other models really easy through $this->loadModel(), but that brings me back to the previously explained situation since I need to be able to continue the chain reaction indefinitely. Accessing other controllers from a controller is possible, but again there doesn't seem to be any direct way of doing so, so I'm guessing I'm still not doing it right. By using a component this problem could be solved easily, since components are available to every controller I want. But like I wrote at the beginning, it feels awkward to create a component specifically for this one task. To me, components seem more like packages of extra functionality(like the core components) and not something to share controller-specific logic. Since I'm new to this whole MVC thing, I could've completely misunderstood the concept. Once again, I would be thankful if someone pointed me to the right direction :)

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• using spring, hibernate and scala, is there a better way to load test data than dbunit?

  - by egervari

  Here are some things I really dislike about dbunit: 1) You cannot specify the exact ordering the inserts because dbunit likes to group your inserts by table name, and not by the order you define them in the XML file. This is a problem when you have records depending on other records in other tables, so you have to disable foreign key constraints during your tests... which actually sucks because these foreign key constraints will get fired in production while your tests won't be aware of them! 2) They seem hellbent on forcing you to use an xml namespace to define your xml... and I honestly can't be bothered to do this. I like the data.xml without any namespace. It works. But they are so hellbent on deprecating it. 3) Creating different xml files is hard on a per test basis, so it actually encourages creating data for your entire app. Unfortunately, this process is a little bloated too once the data grows in size and things get inter tangled. There has got to be a better way to split up your test data into chunks without having to copy/paste a lot of the test data across all of your tests. 4) Keeping track of id references in a big xml file is just impossible. If you have 130 domain classes, it just gets bewildering. This model simply does not scale. Is there something less bloated and better in the Spring/Hibernate space? db unit has worn out its welcome and I'm really looking for something better.

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• What's the meaning of the angle brackets on LINQ methods in Intellisense? (Contains<>, Count<>, Dis

  - by user312758

  They usually involve generics. But some methods with generics don't have them, and not all extension methods have them. They've just "been there" since day one, we've all seen them; but I realized I still don't know what they mean, and I can't find the answer anywhere. Now it's really bugging me. Google just turns up results that are about XML, etc. Is this officially documented anywhere? Thanks. EDIT: Well that's just great. Since I just created an account to make my first Stack Overflow post, to get an answer for this burning question; I'm not allowed to post my pretty Intellisense picture, or create a new tag "angle-brackets". I love Stack Overflow, but... what a welcome! Maybe my problem is that they aren't actually called "angle brackets"... ?? Anyway, I guess if you really want to see my beautiful screenshot you could manually go to: http://www.freeimagehosting.net/uploads/6a6c2f3268.png Bump me up please so I can include it in the post, thanks. ;)

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• ListView causing OutOfMemory Error

  - by Michael

  So I am not really given a reason to the right of this error message. I am not exactly sure why this is happening but my guess though is that it has to do with the fact that there are around ~50 good quality drawables. Upon scrolling really fast, the app crashes. I feel as if I am mitigating most common issues with ListView and crashing such as using View Holders as well as only initiating the inflater once. Process: com.example.michael.myandroidappactivity, PID: 20103 java.lang.OutOfMemoryError at android.graphics.BitmapFactory.nativeDecodeAsset(Native Method) Here is the code public class ImageAdapter extends BaseAdapter { private Context context; private ArrayList<Integer> imageIds; private static LayoutInflater inflater; public ImageAdapter(Context _context, ArrayList<Integer> _imageIds) { context = _context; imageIds = _imageIds; } @Override public int getCount() { return imageIds.size(); } @Override public Object getItem(int position) { return null; } @Override public long getItemId(int position) { return 0; } static class ViewHolder{ ImageView img; } @Override public View getView(int position, View convertView, ViewGroup parent) { ViewHolder holder = null; View rowView = null; if(rowView==null) { LayoutInflater inflater = (LayoutInflater) context .getSystemService(Context.LAYOUT_INFLATER_SERVICE); rowView = inflater.inflate(R.layout.listview_layout, parent, false); holder = new ViewHolder(); holder.img = (ImageView) rowView.findViewById(R.id.flag); rowView.setTag(holder); } else { holder = (ViewHolder) rowView.getTag(); } holder.img.setImageResource(imageIds.get(position)); return rowView; } }

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• is it possible to write a program which prints its own source code utilizing a "sequence-generating-

  - by guest

  is it possible to write a program which prints its own source code utilizing a "sequence-generating-function"? what i call a sequence-generating-function is simply a function which returns a value out of a specific interval (i.e. printable ascii-charecters (32-126)). the point now is, that this generated sequence should be the programs own source-code. as you see, implementing a function which returns an arbitrary sequence is really trivial, but since the returned sequence must contain the implementation of the function itself it is a highly non-trivial task. this is how such a program (and its corresponding output) could look like #include <stdio.h> int fun(int x) { ins1; ins2; ins3; . . . return y; } int main(void) { int i; for ( i=0; i<size of the program; i++ ) { printf("%c", fun(i)); } return 0; } i personally think it is not possible, but since i don't know very much about the underlying matter i posted my thoughts here. i'm really looking forward to hear some opinions!

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• Best Functional Approach

  - by dbyrne

  I have some mutable scala code that I am trying to rewrite in a more functional style. It is a fairly intricate piece of code, so I am trying to refactor it in pieces. My first thought was this: def iterate(count:Int,d:MyComplexType) = { //Generate next value n //Process n causing some side effects return iterate(count - 1, n) } This didn't seem functional at all to me, since I still have side effects mixed throughout my code. My second thought was this: def generateStream(d:MyComplexType):Stream[MyComplexType] = { //Generate next value n return Stream.cons(n, generateStream(n)) } for (n <- generateStream(initialValue).take(2000000)) { //process n causing some side effects } This seemed like a better solution to me, because at least I've isolated my functional value-generation code from the mutable value-processing code. However, this is much less memory efficient because I am generating a large list that I don't really need to store. This leaves me with 3 choices: Write a tail-recursive function, bite the bullet and refactor the value-processing code Use a lazy list. This is not a memory sensitive app (although it is performance sensitive) Come up with a new approach. I guess what I really want is a lazily evaluated sequence where I can discard the values after I've processed them. Any suggestions?

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• Exit and rollback everything in script on error

  - by Jan W.

  Hey guys ! I'm in a bit of a pickle here. I have a TSQL script that does a lot of database structure adjustments but it's not really safe to just let it go through when something fails. to make things clear: using MS SQL 2005 it's NOT a stored procedure, just a script file (.sql) what I have is something in the following order BEGIN TRANSACTION ALTER Stuff GO CREATE New Stuff GO DROP Old Stuff GO IF @@ERROR != 0 BEGIN PRINT 'Errors Found ... Rolling back' ROLLBACK TRANSACTION RETURN END ELSE PRINT 'No Errors ... Committing changes' COMMIT TRANSACTION just to illustrate what I'm working with ... can't go into specifics now, the problem ... When I introduce an error (to test if things get rolled back), I get a statement that the ROLLBACK TRANSACTION could not find a corresponding BEGIN TRANSACTION. This leads me to believe that something when REALLY wrong and the transaction was already killed. what I also noticed is that the script didn't fully quit on error and thus DID try to execute every statement after the error occured. (I noticed this when new tables showed up when I wasn't expecting them because it should have rollbacked) any help in this department is welcome if more speficics are needed, ask! greetz

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• How to use linux csplit to chop up massive XML file?

  - by Fred

  Hi everyone, I have a gigantic (4GB) XML file that I am currently breaking into chunks with linux "split" function (every 25,000 lines - not by bytes). This usually works great (I end up with about 50 files), except some of the data descriptions have line breaks, and so frequently the chunk files do not have the proper closing tags - and my parser chokes halfway through processing. Example file: (note: normally each "listing" xml node is supposed to be on its own line) <?xml version="1.0" encoding="UTF-8"?> <listings> <listing><date>2009-09-22</date><desc>This is a description WITHOUT line breaks and works fine with split</desc><more_tags>stuff</more_tags></listing> <listing><date>2009-09-22</date><desc>This is a really annoying description field WITH line breaks that screw the split function</desc><more_tags>stuff</more_tags></listing> </listings> Then sometimes my split ends up like <?xml version="1.0" encoding="UTF-8"?> <listings> <listing><date>2009-09-22</date><desc>This is a description WITHOUT line breaks and works fine with split</desc><more_tags>stuff</more_tags></listing> <listing><date>2009-09-22</date><desc>This is a really annoying description field WITH line breaks ... EOF So - I have been reading about "csplit" and it sounds like it might work to solve this issue. I cant seem to get the regular expression right... Basically I want the same output of ~50ish files Something like: *csplit -k myfile.xml '/</listing>/' 25000 {50} Any help would be great Thanks!

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• Are application servers necessary? Advantages of using one? (And other JEE questions)

  - by Mike

  Apologies for the long question.. there seems to be other similar questions on here but none really clear up my confusion. I'd be really grateful if someone could confirm or correct my understanding: Java Enterprise Edition is a set of APIs for building enterprise applications, which take away the burden of developing parts of the system that aren't actually features of the application you are trying to build (i.e. messaging, transactions etc). To do this, you can use an application server, which implements these APIs. So you could use JBoss, Glassfish, WebSphere, WebLogic etc which would provide your application with these enterprise services. However, there are many other implementations of these individual services available such as ActiveMQ for messaging, Hibernate for persistence, OpenEJB etc. You can download these implementations as Java libraries and include them in your application, and use the services they provide in a similar way to using the services provided by an application server. So if my understanding is correct, my questions are: I've read a lot of places that application servers are necessary for JEE features like EJB, but can't you just use an implementation such as OpenEJB and not need an application server at all? Are there any features that an application server provides which you cannot get from another source? Why would/wouldn't I choose an application server over a custom stack such as Tomcat, OpenEJB, ActiveMQ, and Hibernate? Is Spring a complete alternative to JEE? Does it ever require an application server or always just a servlet container? Why would someone choose Spring over JEE? Any help would be much appreciated!

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• Cannot overload function

  - by anio

  So I've got a templatized class and I want to overload the behavior of a function when I have specific type, say char. For all other types, let them do their own thing. However, c++ won't let me overload the function. Why can't I overload this function? I really really do not want to do template specialization, because then I've got duplicate the entire class. Here is a toy example demonstrating the problem: http://codepad.org/eTgLG932 The same code posted here for your reading pleasure: #include <iostream> #include <cstdlib> #include <string> struct Bar { std::string blah() { return "blah"; } }; template <typename T> struct Foo { public: std::string doX() { return m_getY(my_t); } private: std::string m_getY(char* p_msg) { return std::string(p_msg); } std::string m_getY(T* p_msg) { return p_msg->blah(); } T my_t; }; int main(int, char**) { Foo<char> x; Foo<Bar> y; std::cout << "x " << x.doX() << std::endl; return EXIT_SUCCESS; } Thank you everyone for your suggestions. Two valid solutions have been presented. I can either specialize the doX method, or specialize m_getY() method. At the end of the day I prefer to keep my specializations private rather than public so I'm accepting Krill's answer.

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• Return lines in input code causing gaps/whitespace between elements in output?

  - by Jenny Zhang

  I am trying to put images next to each other on a webpage. Here is my HTML: <img class="pt" src="Yellow Tulip.jpg" title="Yellow Tulip" alt="Yellow Tulip" /> <img class="pt" src="Pink Tulip.jpg" title="Pink Tulip" alt="Pink Tulip" /> <img class="pt" src="Purple Tulip.jpg" title="Purple Tulip" alt="Purple Tulip" /> However, on my webpage, this shows a gap between each image. I've noticed that once I remove the return line that makes the elements separate and readable and instead just put all the elements on one line, the gaps go away. <img class="pt" src="Yellow Tulip.jpg" title="Yellow Tulip" alt="Yellow Tulip" /><img class="pt" src="Pink Tulip.jpg" title="Pink Tulip" alt="Pink Tulip" /><img class="pt" src="Purple Tulip.jpg" title="Purple Tulip" alt="Purple Tulip" /> Is there anyway I can achieve the output of the latter but still have the code/input look like the former? I really like the readability that the return lines (enter spaces) bring to the code, but I don't want the whitespace it creates on the actual page. If someone could explain why this is and/or how to fix it, I'd be really grateful! :)

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• Glassfish: Storing Java classes in the docroot folder?

  - by Tom Marthenal

  I'm very new to using Glassfish or JSP. I have this working in NetBeans (which has Glassfish bundled) but when I try to put it on my server which is running Glassfish Server, I really don't know what I'm doing. I can place a JSP file in "domains/domain1/docroot/index.jsp" and it will work when I visit my site, but I can't, for some reason, get Java classes to work. I copied the files in "/build/web/" from the NetBeans project to the docroot folder on my server. The errors I get when I visit the site are: org.apache.jasper.JasperException: PWC6033: Error in Javac compilation for JSP PWC6199: Generated servlet error: string:///index_jsp.java:7: package test does not exist PWC6197: An error occurred at line: 5 in the jsp file: /index.jsp PWC6199: Generated servlet error: string:///index_jsp.java:52: cannot find symbol symbol : class TestClass location: class org.apache.jsp.index_jsp PWC6197: An error occurred at line: 5 in the jsp file: /index.jsp PWC6199: Generated servlet error: string:///index_jsp.java:52: cannot find symbol symbol : class TestClass location: class org.apache.jsp.index_jsp The actual Java class is in "WEB-INF/classes/test/TestClass.class" (it is pre-compiled). I really have no idea what I'm doing wrong so any help is greatly appreciated. Thanks!

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• Open closed prinicple, problem

  - by Marcus

  Hi, I'm trying to apply OCP to a code snippet I have that in it's current state is really smelly, but I feel I'm not getting all the way to the end. Current code: public abstract class SomeObject {} public class SpecificObject1 : SomeObject {} public class SpecificObject2 : SomeObject {} // Smelly code public class Model { public void Store(SomeObject someObject) { if (someObject is SpecificObject1) {} else if (someObject is SpecificObject2) {} } } That is really ugly, my new approach looks like this: // No so smelly code public class Model { public void Store(SomeObject someObject) { throw new Expception("Not allowed!"); } public void Store(SpecificObject1 someObject) {} public void Store(SpecificObject2 someObject) {} } When a new SomeObject type comes along I must implement how that specific object is stored, this will break OCP cause I need to alter the Model-class. To move the store logic to SomeObject also feels wrong cause then I will violate SRP (?), becuase in this case the SomeObject is almost like a DTO, it's resposibility it not how to know to store itself. If a new implementation to SomeObject comes along who's store implementation is missing I will get a runtime error due to exception in Store method in Model class, it also feels like a code smell. This is because calling code will in the form of IEnumerable<SomeObject> sequence; I will not know the specific types of the sequence objects. I can't seem to grasp the OCP-concept. Anyone has any concrete examples or links that is a bit more than just some Car/Fruit example?

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• Java - Calling all methods of a class

  - by Thomas Eschemann

  I'm currently working on an application that has to render several Freemarker templates. So far I have a Generator class that handles the rendering. The class looks more or less like this: public class Generator { public static void generate(…) { renderTemplate1(); renderTemplate2(); renderTemplate3(); } private static void render(…) { // renders the template } private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; … } This works, but it doesn't really feel right. What I would like to do is create a class that holds all the renderTemplate...() methods and then call them dynamically from my Generator class. This would make it cleaner and easier to extend. I was thinking about using something like reflection, but it doesn't really feel like a good solution either. Any idea on how to implement this properly ?

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• Compare system date with a date field in SQL

  - by JeT_BluE

  I am trying to compare a date record in SQL Server with the system date. In my example the user first register with his name and date of birth which are then stored in the database. The user than logs into the web application using his name only. After logging in, his name is shown on the side where it says "Welcome "player name" using Sessions. What I am trying to show in addition to his name is a message saying "happy birthday" if his date of birth matches the system date. I have tried working with System.DateTime.Now, but what I think is that it is also comparing the year, and what I really want is the day and the month only. I would really appreciate any suggestion or help. CODE In Login page: protected void Button1_Click(object sender, EventArgs e) { String name = TextBox1.Text; String date = System.DateTime.Today.ToShortDateString(); SqlConnection myconn2 = new SqlConnection(ConfigurationManager.ConnectionStrings["User"].ToString()); SqlCommand cmd2 = new SqlCommand(); SqlDataReader reader; myconn2.Open(); cmd2 = new SqlCommand("Select D_O_B from User WHERE Username = @username", myconn2); cmd2.Parameters.Add("@username", SqlDbType.NVarChar).Value = name; cmd2.Connection = myconn2 cmd2.ExecuteNonQuery(); reader = cmd2.ExecuteReader(); while (reader.Read().ToString() == date) { Session["Birthday"] = "Happy Birthday"; } } Note: I using the same reader in the code above this one, but the reader here is with a different connection. Also, reader.Read() is different than reader.HasRows? Code in Web app Page: string date = (string)(Session["Birthday"]); // Retrieving the session Label6.Text = date;

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• Licensing for the undecided

  - by Jasper

  I am creating a game in C++. Now I am not sure on how I will distribute it yet - though I am pretty sure that I won't be asking money for it. And I am looking into a licensing and I wondered if there is a license that is suited for the undecided like me. My current releases (which are really really early versions of the game, with far from full functionality) are executable only. However, I am actually thinking that I might release the source on an open source license. For now, I am the only contributor, so that would be no problem as I only need my own permission to move to a less restrictive license. However, when I allow other people to contribute, I would need all their permissions to do so (right?). So I was wondering if there is a license that let's me distribute the game executable only for now, but will let me switch to a less restrictive license if I want. Basically I need a license in which contributors give permission to switch to a less restrictive license up front. Does anybody know of license (or other construction) that would allow me to do so?

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• When to use @Singleton in a Jersey resource

  - by dexter

  I have a Jersey resource that access the database. Basically it opens a database connection in the initialization of the resource. Performs queries on the resource's methods. I have observed that when I do not use @Singleton, the database is being open at each request. And we know opening a connection is really expensive right? So my question is, should I specify that the resource be singleton or is it really better to keep it at per request especially when the resource is connecting to the database? My resource code looks like this: //Use @Singleton here or not? @Path(/myservice/) public class MyResource { private ResponseGenerator responser; private Log logger = LogFactory.getLog(MyResource.class); public MyResource() { responser = new ResponseGenerator(); } @GET @Path("/clients") public String getClients() { logger.info("GETTING LIST OF CLIENTS"); return responser.returnClients(); } ... // some more methods ... } And I connect to the database using a code similar to this: public class ResponseGenerator { private Connection conn; private PreparedStatement prepStmt; private ResultSet rs; public ResponseGenerator(){ Class.forName("org.h2.Driver"); conn = DriverManager.getConnection("jdbc:h2:testdb"); } public String returnClients(){ String result; try{ prepStmt = conn.prepareStatement("SELECT * FROM hosts"); rs = prepStmt.executeQuery(); ... //do some processing here ... } catch (SQLException se){ logger.warn("Some message"); } finally { rs.close(); prepStmt.close(); // should I also close the connection here (in every method) if I stick to per request // and add getting of connection at the start of every method // conn.close(); } return result } ... // some more methods ... } Some comments on best practices for the code will also be helpful.

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• Saving a single entity instead of the entire context - revisited

  - by nite

  I’m looking for a way to have fine grained control over what is saved using Entity Framework, rather than the whole ObjectContext.SaveChanges(). My scenario is pretty straight forward, and I’m quite amazed not catered for in EF – pretty basic in NHibernate and all other data access paradigms I’ve seen. I’m generating a bunch of data (in a WPF UI) and allowing the user to fine tune what is proposed and choose what is actually committed to the database. For the proposed entities I’m: getting a bunch of reference entities (eg languages) via my objectcontext, creating the proposed entities and assigning these reference entities to them (as navigation properties), so by virtue of their relationship to the reference entities they’re implicitly added to the objectconext Trying to create & save individual entites based on the proposed entities. I figure this should be really simple & trivial but everything I’ve tried I’ve hit a brick wall, either I set up another objectcontext & add just the entity I need (it then tries to add the whole graph and fails as it’s on another objectcontext). I’ve tried MergeOptions = NoTracking on my reference entities to try to get the Attach/AddObject not to navigate through these to create a graph, no avail. I've removed the navigation properties from the reference entities. I've tried AcceptAllChanges, that works but pretty useless in practice as I do still want to track & save other entities. In a simple test, I can create 2 of my proposed entities, AddObject the one I want to save and then Detach the one I dont then call SaveChanges, this works but again not great in practice. Following are a few links to some of the nifty ideas which in the end don’t help in the end but illustrate the complexity of EF for something so simple. I’m really looking for a SaveSingle/SaveAtomic method, and think it’s a pretty reasonable & basic ask for any DAL, letalone a cutting edge ORM. http://stackoverflow.com/questions/1301460/saving-a-single-entity-instead-of-the-entire-context www.codeproject.com/KB/architecture/attachobjectgraph.aspx?fid=1534536&df=90&mpp=25&noise=3&sort=Position&view=Quick&select=3071122&fr=1 bernhardelbl.spaces.live.com/blog/cns!DB54AE2C5D84DB78!238.entry

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• "Most popular" GROUP BY in LINQ?

  - by tags2k

  Assuming a table of tags like the stackoverflow question tags: TagID (bigint), QuestionID (bigint), Tag (varchar) What is the most efficient way to get the 25 most used tags using LINQ? In SQL, a simple GROUP BY will do: SELECT Tag, COUNT(Tag) FROM Tags GROUP BY Tag I've written some LINQ that works: var groups = from t in DataContext.Tags group t by t.Tag into g select new { Tag = g.Key, Frequency = g.Count() }; return groups.OrderByDescending(g => g.Frequency).Take(25); Like, really? Isn't this mega-verbose? The sad thing is that I'm doing this to save a massive number of queries, as my Tag objects already contain a Frequency property that would otherwise need to check back with the database for every Tag if I actually used the property. So I then parse these anonymous types back into Tag objects: groups.OrderByDescending(g => g.Frequency).Take(25).ToList().ForEach(t => tags.Add(new Tag() { Tag = t.Tag, Frequency = t.Frequency })); I'm a LINQ newbie, and this doesn't seem right. Please show me how it's really done.

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• Is there a way to load an existing connection string for Linq to SQL from an app.config file?

  - by Brian Surowiec

  I'm running into a really annoying problem with my Linq to SQL project. When I add everything in under the web project everything goes as expected and I can tell it to use my existing connection string stored in the web.config file and the Linq code pulls directly from the ConfigurationManager. This all turns ugly once I move the code into its own project. I’ve created an app.config file, put the connection string in there as it was in the web.config but when I try to add another table in the IDE keeps forcing me to either hardcode the connection string or creates a Settings file and puts it in there, which then adds a new entry into the app.config file with a new name. Is there a way keep my Linq code in its own project yet still refer back to my config file without the IDE continuously hardcoding the connection string or creating the Settings file? I’m converting part of my DAL over to use Linq to SQL so I’d like to use the existing connection string that our old code is using as well as keep the value in a common location, and one spot, instead of in a number of spots. Manually changing the mode to WebSettings instead of AppSettings works untill I try to add a new table, then it goes back to hardcoding the value or recreating the Settings file. I also tried to switch the project type to be a web project and then rename my app.config to web.config and then everything works as I’d like it to. I’m just not sure if there are any downfalls to keeping this as a web project since it really isn't one. The project only contains the Linq to SQL code and an implementation of my repository classes. My project layout looks like this Website -connectionString.config -web.config (refers to connectionString.config) Middle Tier -Business Logic -Repository Interfaces -etc. DAL -Linq to SQL code -Existing SPROC code -connectionString.config (linked from the web poject) -app.config (refers to connectionString.config)

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• Java reflection appropriateness

  - by jsn

  This may be a fairly subjective question, but maybe not. My application contains a bunch of forms that are displayed to the user at different times. Each form is a class of its own. Typically the user clicks a button, which launches a new form. I have a convenience function that builds these buttons, you call it like this: buildButton( "button text", new SelectionAdapter() { @Override public void widgetSelected( SelectionEvent e ) { showForm( new TasksForm( args... ) ); } } ); I do this dozens of times, and it's really cumbersome having to make a SelectionAdapter every time. Really all I need for the button to know is what class to instantiate when it's clicked and what arguments to give the constructor, so I built a function that I call like this instead: buildButton( "button text", TasksForm.class, args... ); Where args is an arbitrary list of objects that you could use to instantiate TasksForm normally. It uses reflection to get a constructor from the class, match the argument list, and build an instance when it needs to. Most of the time I don't have to pass any arguments to the constructor at all. The downside is obviously that if I'm passing a bad set of arguments, it can't detect that at compilation time, so if it fails, a dialog is displayed at runtime. But it won't normally fail, and it'll be easy to debug if it does. I think this is much cleaner because I come from languages where the use of function and class literals is pretty common. But if you're a normal Java programmer, would seeing this freak you out, or would you appreciate not having to scan a zillion SelectionAdapters?

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