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• Adaptive Connections For ADFBC

  - by Duncan Mills

  Some time ago I wrote an article on Adaptive Bindings showing how the pageDef for a an ADF UI does not have to be wedded to a fixed data control or collection / View Object. This article has proved pretty popular, so as a follow up I wanted to cover another "Adaptive" feature of your ADF applications, the ability to make multiple different connections from an Application Module, at runtime. Now, I'm sure you'll be aware that if you define your application to use a data-source rather than a hard-coded JDBC connection string, then you have the ability to change the target of that data-source after deployment to point to a different database. So that's great, but the reality of that is that this single connection is effectively fixed within the application right?  Well no, this it turns out is a common misconception. To be clear, yes a single instance of an ADF Application Module is associated with a single connection but there is nothing to stop you from creating multiple instances of the same Application Module within the application, all pointing at different connections.  If fact this has been possible for a long time using a custom extension point with code that which extends oracle.jbo.http.HttpSessionCookieFactory. This approach, however, involves writing code and no-one likes to write any more code than they need to, so, is there an easier way? Yes indeed.  It is in fact  a little publicized feature that's available in all versions of 11g, the ELEnvInfoProvider. What Does it Do?  The ELEnvInfoProvider  is  a pre-existing class (the full path is  oracle.jbo.client.ELEnvInfoProvider) which you can plug into your ApplicationModule configuration using the jbo.envinfoprovider property. Visuallty you can set this in the editor, or you can also set it directly in the bc4j.xcfg (see below for an example) . Once you have plugged in this envinfoprovider, here's the fun bit, rather than defining the hard-coded name of a datasource instead you can plug in a EL expression for the connection to use.  So what's the benefit of that? Well it allows you to defer the selection of a connection until the point in time that you instantiate the AM. To define the expression itself you'll need to do a couple of things: First of all you'll need a managed bean of some sort – e.g. a sessionScoped bean defined in your ViewController project. This will need a getter method that returns the name of the connection. Now this connection itself needs to be defined in your Application Server, and can be managed through Enterprise Manager, WLST or through MBeans. (You may need to read the documentation [http://docs.oracle.com/cd/E28280_01/web.1111/b31974/deployment_topics.htm#CHDJGBDD] here on how to configure connections at runtime if you're not familiar with this)   The EL expression (e.g. ${connectionManager.connection} is then defined in the configuration by editing the bc4j.xcfg file (there is a hyperlink directly to this file on the configuration editing screen in the Application Module editor). You simply replace the hardcoded JDBCName value with the expression.  So your cfg file would end up looking something like this (notice the reference to the ELEnvInfoProvider that I talked about earlier) <BC4JConfig version="11.1" xmlns="http://xmlns.oracle.com/bc4j/configuration">   <AppModuleConfigBag ApplicationName="oracle.demo.model.TargetAppModule">   <AppModuleConfig DeployPlatform="LOCAL"  JDBCName="${connectionManager.connection}" jbo.project="oracle.demo.model.Model" name="TargetAppModuleLocal" ApplicationName="oracle.demo.model.TargetAppModule"> <AM-Pooling jbo.doconnectionpooling="true"/> <Database jbo.locking.mode="optimistic">       <Security AppModuleJndiName="oracle.demo.model.TargetAppModule"/>    <Custom jbo.envinfoprovider="oracle.jbo.client.ELEnvInfoProvider"/> </AppModuleConfig> </AppModuleConfigBag> </BC4JConfig> Still Don't Quite Get It? So far you might be thinking, well that's fine but what difference does it make if the connection is resolved "just in time" rather than up front and changed as required through Enterprise Manager? Well a trivial example would be where you have a single application deployed to your application server, but for different users you want to connect to different databases. Because, the evaluation of the connection is deferred until you first reference the AM you have a decision point that can take the user identity into account. However, think about it for a second.  Under what circumstances does a new AM get instantiated? Well at the first reference of the AM within the application yes, but also whenever a Task Flow is entered -  if the data control scope for the Task Flow is ISOLATED.  So the reality is, that on a single screen you can embed multiple Task Flows, all of which are pointing at different database connections concurrently. Hopefully you'll find this feature useful, let me know... 

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• Spring Security: session expiration without redirect to expired-url?

  - by Kdeveloper

  I'm using Spring Security 3.0.2 form based authentication. But I can't figure out how I can configure it so that when a session expires that the request is not redirect to an other page (expired-url) or displays a 'session expires' message. I don't want any redirect or messages, I want that a anonymous session is started just like when a user without a session enters the website. My current configuration: <http> <intercept-url pattern="/login.action*" filters="none"/> <intercept-url pattern="/admin/**" access="ROLE_ADMIN" /> <intercept-url pattern="/**" access="IS_AUTHENTICATED_ANONYMOUSLY"/> <form-login login-page="/login.action" authentication-failure-url="/login.action?error=failed" login-processing-url="/login-handler.action"/> <logout logout-url="/logoff-execute.action" logout-success-url="/logoff.action?done=1"/> <remember-me key="remember-me-security" services-ref="rememberMeServices"/> <session-management > <concurrency-control max-sessions="1" error-if-maximum-exceeded="false" expired-url="/login.action?error=expired.url"/> </session-management> </http>

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• EF 4, POCO and AddOrUpdate

  - by Eric J.

  I'm trying to create a method on an EF 4 POCO repository called AddOrUpdate. The idea is that the business layer can pass in a POCO object and the persistence framework will add the object if it is new (not yet in the database), else will update the database (once SaveChanges() is called) with the new value. This is similar to some other questions I have asked about EF, but I'm only about 80% there in understanding this so please forgive partial duplication. The part I'm missing is how to update the object graph in my ObjectContext/associated ObjectSet for the passed-in business object once I have determined that the business object indeed already exists in the database (and now has been loaded thanks to TryGetObjectByKey). ApplyCurrentValues sounds sort of like what I want, but it only copies scalar values and doesn't seem intended to update the object graph in the ObjectContext/ObjectSet. Because of my particular use case I don't care about concurrency right now. public void AddOrUpdate(BO biz) { object obj; EntityKey ek = Ctx.CreateEntityKey(mySetName, biz); bool found = Ctx.TryGetObjectByKey(ek, out obj); if (found) { // How do I do what this method name implies? Biz is a parent with children. mySet.TellTheSetToUpdateThisObject(biz); } else { mySet.AddObject(biz); } Ctx.DetectChanges(); }

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• How can I beta test web Perl modules under Apache/mod_perl on production web server?

  - by DVK

  We have a setup where most code, before being promoted to full production, is deployed in BETA mode - meaning, it runs in full production environment (using production database - usually production data; and production web server). We call that stage BETA testing. One of the main requirements is that BETA code promotion to production must be a simple "cp" command from beta to production directory - no code/filename changes. For non-web Perl code, achieving seamless BETA test is quite doable (see details here): Perl programs live in a standard location under production root (/usr/code/scripts) with production perl modules living under the same root (/usr/code/lib/perl) The BETA code has 100% same code paths except under beta root (/usr/code/beta/) A special module manipulates @INC of any script based on whether the script was called from /usr/code/scripts or /usr/code/test/scripts, to include beta libraries for beta scripts. This setup works fine up till we need to beta test our web Perl code (the setup is EmbPerl and Apache/mod_perl). The hang-up is as follows: if both a production Perl module and BETA Perl module have the same name (e.g. /usr/code/lib/perl/MyLib1.pm and /usr/code/beta/lib/perl/MyLib1.pm), then mod_perl will only be able to load ONE of these modules into memory - and there's no way we are aware of for a particular web page to affect which version of the module is currently loaded due to concurrency issues. Leaving aside the obvious non-programming solution (get a bloody BETA web server) which for political/organizational reasons is not feasible, is there any way we can somehow hack around this problem in either Perl or mod_perl? I played around with various approaches to unloading Perl modules that %INC has listed, but the problem remains that another user might load a beta page at just the right (or rather wrong) moment and have the beta module loaded which will be used for my production page.

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• Atomic UPSERT in SQL Server 2005

  - by rabidpebble

  What is the correct pattern for doing an atomic "UPSERT" (UPDATE where exists, INSERT otherwise) in SQL Server 2005? I see a lot of code on SO (e.g. see http://stackoverflow.com/questions/639854/tsql-check-if-a-row-exists-otherwise-insert) with the following two-part pattern: UPDATE ... FROM ... WHERE <condition> -- race condition risk here IF @@ROWCOUNT = 0 INSERT ... or IF (SELECT COUNT(*) FROM ... WHERE <condition>) = 0 -- race condition risk here INSERT ... ELSE UPDATE ... where will be an evaluation of natural keys. None of the above approaches seem to deal well with concurrency. If I cannot have two rows with the same natural key, it seems like all of the above risk inserting rows with the same natural keys in race condition scenarios. I have been using the following approach but I'm surprised not to see it anywhere in people's responses so I'm wondering what is wrong with it: INSERT INTO <table> SELECT <natural keys>, <other stuff...> FROM <table> WHERE NOT EXISTS -- race condition risk here? ( SELECT 1 FROM <table> WHERE <natural keys> ) UPDATE ... WHERE <natural keys> (Note: I'm assuming that rows will not be deleted from this table. Although it would be nice to discuss how to handle the case where they can be deleted -- are transactions the only option? Which level of isolation?) Is this atomic? I can't locate where this would be documented in SQL Server documentation.

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• Suggestions for doing async I/O with Task Parallel Library

  - by anelson

  I have some high performance file transfer code which I wrote in C# using the Async Programming Model (APM) idiom (eg, BeginRead/EndRead). This code reads a file from a local disk and writes it to a socket. For best performance on modern hardware, it's important to keep more than one outstanding I/O operation in flight whenever possible. Thus, I post several BeginRead operations on the file, then when one completes, I call a BeginSend on the socket, and when that completes I do another BeginRead on the file. The details are a bit more complicated than that but at the high level that's the idea. I've got the APM-based code working, but it's very hard to follow and probably has subtle concurrency bugs. I'd love to use TPL for this instead. I figured Task.Factory.FromAsync would just about do it, but there's a catch. All of the I/O samples I've seen (most particularly the StreamExtensions class in the Parallel Extensions Extras) assume one read followed by one write. This won't perform the way I need. I can't use something simple like Parallel.ForEach or the Extras extension Task.Factory.Iterate because the async I/O tasks don't spend much time on a worker thread, so Parallel just starts up another task, resulting in potentially dozens or hundreds of pending I/O operations; way too much! You can work around that by Waiting on your tasks, but that causes creation of an event handle (a kernel object), and a blocking wait on a task wait handle, which ties up a worker thread. My APM-based implementation avoids both of those things. I've been playing around with different ways to keep multiple read/write operations in flight, and I've managed to do so using continuations that call a method that creates another task, but it feels awkward, and definitely doesn't feel like idiomatic TPL. Has anyone else grappled with an issue like this with the TPL? Any suggestions?

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• WinForms DataGridView - update database

  - by Geo Ego

  I know this is a basic function of the DataGridView, but for some reason, I just can't get it to work. I just want the DataGridView on my Windows form to submit any changes made to it to the database when the user clicks the "Save" button. I populate the DataGridView according to a function triggered by a user selection in a DropDownList as follows: using (SqlConnection con = new SqlConnection(conString)) { con.Open(); SqlDataAdapter ruleTableDA = new SqlDataAdapter("SELECT rule.fldFluteType AS [Flute], rule.fldKnife AS [Knife], rule.fldScore AS [Score], rule.fldLowKnife AS [Low Knife], rule.fldMatrixScore AS [Matrix Score], rule.fldMatrix AS [Matrix] FROM dbo.tblRuleTypes rule WHERE rule.fldMachine_ID = '1003'", con); DataSet ruleTableDS = new DataSet(); ruleTableDA.Fill(ruleTableDS); RuleTable.DataSource = ruleTableDS.Tables[0]; } In my save function, I basically have the following (I've trimmed out some of the code around it to get to the point): using (SqlDataAdapter ruleTableDA = new SqlDataAdapter("SELECT rule.fldFluteType AS [Flute], rule.fldKnife AS [Knife], rule.fldScore AS [Score], rule.fldLowKnife AS [Low Knife], rule.fldMatrixScore AS [Matrix Score], rule.fldMatrix AS [Matrix] FROM dbo.tblRuleTypes rule WHERE rule.fldMachine_ID = '1003'", con)) { SqlCommandBuilder commandBuilder = new SqlCommandBuilder(ruleTableDA); DataTable dt = new DataTable(); dt = RuleTable.DataSource as DataTable; ruleTableDA.Fill(dt); ruleTableDA.Update(dt); } Okay, so I edited the code to do the following: build the commands, create a DataTable based on the DataGridView (RuleTable), fill the DataAdapter with the DataTable, and update the database. Now ruleTableDA.Update(dt) is throwing the exception "Concurrency violation: the UpdateCommand affected 0 of the expected 1 records."

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• Can I tell Castle Windsor to create a component in a separate AppDomain?

  - by Michael L Perry

  I've created a multi-threaded service that uses Castle Windsor to create components to run on separate threads. I Resolve an component by name with parameters for each thread. I'm running into concurrency problems with a 3rd party library used by the components. I suspect that isolating those components in separate AppDomains will resolve the problem. Is there a way to have Resolve create the component using a different AppDomain? private ActivityThread NewActivityThread(ActivityInstance activityInstance) { // Set up the creation arguments. System.Collections.IDictionary arguments = new Dictionary<string, string>(); activityInstance.Parameters.ForEach(p => arguments.Add(p.Name, p.Value)); // Get the activity handler from the container. IActivity activity = Program.Container.Resolve<IActivity>(activityInstance.Name, arguments); // Create a thread for the activity. ActivityThread thread = new ActivityThread(activity, activityInstance, _nextActivityID++); return thread; } public ActivityThread(IActivity activity, ActivityInstance instance, int id) { _activity = activity; _instance = instance; _id = id; } public void Start() { if (_thread == null) { // Create a new thread to run this activity. _thread = new Thread(delegate() { _activity.Run(); }); _thread.Name = _activity.ToString(); _thread.SetApartmentState(ApartmentState.STA); _thread.Start(); } }

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• Implementation review for a MVC.NET app with custom membership

  - by mrjoltcola

  I'd like to hear if anyone sees any problems with how I implemented the security in this Oracle based MVC.NET app, either security issues, concurrency issues or scalability issues. First, I implemented a CustomOracleMembershipProvider to handle the database interface to the membership store. I implemented a custom Principal named User which implements IPrincipal, and it has a hashtable of Roles. I also created a separate class named AuthCache which has a simple cache for User objects. Its purpose is simple to avoid return trips to the database, while decoupling the caching from either the web layer or the data layer. (So I can share the cache between MVC.NET, WCF, etc.) The MVC.NET stock MembershipService uses the CustomOracleMembershipProvider (configured in web.config), and both MembershipService and FormsService share access to the singleton AuthCache. My AccountController.LogOn() method: 1) Validates the user via the MembershipService.Validate() method, also loads the roles into the User.Roles container and then caches the User in AuthCache. 2) Signs the user into the Web context via FormsService.SignIn() which accesses the AuthCache (not the database) to get the User, sets HttpContext.Current.User to the cached User Principal. In global.asax.cs, Application_AuthenticateRequest() is implemented. It decrypts the FormsAuthenticationTicket, accesses the AuthCache by the ticket.Name (Username) and sets the Principal by setting Context.User = user from the AuthCache. So in short, all these classes share the AuthCache, and I have, for thread synchronization, a lock() in the cache store method. No lock in the read method. The custom membership provider doesn't know about the cache, the MembershipService doesn't know about any HttpContext (so could be used outside of a web app), and the FormsService doesn't use any custom methods besides accessing the AuthCache to set the Context.User for the initial login, so it isn't dependent on a specific membership provider. The main thing I see now is that the AuthCache will be sharing a User object if a user logs in from multiple sessions. So I may have to change the key from just UserId to something else (maybe using something in the FormsAuthenticationTicket for the key?).

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• Ruby - Immutable Objects

  - by Chris Bunch

  I've got a highly multithreaded app written in Ruby that shares a few instance variables. Writes to these variables are rare (1%) while reads are very common (99%). What is the best way (either in your opinion or in the idiomatic Ruby fashion) to ensure that these threads always see the most up-to-date values involved? Here's some ideas so far that I had (although I'd like your input before I overhaul this): Have a lock that most be used before reading or writing any of these variables (from Java Concurrency in Practice). The downside of this is that it puts a lot of synchronize blocks in my code and I don't see an easy way to avoid it. Use Ruby's freeze method (see here), although it looks equally cumbersome and doesn't give me any of the synchronization benefits that the first option gives. These options both seem pretty similar but hopefully anyone out there will have a better idea (or can argue well for one of these ideas). I'd also be fine with making the objects immutable so they aren't corrupted or altered in the middle of an operation, but I don't know Ruby well enough to make the call on my own and this question seems to argue that objects are highly mutable.

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• Updating multiple related tables in SQLite

  - by PerryJ

  Just some background, sorry so long winded. I'm using the System.Data.SQLite ADO.net adapter to create a local sqlite database and this will be the only process hitting the database, so I don't need to worry about concurrency. I'm building the database from various sources and don't want to build this all in memory using datasets or dataadapters or anything like that. I want to do this using SQL (DdCommands). I'm not very good with SQL and complete noob in sqlite. I'm basically using sqlite as a local database / save file structure. The database has a lot of related tables and the data has nothing to do with People or Regions or Districts, but to use a simple analogy, imagine: Region table with auto increment RegionID, RegionName column and various optional columns. District table with auto increment DistrictID, DistrictName, RegionId, and various optional columns Person table with auto increment PersonID, PersonName, DistrictID, and various optional columns So I get some data representing RegionName, DistrictName,PersonName, and other Person related data. The Region, District and/or Person may or may not be created at this point. Once again, not being the greatest with this, my thoughts would be something like: Check to see if Region exists and if so get the RegionID else create it and get RegionID Check to see if District exists and if so get the DistrictID else create it adding in RegionID from above and get DistrictID Check to see if Person exists and if so get the PersonID else create it adding in DistrictID from above and get PersonID Update Person with rest of data. In MS SQL Server I would create a stored procedure to handle all this. Only way I can see to do this with sqlite is a lot of commands. So I'm sure I'm not getting this. I've spent hours looking around on various sites but just don't feel like I'm going down the right road. Any suggestions would be greatly appreciated.

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• Retrieve input entered in a JDialog

  - by Jules Olléon

  I extended JDialog to create a custom dialog where the user must fill some fields : How should I retrieve the data entered ? I came up with a solution that works. It mimics JOptionPane but the way I do it looks ugly to me because of the static fields involved... Here is roughly my code : public class FObjectDialog extends JDialog implements ActionListener { private static String name; private static String text; private JTextField fName; private JTextArea fText; private JButton bAdd; private JButton bCancel; private FObjectDialog(Frame parentFrame) { super(parentFrame,"Add an object",true); // build the whole dialog buildNewObjectDialog(); setVisible(true); } @Override public void actionPerformed(ActionEvent ae) { if(ae.getSource()==bAdd){ name=fName.getText(); text=fText.getText(); } else { name=null; text=null; } setVisible(false); dispose(); } public static String[] showCreateDialog(Frame parentFrame){ new FObjectDialog(parentFrame); String[] res={name,text}; if((name==null)||(text==null)) res=null; return res; } } As I said, that works properly, but I guess that might raise serious concurrency issues... Is there a cleaner way to do that ? How is it done in JOptionPane ?

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• Execute remote Lua Script

  - by Bruno Lee

  Hi, I want to make an application that executes a remote script. The user can create a script (probabily a LUA script) then stores it in the server. Then he can uses an API for execute the script. I was thinking that API could be a webservice. So my questions are: I need high performance to execute the script. So my first choice was LUA script. Someone has another sugestion? Cause I need high perfomance, I was thinking if the webservice is the best solution. Maybe I could create a TCP/IP Windows Service that hold the users request. It is important to say that I will have many user executing scripts at the same time. So I will have a concurrency problem. My scripts will query in a database. I will use Tokyo Cabinet or Tokio Tyrant. I think Tokio Tyrant is the only solution cause I will have many requests. For perfomance, Do I need to make a connection pooling? Is there anyway to share variables between webservices requests? To make the webservice or the Windows service i was thinking to use C++. Can someone help with these questions? thanks

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• Using StringBuilder to process csv files to save heap space

  - by portoalet

  I am reading a csv file that has about has about 50,000 lines and 1.1MiB in size (and can grow larger). In Code1, I use String to process the csv, while in Code2 I use StringBuilder (only one thread executes the code, so no concurrency issues) Using StringBuilder makes the code a little bit harder to read that using normal String class. Am I prematurely optimizing things with StringBuilder in Code2 to save a bit of heap space and memory? Code1 fr = new FileReader(file); BufferedReader reader = new BufferedReader(fr); String line = reader.readLine(); while ( line != null ) { int separator = line.indexOf(','); String symbol = line.substring(0, seperator); int begin = separator; separator = line.indexOf(',', begin+1); String price = line.substring(begin+1, seperator); // Publish this update publisher.publishQuote(symbol, price); // Read the next line of fake update data line = reader.readLine(); } Code2 fr = new FileReader(file); StringBuilder stringBuilder = new StringBuilder(reader.readLine()); while( stringBuilder.toString() != null ) { int separator = stringBuilder.toString().indexOf(','); String symbol = stringBuilder.toString().substring(0, separator); int begin = separator; separator = stringBuilder.toString().indexOf(',', begin+1); String price = stringBuilder.toString().substring(begin+1, separator); publisher.publishQuote(symbol, price); stringBuilder.replace(0, stringBuilder.length(), reader.readLine()); }

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• How do people know so much about programming?

  - by Luciano

  I see people in this forums with a lot of points, so I assume they know about a lot of different programming stuff. When I was young I knew about basic (commodore) and the turbo pascal (pc). Then in college I learnt about C, memory management, x86 set, loop invariants, graphs, db query optimization, oop, functional, lambda calculus, prolog, concurrency, polymorphism, newton method, simplex, backtracking, dynamic programming, heuristics, np completeness, LR, LALR, neural networks, static & dynamic typing, turing, godel, and more in between. Then in industry I started with Java several years ago and learnt about it, and its variety of frameworks, and also design patterns, architecture patterns, web development, server development, mobile development, tdd, bdd, uml, use cases, bug trackers, process management, people management if you are a tech lead, profiling, security concerns, etc. I started to forget what I learnt in college... And then there is the stuff I don't know yet, like python, .net, perl, JVM stuff like groovy or scala.. Of course Google is a must for rapid documentation access to know if a problem has been solved already and how, and to keep informed about new stuff by blogs and places like this one. It's just too much or I just have a bad memory.. how do you guys manage it?

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• Updating multiple related tables in SQLite with C#

  - by PerryJ

  Just some background, sorry so long winded. I'm using the System.Data.SQLite ADO.net adapter to create a local sqlite database and this will be the only process hitting the database, so I don't need to worry about concurrency. I'm building the database from various sources and don't want to build this all in memory using datasets or dataadapters or anything like that. I want to do this using SQL (DdCommands). I'm not very good with SQL and complete noob in sqlite. I'm basically using sqlite as a local database / save file structure. The database has a lot of related tables and the data has nothing to do with People or Regions or Districts, but to use a simple analogy, imagine: Region table with auto increment RegionID, RegionName column and various optional columns. District table with auto increment DistrictID, DistrictName, RegionId, and various optional columns Person table with auto increment PersonID, PersonName, DistrictID, and various optional columns So I get some data representing RegionName, DistrictName,PersonName, and other Person related data. The Region, District and/or Person may or may not be created at this point. Once again, not being the greatest with this, my thoughts would be something like: Check to see if Region exists and if so get the RegionID else create it and get RegionID Check to see if District exists and if so get the DistrictID else create it adding in RegionID from above and get DistrictID Check to see if Person exists and if so get the PersonID else create it adding in DistrictID from above and get PersonID Update Person with rest of data. In MS SQL Server I would create a stored procedure to handle all this. Only way I can see to do this with sqlite is a lot of commands. So I'm sure I'm not getting this. I've spent hours looking around on various sites but just don't feel like I'm going down the right road. Any suggestions would be greatly appreciated.

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• How should I go about implementing a points-to analysis in Maude?

  - by reprogrammer

  I'm going to implement a points-to analysis algorithm. I'd like to implement this analysis mainly based on the algorithm by Whaley and Lam. Whaley and Lam use a BDD based implementation of Datalog to represent and compute the points-to analysis relations. The following lists some of the relations that are used in a typical points-to analysis. Note that D(w, z) :- A(w, x),B(x, y), C(y, z) means D(w, z) is true if A(w, x), B(x, y), and C(y, z) are all true. BDD is the data structure used to represent these relations. Relations input vP0 (variable : V, heap : H) input store (base : V, field : F, source : V) input load (base : V, field : F, dest : V) input assign (dest : V, source : V) output vP (variable : V, heap : H) output hP (base : H, field : F, target : H) Rules vP(v, h) :- vP0(v, h) vP(v1, h) :- assign(v1, v2), vP(v2, h) hP(h1, f,h2) :- store(v1, f, v2), vP(v1, h1), vP(v2, h2) vP(v2, h2) :- load(v1, f, v2), vP(v1, h1), hP(h1, f, h2) I need to understand if Maude is a good environment for implementing points-to analysis. I noticed that Maude uses a BDD library called BuDDy. But, it looks like that Maude uses BDDs for a different purpose, i.e. unification. So, I thought I might be able to use Maude instead of a Datalog engine to compute the relations of my points-to analysis. I assume Maude propagates independent information concurrently. And this concurrency could potentially make my points-to analysis faster than sequential processing of rules. But, I don't know the best way to represent my relations in Maude. Should I implement BDD in Maude myself, or Maude's internal unification based on BDD has the same effect?

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• Returning from dll (Asynchronous sockets)

  - by Juha

  I am trying to do a simple http-server in (c++) dll-file that I can use from managed (C#) application with P/Invoke. I was trying to do this with asynchronous functions (WSAAsyncSelect() and stuff), so that I could manage server by calling functions inside dll whenever needed and after that it would return to my main program. Now I'm not sure if that is even possible. It seems that "main function" in dll, the function that starts the server, has to include message loop or something and since it's a loop, it doesn't return from dll ever. Could I somehow do this message stuff in my managed application and call some function in dll when there is something to do? Or is it even possible to do this stuff in one thred? I would really like to avoid all concurrency stuff. The dll looks now basicly the same as here, main function is the one that I call from managed C# program and would like to return to there after calling the function. http://www.winsocketdotnetworkprogramming.com/winsock2programming/winsock2advancediomethod5b.html I'm quite noob in windows programming, and never even heard of this message-queue or message-loop.

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• Testing system where App-level and Request-level IoC containers exist

  - by Bobby

  My team is in the process of developing a system where we're using Unity as our IoC container; and to provide NHibernate ISessions (Units of work) over each HTTP Request, we're using Unity's ChildContainer feature to create a child container for each request, and sticking the ISession in there. We arrived at this approach after trying others (including defining per-request lifetimes in the container, but there are issues there) and are now trying to decide on a unit testing strategy. Right now, the application-level container itself is living in the HttpApplication, and the Request container lives in the HttpContext.Current. Obviously, neither exist during testing. The pain increases when we decided to use Service Location from our Domain layer, to "lazily" resolve dependencies from the container. So now we have more components wanting to talk to the container. We are also using MSTest, which presents some concurrency dilemmas during testing as well. So we're wondering, what do the bright folks out there in the SO community do to tackle this predicament? How does one setup an application that, during "real" runtime, relies on HTTP objects to hold the containers, but during test has the flexibility to build-up and tear-down the containers consistently, and have the ServiceLocation bits get to those precise containers. I hope the question is clear, thanks!

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• A business Case for Enterprise Python

  - by Srirangan

  Hi all, This will not be a "programming" question but more technology / platform related question. I'm trying to figure out whether Python can be a suitable Java alternative for enterprise / web applications. Which are the ideal cases where you would prefer to use Python instead of Java? How would a typical Python web application (databases/sessions/concurrency) perform as compared to a typical Java application? How do specific Python frameworks square up against Java based frameworks (Spring, SEAM, Grails etc.)? For businesses, switching from the Java infrastructure to a Python infrastructure .. is it too hard/expensive/resource intensive/not viable? Also shed some light on the business case for providing a Python + Google AppEngine based solution to the end customer. Will it be cost effective in an typical scenario? Sorry if I am asking too wide a question, I would have liked to keep it specific, but I need your help to evaluate Python as a whole from the perspectives of the programmers, service providing company and end business customer. For an SME, a Python/GoogleAppEngine based technology stack is a clear scalable and affordable platform. But what about a large MNC that already has a lot invested in Java. Thank you so much. I am researching this myself and will gladly share my conclusions here! Thank you, Srirangan

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• What specific features of LabView are frustrating to you?

  - by Underflow

  Please bear with me: this isn't a language debate or a flame. It's a real request for opinions. Occasionally, I have to help educate a traditional text coder in how to think in LabVIEW (LV). Often during this process, I get to hear about how LV sucks. Rarely is this insight accompanied by rational observations other than "Language X is just so much better!". While this statement is satisfying to them, it doesn't help me understand what is frustrating them. So, for those of you with LabVIEW and text language experience, what specific things about LV drive you nuts? ------ Summaries ------- Thanks for all the answers! Some of the issues are answered in the comments below, some exist on other sites, and some are just genuine problems with LV. In the spirit of the original question, I'm not going to try to answer all of these here: check LAVA or NI's website, and you'll be pleasantly surprised at how many of these things can be overcome. Unintentional concurrency No access to tradition text manipulation tools Binary-only source code control Difficult to branch and merge Too many open windows Text has cleaner/clearer/more expressive syntax Clean coding requires a lot of time and manipulation Large, difficult to access API/palette system Mouse required File namespacing: no duplicate files with the same name in memory LV objects are natively by-value only Requires dev environment to view code Lack of zoom Slow startup Memory pig "Giant" code is difficult to work with UI lockup is easy to do Trackpads and LV don't mix well String manipulation is graphically bloated Limited UI customization "Hidden" primitives (yes, these exist) Lack of official metaprogramming capability (not for much longer, though) Lack of unicode support [1]: http://www.lavag.org LAVA

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• Executing remote script - Architecture

  - by Bruno Lee

  Hi, I want to make an application that executes a remote script. The user can create a script (probabily a LUA script) then stores it in the server. Then he can uses an API for execute the script. I was thinking that API could be a webservice. So my questions are: I need high performance to execute the script. So my first choice was LUA script. Someone has another sugestion? Cause I need high perfomance, I was thinking if the webservice is the best solution. Maybe I could create a TCP/IP Windows Service that hold the users request. It is important to say that I will have many user executing scripts at the same time. So I will have a concurrency problem. My scripts will query in a database. I will use Tokyo Cabinet or Tokio Tyrant. I think Tokio Tyrant is the only solution cause I will have many requests. For perfomance, Do I need to make a connection pooling? Is there anyway to share variables between webservices requests? To make the webservice or the Windows service i was thinking to use C++. Can someone help with these questions? thanks

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• How to pass binary data between two apps using Content Provider?

  - by Viktor

  I need to pass some binary data between two android apps using Content Provider (sharedUserId is not an option). I would prefer not to pass the data (a savegame stored as a file, small in size < 20k) as a file (ie. overriding openFile()) since this would necessitate some complicated temp-file scheme to cope with concurrency with several content provider accesses and a running game. I would like to read the file into memory under a mutex lock and then pass the binary array in the simplest way possible. How do I do this? It seems creating a file in memory is not a possibility due to the return type of openFile(). query() needs to return a Cursor. Using MatrixCursor is not possible since it applies toString() to all stored objects when reading it. What do I need to do? Implement a custom Cursor? This class has 30 abstract methods. Do I read the file, put it in a SQLite db and return the cursor? The complexity of this seemingly simple task is mindboggling.

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• Using Excel as front end to Access database (with VBA)

  - by Alex

  I am building a small application for a friend and they'd like to be able to use Excel as the front end. (the UI will basically be userforms in Excel). They have a bunch of data in Excel that they would like to be able to query but I do not want to use excel as a database as I don't think it is fit for that purpose and am considering using Access. [BTW, I know Access has its shortcomings but there is zero budget available and Access already on friend's PC] To summarise, I am considering dumping a bunch of data into Access and then using Excel as a front end to query the database and display results in a userform style environment. Questions: How easy is it to link to Access from Excel using ADO / DAO? Is it quite limited in terms of functionality or can I get creative? Do I pay a performance penalty (vs.using forms in Access as the UI)? Assuming that the database will always be updated using ADO / DAO commands from within Excel VBA, does that mean I can have multiple Excel users using that one single Access database and not run into any concurrency issues etc.? Any other things I should be aware of? I have strong Excel VBA skills and think I can overcome Access VBA quite quickly but never really done Excel / Access link before. I could shoehorn the data into Excel and use as a quasi-database but that just seems more pain than it is worth (and not a robust long term solution) Any advice appreciated. Alex

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• WCF Callback Contract InvalidOperationException: Collection has been modified

  - by mrlane

  We are using a WCF service with a Callback contract. Communication is Asynchronous. The service contract is defined as: [ServiceContract(Namespace = "Silverlight", CallbackContract = typeof(ISessionClient),SessionMode = SessionMode.Allowed)] public interface ISessionService With a method: [OperationContract(IsOneWay = true)] void Send(Message message); The callback contract is defined as [ServiceContract] public interface ISessionClient With methods: [OperationContract(IsOneWay = true, AsyncPattern = true)] IAsyncResult BeginSend(Message message, AsyncCallback callback, object state); void EndSend(IAsyncResult result); The implementation of BeginSend and EndSend in the callback channel are as follows: public void Send(ActionMessage actionMessage) { Message message = Message.CreateMessage(_messageVersion, CommsSettings.SOAPActionReceive, actionMessage, _messageSerializer); lock (LO_backChannel) { try { _backChannel.BeginSend(message, OnSendComplete, null); } catch (Exception ex) { _hasFaulted = true; } } } private void OnSendComplete(IAsyncResult asyncResult) { lock (LO_backChannel) { try { _backChannel.EndSend(asyncResult); } catch (Exception ex) { _hasFaulted = true; } } } We are getting an InvalidOperationException: "Collection has been modified" on _backChannel.EndSend(asyncResult) seemingly randomly, and we are really out of ideas about what is causing this. I understand what the exception means, and that concurrency issues are a common cause of such exceptions (hence the locks), but it really doesn't make any sense to me in this situation. The clients of our service are Silverlight 3.0 clients using PollingDuplexHttpBinding which is the only binding available for Silverlight. We have been running fine for ages, but recently have been doing a lot of data binding, and this is when the issues started. Any help with this is appreciated as I am personally stumped at this time.

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