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  • Java - JPA - When we need more than one EntityManager?

    - by Yatendra Goel
    I am learning JPA and have one question: In which situations we need more than one EntityManager in our application? The two situations that I am aware of are as follows: When our application is a multi-threaded application and more than one thread needs JPA transaction because EntityManager is not thread-safe and we need one EntityManager per thread. When any of the thread needs multiple concurrent transactions, we need more than one EntityManager in that thread because there is one-to-one relationship between EntityManager and EntityTransaction. Q1. Are there any other situations when we need more than one EntityManager? ================================================================================= Q2. Upto my understanding, there should be only one EntityManagerFactory per Persitence Unit. Am I correct? If not, then what are those situations when we need multiple EntityManagerFactory per Persistence Unit?

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  • Preoder traversal of a Btree

    - by Phenom
    I'm trying to figure out how to do a preorder traversal of a Btree. I know that generally preorder traversal works like this: preorder(node) { print value in node preorder(left child) preorder(right child) } What's confusing to me is how to make this work with a Btree, since in each node there are multiple values and multiple child pointers. When printing values, do all the values in the node get printed before descending into the left child? Each node looks like this: child1 value1 child2 value2 child3 value3 child4 Also, why would anyone want to do a preorder traversal of a Btree, since an inorder traversal is what will display the values in ascending order?

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  • How to disable multitouch?

    - by cannyboy
    My app has several buttons which trigger different events. The user should NOT be able to hold down several buttons. Anyhow, holding down several buttons crashes the app. And so, I'm trying to disable multi-touch in my app. I've unchecked 'Multiple Touch' in all the xib files, and as far as I can work out, the properties 'multipleTouchEnabled' and 'exclusiveTouch' control whether the view uses multitouch. So in my applicationDidFinishLaunching I've put this: self.mainViewController.view.multipleTouchEnabled=NO; self.mainViewController.view.exclusiveTouch =YES; And in each of my view controllers I've put this in the viewDidLoad self.view.multipleTouchEnabled=NO; self.view.exclusiveTouch=YES; However, it still accepts multiple touches. I could do something like disable other buttons after getting a touch down event, but this would be an ugly hack. Surely there is a way to properly disable multi-touch?

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  • SQL Server Process Queue Race Condition

    - by William Edmondson
    I have an order queue that is accessed by multiple order processors through a stored procedure. Each processor passes in a unique ID which is used to lock the next 20 orders for its own use. The stored procedure then returns these records to the order processor to be acted upon. There are cases where multiple processors are able to retrieve the same 'OrderTable' record at which point they try to simultaneously operate on it. This ultimately results in errors being thrown later in the process. My next course of action is to allow each processor grab all available orders and just round robin the processors but I was hoping to simply make this section of code thread safe and allow the processors to grab records whenever they like. So Explicitly - Any idea why I am experiencing this race condition and how I can solve the problem. BEGIN TRAN UPDATE OrderTable WITH ( ROWLOCK ) SET ProcessorID = @PROCID WHERE OrderID IN ( SELECT TOP ( 20 ) OrderID FROM OrderTable WITH ( ROWLOCK ) WHERE ProcessorID = 0) COMMIT TRAN SELECT OrderID, ProcessorID, etc... FROM OrderTable WHERE ProcessorID = @PROCID

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  • How to use IObservable/IObserver with ConcurrentQueue or ConcurrentStack

    - by James Black
    I realized that when I am trying to process items in a concurrent queue using multiple threads while multiple threads can be putting items into it, the ideal solution would be to use the Reactive Extensions with the Concurrent data structures. My original question is at: http://stackoverflow.com/questions/2997797/while-using-concurrentqueue-trying-to-dequeue-while-looping-through-in-parallel/ So I am curious if there is any way to have a LINQ (or PLINQ) query that will continuously be dequeueing as items are put into it. I am trying to get this to work in a way where I can have n number of producers pushing into the queue and a limited number of threads to process, so I don't overload the database. If I could use Rx framework then I expect that I could just start it, and if 100 items are placed in within 100ms, then the 20 threads that are part of the PLINQ query would just process through the queue. There are three technologies I am trying to work together: Rx Framework (Reactive LINQ) PLING System.Collections.Concurrent structures

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  • Best Fit Scheduling Algorithim

    - by Teegijee
    I'm writing a scheduling program with a difficult programming problem. There are several events, each with multiple meeting times. I need to find an arrangement of meeting times such that each schedule contains any given event exactly once, using one of each event's multiple meeting times. Obviously I could use brute force, but that's rarely the best solution. I'm guessing this is a relatively basic computer science problem, which I'll learn about once I am able to start taking computer science classes. In the meantime, I'd prefer any links where I could read up on this, or even just a name I could Google.

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  • ObjectContext ConnectionString Sqlite

    - by codegarten
    I need to connect to a database in Sqlite so i downloaded and installed System.Data.SQLite and with the designer dragged all my tables. The designer created a .cs file with public class Entities : ObjectContext and 3 constructors: 1st public Entities() : base("name=Entities", "Entities") this one load the connection string from App.config and works fine. App.config <connectionStrings> <add name="Entities" connectionString="metadata=res://*/Db.TracModel.csdl|res://*/Db.TracModel.ssdl|res://*/Db.TracModel.msl;provider=System.Data.SQLite;provider connection string=&quot;data source=C:\Users\Filipe\Desktop\trac.db&quot;" providerName="System.Data.EntityClient" /> </connectionStrings> 2nd public Entities(string connectionString) : base(connectionString, "Entities") 3rd public Entities(EntityConnection connection) : base(connection, "Entities") Here is the problem, i already tried n configuration, already used EntityConnectionStringBuilder to make the connection string with no luck. Can you please point me in the right direction!? EDIT(1) How can i construct a valid connection string?!

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  • spring add default value to form:select

    - by Mike
    I'm developing a spring application, now I've added a dropdownlist to one of my jsp pages using: <form:select multiple="single" path="users[y.count-1].X" items="${Y}" itemValue="id" itemLabel="name"/> Now I'd like to add the default value "Nothing selected", however I can't seem to find how to do this. I've tried: <form:select multiple="single" path="users[y.count-1].X" items="${Y}" itemValue="id" itemLabel="name"> <form:option value="Nothing selected" /> </form:select> But "Nothing selected" isn't displayed in my dropdownlist.

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  • asp.net search application index update help

    - by srinivasan
    hi im developing a simple search application( ASP.Net VB.Net) the index table is actually a hash table ll be stored in my file system. the search page ll open this in read mode n copy this to a hash table object n perform search. other update n delete functions will open this in write mode n update it. what should i ve to do to make this app correct that there shud not be any execption when multiple user accessing these things at the same time. wat do i ve to do to make this robust and error free. i want multiple users to access search page without any problem n the index updation also in a parallel manner thanks srinivasan

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  • jQuery autocomplete function, how to add support for words not available in the database yet?

    - by Lyon
    Hi, I'm looking to implement a tag system like how SO uses on their site, where users can specify multiple tag words. However, on top of all the other autocomplete functions available as jquery plugins, I also want to allow users to enter new words not in the database. Does anyone know of any plugin that can do that? Or if there isn't, how one can add that functionality to an existing autocomplete function? I'm exploring Drew Wilson's autosuggest plugin at the moment, as it supports multiple tags well: http://code.drewwilson.com/entry/autosuggest-jquery-plugin Any help appreciated! Thanks :)

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  • Bloomberg APIv3 returning Slow Consumer Warnings!

    - by Marcus
    I made a program in c# based on the example "SubscriptionWithEventHandlerExample" of API 3.2.9.0. After subscribing to about 500 securities for realtime data, I receive some ADMIN event warnings claiming SlowConsumerWarning and SlowConsumerWarningCleared. I read somewhere that it introduces some delay, until I process all events. The problem is that in my code I only receive callbacks from bloomberg. The event queue isn´t even in my program! Some things that I tried: 1) raise the queue limit, setting MaxEventQueueSize in the session options (seems to have no effect) 2) see if I get any timeout event (no, I don't get any) 3) create multiple sessions and subscribing 50 securities in each (now I get multiple warnings, one for each thread) Is there something that I can do or this behavior is out of my scope?

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  • How to simulate a file read error in the CRT

    - by Mark0978
    Using VS2008, we would like to simulate a file that has a size of X, but that has a read failure at X-Y bytes, so that we get an error indication. Anyone have an idea of how to do this on windows? Looks like there is a solution for linux, but I can't really come up with a way to do this on windows. We have multiple developers, multiple machines, and cppunit testing framework, so I want a software only design. I'm trying to simulate the actual CRT failing, so I can test the code that is dealing with the failure.

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  • Is there an equivalent in Scala to Python's more general map function?

    - by wheaties
    I know that Scala's Lists have a map implementation with signature (f: (A) => B):List[B] and a foreach implementation with signature (f: (A) => Unit):Unit but I'm looking for something that accepts multiple iterables the same way that the Python map accepts multiple iterables. I'm looking for something with a signature of (f: (A,B) => C, Iterable[A], Iterable[B] ):Iterable[C] or equivalent. Is there a library where this exists or a comparable way of doing similar?

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  • Interface Design Problem: Storing Result of Transactions

    - by jboyd
    Requirements: multiple sources of input (social media content) into a system multiple destinations of output (social media api's) sources and destinations WILL be added some pseudo: IContentProvider contentProvider = context.getBean("contentProvider"); List<Content> toPost = contentProvider.getContent(); for (Content c : toPost) { SocialMediaPresence smPresence = socialMediaService.getSMPresenceBySomeId(c.getDestId()); smPresence.hasTwitter(); smPresence.hasFacebook(); //just to show what this is smPresence.postContent(c); //post content could fail for some SM platforms, but shoulnd't be lost forever } So now I run out of steam, I need to know what content has been successfully posted, and if it hasn't gone too all platforms, or if another platform were added in the future that content needs to go out for it as well (therefore my content provider will need to not only know if content has gone out, but for what platforms). I'm not looking for code, although sample/pseudo is fine... I'm looking for an approach to this problem that I can implement

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  • Practical differences between classes and structs in .net (not conceptual)?

    - by Gulshan
    Whenever I tried to search about differences between classes and structs in C# or .net, I ended up with the conceptual overview of the two things like value type or the reference type, where the variables are allocated etc. But I need some practical differences. I have found some like different behavior of assignment operator, having constructors etc. Can anybody provide some more practical differences which will be directly useful while coding? Like the things works with one but not with other or same operation showing different behavior. And some common mistakes regarding these two. Also please suggest where to consider using a struct instead of a class. And where the structs should not be used.

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  • Initialization of std::vector<unsigned int> with a list of consecutive unsigned integers

    - by Thomas
    I want to use a special method to initialize a std::vector<unsigned int> which is described in a C++ book I use as a reference (the German book 'Der C++ Programmer' by Ulrich Breymann, in case that matters). In that book is a section on sequence types of the STL, referring in particular to list, vector and deque. In this section he writes that there are two special constructors of such sequence types, namely, if Xrefers to such a type, X(n, t) // creates a sequence with n copies of t X(i, j) // creates a sequence from the elements of the interval [i, j) I want to use the second one for an interval of unsigned int, that is std::vector<unsigned int> l(1U, 10U); to get a list initialized with {1,2,...,9}. What I get, however, is a vector with one unsigned int with value 10 :-| Does the second variant exist, and if yes, how do I force that it is called?

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  • I need an algorithm to find the best path

    - by user242635
    I need an algorithm to find the best solution of a path finding problem. The problem can be stated as: At the starting point I can proceed along multiple different paths. At each step there are another multiple possible choices where to proceed. There are two operations possible at each step: A boundary condition that determine if a path is acceptable or not. A condition that determine if the path has reached the final destination and can be selected as the best one. At each step a number of paths can be eliminated, letting only the "good" paths to grow. I hope this sufficiently describes my problem, and also a possible brute force solution. My question is: is the brute force is the best/only solution to the problem, and I need some hint also about the best coding structure of the algorithm.

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  • Fast single thread comet server, possible?

    - by Pepijn
    I recently encountered a few cases where a server would distribute an event stream that contains the exact same data for all listeners, such as a 'recent activity' box. It occurred to me that it is quite strange and inefficient to have a server like Apache run a thread processing and querying the database for every single comet stream containing the same data. What I would do for those global(not per user) streams is run a single thread that continuously emits data, and a new (green)thread for every new request that outputs the headers and then 'merges' into the main thread. Is it possible for one thread to serve multiple sockets, or for multiple clients to listen to the same socket? An example o = event # threads received | a b # 3 o / / # 3 - |/_/ | # 1 o c # 2 a, b | / o/ # 2 a, b o # 1 a, b, c | # connection b closed o # 1 a, c Does something like this exist? Would it work? Is it possible to do? Disclaimer: I'm not a server expert.

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  • How to make Spring accept fluent (non-void) setters?

    - by Chris
    Hi, I have an API which I am turning into an internal DSL. As such, most methods in my PoJos return a reference to this so that I can chain methods together declaratively as such (syntactic sugar). myComponent .setID("MyId") .setProperty("One") .setProperty2("Two") .setAssociation(anotherComponent) .execute(); My API does not depend on Spring but I wish to make it 'Spring-Friendly' by being PoJo friendly with zero argument constructors, getters and setters. The problem is that Spring seems to not detect my setter methods when I have a non-void return type. The return type of this is very convenient when chaining together my commands so I don't want to destroy my programmatic API just be to compatible with Spring injection. Is there a setting in Spring to allow me to use non-void setters? Chris

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  • Reading option values in select

    - by user281180
    I have select values as follows: <select id="SelectBox" multiple="multiple"> <% foreach (var item in Model.Name) { %> <option value="<%= item.Value %>"><%=item.Text%></option> <% } %> </select> I have a function in jquery that will have to read both the text and value. I need to have the values in array so that I can display them in a table with a column Id and another column text. My problem is that Im not able to retrieve each and every value separately. Im having the text in one line, test1test2test3. function read() { $("#SelectBox").each(function() { var value = $(this).val(); var text = $(this).text(); alert(value);alert(text); }); }

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  • Persistence provider for Java that supports final fields

    - by naeron84
    I'm very new to Java but I've been developing a habit to use final wherever possible declaring immutability which i think is a good thing. (Consider f#) I've read that JPA does not support final fields. Hibernate, TopLink? I'm not sure about these but i prefer JPA for now. Is that even possible theoretically - let's say through reflection - to modify final fields after creation? My guess would be... NO :) What would be certainly possible for a persistence solution is to support constructors with parameters. At least i see no reason that would make this impossible. Mapping would be a little tricky i guess. This is an alternative solution. Suggestions?

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