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  • delta-dictionary/dictionary with revision awareness in python?

    - by shabbychef
    I am looking to create a dictionary with 'roll-back' capabilities in python. The dictionary would start with a revision number of 0, and the revision would be bumped up only by explicit method call. I do not need to delete keys, only add and update key,value pairs, and then roll back. I will never need to 'roll forward', that is, when rolling the dictionary back, all the newer revisions can be discarded, and I can start re-reving up again. thus I want behaviour like: >>> rr = rev_dictionary() >>> rr.rev 0 >>> rr["a"] = 17 >>> rr[('b',23)] = 'foo' >>> rr["a"] 17 >>> rr.rev 0 >>> rr.roll_rev() >>> rr.rev 1 >>> rr["a"] 17 >>> rr["a"] = 0 >>> rr["a"] 0 >>> rr[('b',23)] 'foo' >>> rr.roll_to(0) >>> rr.rev 0 >>> rr["a"] 17 >>> rr.roll_to(1) Exception ... Just to be clear, the state associated with a revision is the state of the dictionary just prior to the roll_rev() method call. thus if I can alter the value associated with a key several times 'within' a revision, and only have the last one remembered. I would like a fairly memory-efficient implementation of this: the memory usage should be proportional to the deltas. Thus simply having a list of copies of the dictionary will not scale for my problem. One should assume the keys are in the tens of thousands, and the revisions are in the hundreds of thousands. We can assume the values are immutable, but need not be numeric. For the case where the values are e.g. integers, there is a fairly straightforward implementation (have a list of dictionaries of the numerical delta from revision to revision). I am not sure how to turn this into the general form. Maybe bootstrap the integer version and add on an array of values? all help appreciated.

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  • stoping doGet/dopost in java servlets ?

    - by bosso
    Hello everyone, I've been playing with Java Servlets and Ajax a bit, and I've got a situation on which I would really appreciate advice. Let's say I have HTML page with a start and stop buttons, and as a result of clicking start button, overridden doGet (or doPost) method on a servlet is invoked which computes something that takes a long time to complete. (e.g. a giant loop, or even Infinite loop, doesn't matter, I'm interested in concepts here). So, I'm asking you: 1.What would be my options to kill / shut down / halt / exit doGet method whan I hit stop button on a web page? Do I use threading here, or there is simpler way? I take it that using System exit is not a very good idea, right? ;) 2.So, let's say I implement code for stopping doGet method. What would happen If I hit start on one browser(e.g.IE), and while this long computation takes place open new tab or other browser(e.g.Firefox) and open same url and hit stop? Would that stop my original computation? Is there any easy way to avoid this? I know that questions are a bit off, as I'm just starting with server-side of things. :) Any suggestions would be greatly appreciated!

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  • Oracle performance problem

    - by jreid42
    We are using an Oracle 11G machine that is very powerful; has redundant storage etc. It's a beast from what I have been told. We just got this DB for a tool that when I first came on as a coop had like 20 people using, now its upwards of 150 people. I am the only one working on it :( We currently have a system in place that distributes PERL scripts across our entire data center essentially giving us a sort of "grid" computing power. The Perl scripts run a sort of simulation and report back the results to the database. They do selects / inserts. The load is not very high for each script but it could be happening across 20-50 systems at the same time. We then have multiple data centers and users all hitting the same database with this same approach. Our main problem with this is that our database is getting overloaded with connections and having to drop some. We sometimes have upwards of 500 connections. These are old perl scripts and they do not handle this well. Essentially they fail and the results are lost. I would rather avoid having to rewrite a lot of these as they are poorly written, and are a headache to even look at. The database itself is not overloaded, just the connection overhead is too high. We open a connection, make a quick query and then drop the connection. Very short connections but many of them. The database team has basically said we need to lower the number of connections or they are going to ignore us. Because this is distributed across our farm we cant implement persistent connections. I do this with our webserver; but its on a fixed system. The other ones are perl scripts that get opened and closed by the distribution tool and thus arent always running. What would be my best approach to resolving this issue? The scripts themselves can wait for a connection to be open. They do not need to act immediately. Some sort of queing system? I've been suggested to set up a few instances of a tool called "SQL Relay". Maybe one in each data center. How reliable is this tool? How good is this approach? Would it work for what we need? We could have one for each data center and relay requests through it to our main database, keeping a pipeline of open persistent connections? Does this make sense? Is there any other suggestions you can make? Any ideas? Any help would be greatly appreciated. Sadly I am just a coop student working for a very big company and somehow all of this has landed all on my shoulders (there is literally nobody to ask for help; its a hardware company, everybody is hardware engineers, and the database team is useless and in India) and I am quite lost as what the best approach would be? I am extremely overworked and this problem is interfering with on going progress and basically needs to be resolved as quickly as possible; preferably without rewriting the whole system, purchasing hardware (not gonna happen), or shooting myself in the foot. HELP LOL!

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  • With a jquery modular dialog how do I stop the form values from persisting?

    - by stormist
    (Citing source at: http://jqueryui.com/demos/dialog/#modal-form) As an example, this works great but each time the form is subsequently opened the user entered values remain. How can I stop this behavior? (the form will be used multiple times on the same page. <style type="text/css"> body { font-size: 62.5%; } label, input { display:block; } input.text { margin-bottom:12px; width:95%; padding: .4em; } fieldset { padding:0; border:0; margin-top:25px; } h1 { font-size: 1.2em; margin: .6em 0; } div#users-contain { width: 350px; margin: 20px 0; } div#users-contain table { margin: 1em 0; border-collapse: collapse; width: 100%; } div#users-contain table td, div#users-contain table th { border: 1px solid #eee; padding: .6em 10px; text-align: left; } .ui-dialog .ui-state-error { padding: .3em; } .validateTips { border: 1px solid transparent; padding: 0.3em; } </style> <script type="text/javascript"> $(function() { // a workaround for a flaw in the demo system (http://dev.jqueryui.com/ticket/4375), ignore! $("#dialog").dialog("destroy"); var name = $("#name"), email = $("#email"), password = $("#password"), allFields = $([]).add(name).add(email).add(password), tips = $(".validateTips"); function updateTips(t) { tips .text(t) .addClass('ui-state-highlight'); setTimeout(function() { tips.removeClass('ui-state-highlight', 1500); }, 500); } function checkLength(o,n,min,max) { if ( o.val().length > max || o.val().length < min ) { o.addClass('ui-state-error'); updateTips("Length of " + n + " must be between "+min+" and "+max+"."); return false; } else { return true; } } function checkRegexp(o,regexp,n) { if ( !( regexp.test( o.val() ) ) ) { o.addClass('ui-state-error'); updateTips(n); return false; } else { return true; } } $("#dialog-form").dialog({ autoOpen: false, height: 300, width: 350, modal: true, buttons: { 'Create an account': function() { var bValid = true; allFields.removeClass('ui-state-error'); bValid = bValid && checkLength(name,"username",3,16); bValid = bValid && checkLength(email,"email",6,80); bValid = bValid && checkLength(password,"password",5,16); bValid = bValid && checkRegexp(name,/^[a-z]([0-9a-z_])+$/i,"Username may consist of a-z, 0-9, underscores, begin with a letter."); // From jquery.validate.js (by joern), contributed by Scott Gonzalez: http://projects.scottsplayground.com/email_address_validation/ bValid = bValid && checkRegexp(email,/^((([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+(\.([a-z]|\d|[!#\$%&'\*\+\-\/=\?\^_`{\|}~]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])+)*)|((\x22)((((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(([\x01-\x08\x0b\x0c\x0e-\x1f\x7f]|\x21|[\x23-\x5b]|[\x5d-\x7e]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(\\([\x01-\x09\x0b\x0c\x0d-\x7f]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]))))*(((\x20|\x09)*(\x0d\x0a))?(\x20|\x09)+)?(\x22)))@((([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|\d|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.)+(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])|(([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])([a-z]|\d|-|\.|_|~|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])*([a-z]|[\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])))\.?$/i,"eg. [email protected]"); bValid = bValid && checkRegexp(password,/^([0-9a-zA-Z])+$/,"Password field only allow : a-z 0-9"); if (bValid) { $('#users tbody').append('<tr>' + '<td>' + name.val() + '</td>' + '<td>' + email.val() + '</td>' + '<td>' + password.val() + '</td>' + '</tr>'); $(this).dialog('close'); } }, Cancel: function() { $(this).dialog('close'); } }, close: function() { allFields.val('').removeClass('ui-state-error'); } }); $('#create-user') .button() .click(function() { $('#dialog-form').dialog('open'); }); }); </script> <div class="demo"> <div id="dialog-form" title="Create new user"> <p class="validateTips">All form fields are required.</p> <form> <fieldset> <label for="name">Name</label> <input type="text" name="name" id="name" class="text ui-widget-content ui-corner-all" /> <label for="email">Email</label> <input type="text" name="email" id="email" value="" class="text ui-widget-content ui-corner-all" /> <label for="password">Password</label> <input type="password" name="password" id="password" value="" class="text ui-widget-content ui-corner-all" /> </fieldset> </form> </div> <div id="users-contain" class="ui-widget"> <h1>Existing Users:</h1> <table id="users" class="ui-widget ui-widget-content"> <thead> <tr class="ui-widget-header "> <th>Name</th> <th>Email</th> <th>Password</th> </tr> </thead> <tbody> <tr> <td>John Doe</td> <td>[email protected]</td> <td>johndoe1</td> </tr> </tbody> </table> </div> <button id="create-user">Create new user</button> </div><!-- End demo --> <div class="demo-description"> <p>Use a modal dialog to require that the user enter data during a multi-step process. Embed form markup in the content area, set the <code>modal</code> option to true, and specify primary and secondary user actions with the <code>buttons</code> option.</p> </div><!-- End demo-description -->

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  • JPA merge fails due to duplicate key

    - by wobblycogs
    I have a simple entity, Code, that I need to persist to a MySQL database. public class Code implements Serializable { @Id private String key; private String description; ...getters and setters... } The user supplies a file full of key, description pairs which I read, convert to Code objects and then insert in a single transaction using em.merge(code). The file will generally have duplicate entries which I deal with by first adding them to a map keyed on the key field as I read them in. A problem arises though when keys differ only by case (for example: XYZ and XyZ). My map will, of course, contain both entries but during the merge process MySQL sees the two keys as being the same and the call to merge fails with a MySQLIntegrityConstraintViolationException. I could easily fix this by uppercasing the keys as I read them in but I'd like to understand exactly what is going wrong. The conclusion I have come to is that JPA considers XYZ and XyZ to be different keys but MySQL considers them to be the same. As such when JPA checks its list of known keys (or does whatever it does to determine whether it needs to perform an insert or update) it fails to find the previous insert and issuing another which then fails. Is this corrent? Is there anyway round this other than better filtering the client data? I haven't defined .equals or .hashCode on the Code class so perhaps this is the problem.

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  • Unit Testing & Fake Repository implementation with cascading CRUD operations

    - by Erik Ashepa
    Hi, i'm having trouble writing integration tests which use a fake repository, For example : Suppose I have a classroom entity, which aggregates students... var classroom = new Classroom(); classroom.Students.Add(new Student("Adam")); _fakeRepository.Save(classroom); _fakeRepostiory.GetAll<Student>().Where((student) => student.Name == "Adam")); // This query will return null... When using my real implementation for repository (NHibernate based), the above code works (because the save operation would cascade to the student added at the previous line), Do you know of any fake repository implementation which support this behaviour? Ideas on how to implement one myself? Or do you have any other suggestions which could help me avoid this issue? Thanks in advance, Erik.

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  • WF performance with new 20,000 persisted workflow instances each month

    - by Nikola Stjelja
    Windows Workflow Foundation has a problem that is slow when doing WF instances persistace. I'm planning to do a project whose bussiness layer will be based on WF exposed WCF services. The project will have 20,000 new workflow instances created each month, each instance could take up to 2 months to finish. What I was lead to belive that given WF slownes when doing peristance my given problem would be unattainable given performance reasons. I have the following questions: Is this true? Will my performance be crap with that load(given WF persitance speed limitations) How can I solve the problem? We currently have two possible solutions: 1. Each new buisiness process request(e.g. Give me a new drivers license) will be a new WF instance, and the number of persistance operations will be limited by forwarding all status request operations to saved state values in a separate database. 2. Have only a small amount of Workflow Instances up at any give time, without any persistance ofso ever(only in case of system crashes etc.), by breaking each workflow stap in to a separate worklof and that workflow handling each business process request instance in the system that is at that current step(e.g. I'm submitting my driver license reques form, which is step one... we have 100 cases of that, and my step one workflow will handle every case simultaneusly). I'm very insterested in solution for that problem. If you want to discuss that problem pleas be free to mail me at [email protected]

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  • Google App Engine ClassNotPersistenceCapableException

    - by Frank
    I have the following class : import javax.jdo.annotations.IdGeneratorStrategy; import javax.jdo.annotations.IdentityType; import javax.jdo.annotations.PersistenceCapable; import javax.jdo.annotations.Persistent; import javax.jdo.annotations.PrimaryKey; import com.google.appengine.api.datastore.*; @PersistenceCapable(identityType=IdentityType.APPLICATION) public class PayPal_Message { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Long id; @Persistent private Text content; @Persistent private String time; public PayPal_Message(Text content,String time) { this.content=content; this.time=time; } public Long getId() { return id; } public Text getContent() { return content; } public String getTime() { return time; } public void setContent(Text content) { this.content=content; } public void setTime(String time) { this.time=time; } } It used to be in a package, and works fine, now I put all classes in the default package, which caused me this error : org.datanucleus.jdo.exceptions.ClassNotPersistenceCapableException: The class "The class "PayPal_Message" is not persistable. This means that it either hasnt been enhanced, or that the enhanced version of the file is not in the CLASSPATH (or is hidden by an unenhanced version), or the Meta-Data/annotations for the class are not found." is not persistable. This means that it either hasnt been enhanced, or that the enhanced version of the file is not in the CLASSPATH (or is hidden by an unenhanced version), or the Meta-Data for the class is not found. NestedThrowables: org.datanucleus.exceptions.ClassNotPersistableException: The class "PayPal_Message" is not persistable. This means that it either hasnt been enhanced, or that the enhanced version of the file is not in the CLASSPATH (or is hidden by an unenhanced version), or the Meta-Data/annotations for the class are not found. What should I do to fix it ?

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  • How to install and use db4o for Android?

    - by Viet
    I have to admit that I'm new to Java and Android. db4o seems to be an excellent DB framework to replace SQLite http://developer.db4o.com/Platforms/Java/Android.aspx. I want to use it for my Android application. I don't know how to: Import/Install/Attach/Upload db4o to Android phone. Where should I put the JAR file db4o-7.12.132.14217-all-java5.jar so that it was uploaded to Android phone and it could be called from the application? Please kindly advise! Many thanks!!!

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  • ManyToMany Relation does not create the primary key

    - by Javi
    Hello, I have a ManyToMany relationship between two classes: ClassA and ClassB, but when the table for this relationship (table called objectA_objectB) there is no primary key on it. In my ClassA I have the following: @ManyToMany(fetch=FetchType.LAZY) @OrderBy(value="name") @JoinTable(name="objectA_objectB", joinColumns= @JoinColumn(name="idObjectA", referencedColumnName="id"), inverseJoinColumns= @JoinColumn(name="idObjectB", referencedColumnName="id") ) private List<ClassB> objectsB; and in my ClassB I have the reversed relation @ManyToMany List<ClassA> objectsA; I just want to make a primary key of both id's but I need to change the name of the columns as I do. Why is the PK missing? How can I define it? I use JPA 2.0 Hibernate implementation, if this helps. Thanks.

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  • Java Frameworks that support Entity-Attribute-Value Models

    - by jm04469
    I am interested in developing a portal-based application that works with EAV models and would like to know if there are any Java frameworks that aid in this type of development? salesforce.com uses EAV and currently has twenty tables. The framework I seek should allow it to be configurable to different EAV implementations

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  • Persist changes in C

    - by Mohit Deshpande
    I am developing a database-like application that stores a a structure containing: struct Dictionary { char *key; char *value; struct Dictionary *next; }; As you can see, I am using a linked list to store information. But the problem begins when the user exits out of the program. I want the information to be stored somewhere. So I was thinking of storing the linked list in a permanent or temporary file using fopen, then, when the user starts the program, retrieve the linked list. Here is the method that prints the linked list to the console: void PrintList() { int count = 0; struct Dictionary *current; current = head; if (current == NULL) { printf("\nThe list is empty!"); return; } printf(" Key \t Value\n"); printf(" ======== \t ========\n"); while (current != NULL) { count++; printf("%d. %s \t %s\n", count, current->key, current->value); current = current->next; } } So I am thinking of modifying this method to print the information through fprintf instead of printf and then the program would just get the infomation from the file. Could someone help me on how I can read and write to this file? What kind of file should it be, temporary or regular? How should I format the file (like I was thinking of just having the key first, then the value, then a newline character)?

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  • How to prevent "Local transaction already has 1 non-XA Resource" exception?

    - by Zeratul
    Hi, I'm using 2 PU in stateless EJB and each of them is invoked on one method: @PersistenceContext(unitName="PU") private EntityManager em; @PersistenceContext(unitName="PU2") private EntityManager em2; @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW ) public void getCandidates(final Integer eventId) throws ControllerException { ElectionEvent electionEvent = em.find(ElectionEvent.class, eventId); ... Person person = getPerson(candidate.getLogin()); ... } @TransactionAttribute(TransactionAttributeType.REQUIRES_NEW ) private Person getPerson(String login) throws ControllerException { Person person = em2.find(Person.class, login); return person; } Those methods are annotated with REQUIRES_NEW transcaction to avoid this exception. When I was calling these method from javaFX applet, all worked as expected. Now I'm trying to call them from JAX-RS webservice (I don't see any logical difference as in both cases ejb was looked up in initial context) and I keep getting this exception. When I set up XADatasource in glassfish 2.1 connection pools, I got nullpointer exception on em2. Any ideas what to try next? Regards

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  • Persisting a trie to a file - C

    - by Appu
    I have a trie which I am using to do some string processing. I have a simple compiler which generates trie from some data. Once generated, my trie won't change at run time. I am looking for an approach where I can persist the trie in a file and load it effectively. I have looked at sqllite to understand how they are persisting b-treebut their file format looks bit advanced and I may not need all of those. It'd be helpful if someone can provide some ideas to persist and read the trie. I am programming using C.

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  • One entityManger finds entity , the other does not.

    - by Pitelk
    Hi all, I have a very strange behavior in my program. I have 2 classes (class LogIn and CreateGame) where i have injected an EntityManager in each using the annotation @PersistenceContext(unitName="myUnitPU") EntityManager entitymanger; In some point i remove an object called "user" from the database using entitymanger.remove(user) from a method in LogIn class. The business logic is that a user can host and join games ( in the same time) so removing the user all the entries in database about the games the user has created are removed and all the entries showing in which games the user has joined are removed also. After that, i call another function which checks if the user exists using a method in the LogIn class entitymanager.find(user) which surprisingly enough, finds the user. After that I call a method in CreateGame class which tries to find the user by using again entitymanger.find(user) the entitymanger in that class fails to find the user (which is the expected result as the user is removed and it's not in the database) So the question is : Why the entitymanager in one class finds the user (which is wrong) where the other doesn't find it? Does anyone has ever the same problem? PS : This "bug" occurs when the user has hosted a game which is joined by another user (lets call him Buser) and the Buser has made a game which is joined by the current user. GAME | HOST | CLIENTS game1 | user | userB game2 | userB | user where in this case by removing the user, the game1 is deleted and the user is removed from game2 so the result is GAME | HOST | CLIENTS game2 | userB | PS2 : The Beans are EJB3.0. The methods are called from a delegate class. The beans in the delegate class are instantiated using the InitialContext.lookup() method. Note that for logging in ,creating , joining games the appropriate delegate class calls the correspondent EJB which does the transactions. In the case of logOut, the delegate calls an EJB to logout the user but becuase other stuff must be done (as said above) this EJB calls other EJB (again using lookup() ) which has methods like removegame(), removeUserFromGame() etc. After those methods are executed the user is then logged out. Maybe it has something to do with the fact the the first entity manager is called by a delegate but the second from inside an EJb and thats why the one entitymanger can see the non-existent user while the other cannot? Also all the methods have TRANSACTIONTYPE.REQUIRED Thank you in advance

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  • SPPersistedObject and List<T>

    - by Sam
    Hi I want sharepoint to "persist" a List of object I wrote a class SPAlert wich inherit from SPPersistedObject : public class SMSAlert: SPPersistedObject { [Persisted] private DateTime _scheduledTime; [Persisted] private Guid _listId; [Persisted] private Guid _siteID; } Then I wrote a class wich inherit from SPJobDefinition an add a List of my previous object: public sealed class MyCustomJob: SPJobDefinition { [Persisted] private List<SMSAlert> _SMSAlerts; } The problem is : when I call the Update method of y MyCustomJob: myCustomJob.Update(); It throw an exception : message : An object in the SharePoint administrative framework, depends on other objects which do not exist. Ensure that all of the objects dependencies are created and retry this operation. stack at Microsoft.SharePoint.Administration.SPConfigurationDatabase.StoreObject(SPPersistedObject obj, Boolean storeClassIfNecessary, Boolean ensure) at Microsoft.SharePoint.Administration.SPConfigurationDatabase.PutObject(SPPersistedObject obj, Boolean ensure) at Microsoft.SharePoint.Administration.SPPersistedObject.Update() at Microsoft.SharePoint.Administration.SPJobDefinition.Update() at Sigi.Common.AlertBySMS.SmsAlertHandler.ScheduleJob(SPWeb web, SPAlertHandlerParams ahp) inner exception An object in the SharePoint administrative framework depends on other objects which do not exist. The INSERT statement conflicted with the FOREIGN KEY constraint "FK_Dependencies1_Objects". The conflict occurred in database "SharePoint_Config, table "dbo.Objects", column 'Id'. The statement has been terminated. Can anyone help me with that??

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  • Passing empty list as parameter to JPA query throws error

    - by Tuukka Mustonen
    If I pass an empty list into a JPA query, I get an error. For example: List<Municipality> municipalities = myDao.findAll(); // returns empty list em.createQuery("SELECT p FROM Profile p JOIN p.municipality m WHERE m IN (:municipalities)") .setParameter("municipalities", municipalities) .getResultList(); Because the list is empty, Hibernate generates this in SQL as "IN ()", which gives me error with Hypersonic database. There is a ticket for this in Hibernate issue tracking but there are not many comments/activity there. I don't know about support in other ORM products or in JPA spec either. I don't like the idea of having to manually check for null objects and empty lists every time. Is there some commonly known approach/extension to this? How do you handle these situations?

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  • Storing simulation results in a persistent manner for Python?

    - by Az
    Background: I'm running multiple simuations on a set of data. For each session, I'm allocating projects to students. The difference between each session is that I'm randomising the order of the students such that all the students get a shot at being assigned a project they want. I was writing out some of the allocations in a spreadsheet (i.e. Excel) and it basically looked like this (tiny snapshot, actual table extends to a few thousand sessions, roughly 100 students). | | Session 1 | Session 2 | Session 3 | |----------|-----------|-----------|-----------| |Stu1 |Proj_AA |Proj_AB |Proj_AB | |----------|-----------|-----------|-----------| |Stu2 |Proj_AB |Proj_AA |Proj_AC | |----------|-----------|-----------|-----------| |Stu3 |Proj_AC |Proj_AC |Proj_AA | |----------|-----------|-----------|-----------| Now, the code that deals with the allocation currently stores a session in an object. The next time the allocation is run, the object is over-written. Thus what I'd really like to do is to store all the allocation results. This is important since I later need to derive from the data, information such as: which project Stu1 got assigned to the most or perhaps how popular Proj_AC was (how many times it was assigned / number of sessions). Question(s): What methods can I possibly use to basically store such session information persistently? Basically, each session output needs to add itself to the repository after ending and before beginning the next allocation cycle. One solution that was suggested by a friend was mapping these results to a relational database using SQLAlchemy. I kind of like the idea since this does give me an opportunity to delve into databases. Now the database structure I was recommended was: |----------|-----------|-----------| |Session |Student |Project | |----------|-----------|-----------| |1 |Stu1 |Proj_AA | |----------|-----------|-----------| |1 |Stu2 |Proj_AB | |----------|-----------|-----------| |1 |Stu3 |Proj_AC | |----------|-----------|-----------| |2 |Stu1 |Proj_AB | |----------|-----------|-----------| |2 |Stu2 |Proj_AA | |----------|-----------|-----------| |2 |Stu3 |Proj_AC | |----------|-----------|-----------| |3 |Stu1 |Proj_AB | |----------|-----------|-----------| |3 |Stu2 |Proj_AC | |----------|-----------|-----------| |3 |Stu3 |Proj_AA | |----------|-----------|-----------| Here, it was suggested that I make the Session and Student columns a composite key. That way I can access a specific record for a particular student for a particular session. Or I can merely get the entire allocation run for a particular session. Questions: Is the idea a good one? How does one implement and query a composite key using SQLAlchemy? What happens to the database if a particular student is not assigned a project (happens if all projects that he wants are taken)? In the code, if a student is not assigned a project, instead of a proj_id he simply gets None for that field/object. I apologise for asking multiple questions but since these are closely-related, I thought I'd ask them in the same space.

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  • Oracle thin driver vs. OCI driver. Pros and Cons?

    - by Zwei Steinen
    Hi, When you develop a Java application that talks to oracle DBs, there are 2 options right? One is oracle thin driver, and the other is OCI driver that requires its own installation (please correct if I'm misunderstanding). Now, what are the pros and cons? Obviously thin driver sounds much better in terms of installation, but is there anything that OCI can and the thin one can't? Develop environment is Tomcat6 + Spring 3.0 + JPA(Hibernate) + appache-DBCP Thanks in advance.

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  • JPA query for getting the whole tree

    - by Javi
    Hello, I have a class which models all categories and they can be ordered hierarchically. @Entity @Table(name="categories") public class Category { @Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="sequence") @SequenceGenerator(name="sequence", sequenceName="categories_pk_seq", allocationSize=1) @Column(name="id") private Long id; @Column private String name; @OneToOne @JoinColumn(name="idfather") private Category father; } I need to get all categories ordered hierarchically (I mean every father followed by its children and fathers ordered alphabetically on each level) as they could be made for example with PRIOR in oracle. Is it possible to do this with a JPA Query (not a SQL one)? Thanks.

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  • Explaining persistent data structures in simple terms

    - by Jason Baker
    I'm working on a library for Python that implements some persistent data structures (mainly as a learning exercise). However, I'm beginning to learn that explaining persistent data structures to people unfamiliar with them can be difficult. Can someone help me think of an easy (or at least the least complicated) way to describe persistent data structures to them? I've had a couple of people tell me that the documentation that I have is somewhat confusing. (And before anyone asks, no I don't mean persistent data structures as in persisted to the file system. Google persistent data structures if you're unclear on this.)

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  • JSF: how to update the list after delete an item of that list

    - by Harry Pham
    It will take a moment for me to explain this, so please stay with me. I have table COMMENT that has OneToMany relationship with itself. @Entity public class Comment(){ ... @ManyToOne(optional=true, fetch=FetchType.LAZY) @JoinColumn(name="REPLYTO_ID") private Comment replyTo; @OneToMany(mappedBy="replyTo", cascade=CascadeType.ALL) private List<Comment> replies = new ArrayList<Comment>(); public void addReply(NewsFeed reply){ replies.add(reply); reply.setReplyTo(this); } public void removeReply(NewsFeed reply){ replies.remove(reply); } } So you can think like this. Each comment can have a List of replies which are also type Comment. Now it is very easy for me to delete the original comment and get the updated list back. All I need to do after delete is this. allComments = myEJB.getAllComments(); //This will query the db and return updated list But I am having problem when trying to delete replies and getting the updated list back. So here is how I delete the replies. Inside my managed bean I have //Before invoke this method, I have the value of originalFeed, and deletedFeed set. //These original comments are display inside a p:dataTable X, and the replies are //displayed inside p:dataTable Y which is inside X. So when I click the delete button //I know which comment I want to delete, and if it is the replies, I will know //which one is its original post public void deleteFeed(){ if(this.deletedFeed != null){ scholarEJB.deleteFeeds(this.deletedFeed); if(this.originalFeed != null){ //Since the originalFeed is not null, this is the `replies` //that I want to delete scholarEJB.removeReply(this.originalFeed, this.deletedFeed); } feeds = scholarEJB.findAllFeed(); } } Then inside my EJB scholarEJB, I have public void removeReply(NewsFeed comment, NewsFeed reply){ comment = em.merge(comment); comment.removeReply(reply); em.persist(comment); } public void deleteFeeds(NewsFeed e){ e = em.find(NewsFeed.class, e.getId()); em.remove(e); } When I get out, the entity (the reply) get correctly removed from the database, but inside the feeds List, reference of that reply still there. It only until I log out and log back in that the reply disappear. Please help

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  • ActiveMQ - Removing queues programatically

    - by Eduardo Z.
    Fellow StackOverflowers, is there a way for me to remove a queue or a topic in ActiveMQ programatically? I am using ActiveMQ's standard persistency, and my application requires that, on startup, all new queues be dynamically re-created (unless there are messages stored in the queue, in which case, the queue should remain to exist). I am also creating all queues programatically through sessions. Is there an equivalent to that procedure, only to delete a queue? Querying and iterating through the existing queues would also be useful, but i haven't found a way to do that yet. Please help an ActiveMQ noob! =)

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  • MVC Paging and Sorting Patterns: How to Page or Sort Re-Using Form Criteria

    - by CRice
    What is the best ASP.NET MVC pattern for paging data when the data is filtered by form criteria? This question is similar to: http://stackoverflow.com/questions/1425000/preserve-data-in-net-mvc but surely there is a better answer? Currently, when I click the search button this action is called: [AcceptVerbs(HttpVerbs.Post)] public ActionResult Search(MemberSearchForm formSp, int? pageIndex, string sortExpression) {} That is perfect for the initial display of the results in the table. But I want to have page number links or sort expression links re-post the current form data (the user entered it the first time - persisted because it is returned as viewdata), along with extra route params 'pageIndex' or 'sortExpression', Can an ActionLink or RouteLink (which I would use for page numbers) post the form to the url they specify? <%= Html.RouteLink("page 2", "MemberSearch", new { pageIndex = 1 })%> At the moment they just do a basic redirect and do not post the form values so the search page loads fresh. In regular old web forms I used to persist the search params (MemberSearchForm) in the ViewState and have a GridView paging or sorting event reuse it.

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