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• unable to set fields of a collection-property elements after changing their order (elements becoming

  - by Jaroslav Záruba

  Hello I want to change order of objects in a collection, and then to access+modify fields of those items. Unfortunately the items somehow become 'deleted'. This is what I do... if(someCondition) { MainEvent mainEvent = pm.getObjectById(MainEvent.class, mainEventKey); /* * events in the original order * MainEvent.subEvents field is not in default fetch group, * therefore I also tried to add the named group into the * persistenceManeger fetch plan, no difference * (mainEvent is not instance of the Event sub/class BTW) */ List<Event> subEvents = mainEvent.getSubEvents(); // re-arrange the events according to keysOrdered { Map<Key, Event> eventMap = new HashMap<Key, Event>(); for(Event event : subEvents) eventMap.put(event.getKey(), event); List<Event> eventsOrdered = new LinkedList<Event>(); for(Key eventKey : keysOrdered) eventsOrdered.add(eventMap.put(eventKey, eventMap.get(eventKey))); // } // put the re-arranged items back into the collection property { subEvents.clear(); subEvents.addAll(eventsOrdered); // } pm.makePersistent(mainEvent); eventsOrdered = subEvents; } else eventsOrdered = getEventsUsingAlternateApproach(); /* * so by now the mainEvent variable does not exist; * could it be this lead the persistence manager to mark * my events as abandoned/obsolete/invalid/deleted...? */ for(Event event : eventsOrdered) event.setDate(new Date()); // -> "Cannot write fields to a deleted object" What am I doing wrong please?

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• JPA 2.0 Provider Hibernate

  - by Rooh

  I have very strange problem we are using jpa 2.0 with hibernate annotations based Database generated through JPA DDL is true and MySQL as Database; i will provide some reference classes and then my porblem. @MappedSuperclass public abstract class Common implements serializable{ @Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(name = "id", updatable = false) private Long id; @ManyToOne @JoinColumn private Address address; //with all getter and setters //as well equal and hashCode } @Entity public class Parent extends Common{ private String name; @OneToMany(cascade = {CascadeType.MERGE,CascadeType.PERSIST}, mappedBy = "parent") private List<Child> child; //setters and rest of class } @Entity public class Child extends Common{ //some properties with getter/setters } @Entity public class Address implements Serializable{ @Id @GeneratedValue(strategy = GenerationType.AUTO) @Column(name = "id", updatable = false) private Long id; private String street; //rest of class with get/setter } as in code you can see that parents and child classes extends Common class so both have address property and id , the problem occurs when change the address refference in parent class it reflect same change in all child objects in list and if change address refference in child class then on merge it will change address refference of parent as well i am not able to figure out is it is problem of jpa or hibernate

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• Assign sage variable values into R objects via sagetex and Sweave

  - by sheed03

  I am writing a short Sweave document that outputs into a Beamer presentation, in which I am using the sagetex package to solve an equation for two parameters in the beta binomial distribution, and I need to assign the parameter values into the R session so I can do additional processing on those values. The following code excerpt shows how I am interacting with sage: <<echo=false,results=hide>>= mean.raw <- c(5, 3.5, 2) theta <- 0.5 var.raw <- mean.raw + ((mean.raw^2)/theta) @ \begin{frame}[fragile] \frametitle{Test of Sage 2} \begin{sagesilent} var('a1, b1, a2, b2, a3, b3') eqn1 = [1000*a1/(a1+b1)==\Sexpr{mean.raw[1]}, ((1000*a1*b1)*(1000+a1+b1))/((a1+b1)^2*(a1+b1+1))==\Sexpr{var.raw[1]}] eqn2 = [1000*a2/(a2+b2)==\Sexpr{mean.raw[2]}, ((1000*a2*b2)*(1000+a2+b2))/((a2+b2)^2*(a2+b2+1))==\Sexpr{var.raw[2]}] eqn3 = [1000*a3/(a3+b3)==\Sexpr{mean.raw[3]}, ((1000*a3*b3)*(1000+a3+b3))/((a3+b3)^2*(a3+b3+1))==\Sexpr{var.raw[3]}] s1 = solve(eqn1, a1,b1) s2 = solve(eqn2, a2,b2) s3 = solve(eqn3, a3,b3) \end{sagesilent} Solutions of Beta Binomial Parameters: \begin{itemize} \item $\sage{s1[0]}$ \item $\sage{s2[0]}$ \item $\sage{s3[0]}$ \end{itemize} \end{frame} Everything compiles just fine, and in that slide I am able to see the solutions to the three equations respective parameters in that itemized list (for example the first item in the itemized list from that beamer slide is outputted as [a1=(328/667), b1=(65272/667)] (I am not able to post an image of the beamer slide but I hope you get the idea). I would like to save the parameter values a1,b1,a2,b2,a3,b3 into R objects so that I can use them in simulations. I cannot find any documentation in the sagetex package on how to save output from sage commands into variables for use with other programs (in this case R). Any suggestions on how to get these values into R?

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• systematizing error codes for a web app in php?

  - by user151841

  I'm working on a class-based php web app. I have some places where objects are interacting, and I have certain situations where I'm using error codes to communicate to the end user -- typically when form values are missing or invalid. These are situations where exceptions are unwarranted ( and I'm not sure I could avoid the situations with exceptions anyways). In one object, I have some 20 code numbers, each of which correspond to a user-facing message, and a admin/developer-facing message, so both parties know what's going on. Now that I've worked over the code several times, I find that it's difficult to quickly figure out what code numbers in the series I've already used, so I accidentally create conflicting code numbers. For instance, I just did that today with 12, 13, 14 and 15. How can I better organize this so I don't create conflicting error codes? Should I create one singleton class, errorCodes, that has a master list of all error codes for all classes, systematizing them across the whole web app? Or should each object have its own set of error codes, when appropriate, and I just keep a list in the commentary of the object, to use and update that as I go along?

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• Can't create new "enterprise" project in netbeans

  - by Danny

  I'm running netbeans 6.7.1 on Ubuntu Karmic. On the services tab I added a new glassfish v3 prelude server, I installed it to my home directory using the download button. I started the server and opened localhost:4848 to verify I can get into the admin panel. Then I did file-new projct and created a new java web-web application. On the configuration step of the wizard it preselected glassfish v3 prelude and java ee 5. I accepted and did a test run. I ran the project just fine. So now I did file-new projecct and attempted to create a Java EE-ejb module. When I arrive to the server configuration stage of the wizard, it doesn't show any servers on the server dropdown list (so it's empty), it also doesn't see any version of java on the "java ee version" dropdown list. This also happens for the other "Java EE" project types. I can't seem to get my head around why I can make a new web application but not an ejb module. Can anyone provide any insight to why it might not be seeing that I have java or glassfish installed when I try to make a new java ee project but I see it when I try to make a java web project?

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• How to properly translate the "var" result of a lambda expression to a concrete type?

  - by CrimsonX

  So I'm trying to learn more about lambda expressions. I read this question on stackoverflow, concurred with the chosen answer, and have attempted to implement the algorithm using a console app in C# using a simple LINQ expression. My question is: how do I translate the "var result" of the lambda expression into a usable object that I can then print the result? I would also appreciate an in-depth explanation of what is happening when I declare the outer => outer.Value.Frequency (I've read numerous explanations of lambda expressions but additional clarification would help) C# //Input : {5, 13, 6, 5, 13, 7, 8, 6, 5} //Output : {5, 5, 5, 13, 13, 6, 6, 7, 8} //The question is to arrange the numbers in the array in decreasing order of their frequency, preserving the order of their occurrence. //If there is a tie, like in this example between 13 and 6, then the number occurring first in the input array would come first in the output array. List<int> input = new List<int>(); input.Add(5); input.Add(13); input.Add(6); input.Add(5); input.Add(13); input.Add(7); input.Add(8); input.Add(6); input.Add(5); Dictionary<int, FrequencyAndValue> dictionary = new Dictionary<int, FrequencyAndValue>(); foreach (int number in input) { if (!dictionary.ContainsKey(number)) { dictionary.Add(number, new FrequencyAndValue(1, number) ); } else { dictionary[number].Frequency++; } } var result = dictionary.OrderByDescending(outer => outer.Value.Frequency); // How to translate the result into something I can print??

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• Common Lisp condition system for transfer of control

  - by Ken

  I'll admit right up front that the following is a pretty terrible description of what I want to do. Apologies in advance. Please ask questions to help me explain. :-) I've written ETLs in other languages that consist of individual operations that look something like: // in class CountOperation IEnumerable<Row> Execute(IEnumerable<Row> rows) { var count = 0; foreach (var row in rows) { row["record number"] = count++; yield return row; } } Then you string a number of these operations together, and call The Dispatcher, which is responsible for calling Operations and pushing data between them. I'm trying to do something similar in Common Lisp, and I want to use the same basic structure, i.e., each operation is defined like a normal function that inputs a list and outputs a list, but lazily. I can define-condition a condition (have-value) to use for yield-like behavior, and I can run it in a single loop, and it works great. I'm defining the operations the same way, looping through the inputs: (defun count-records (rows) (loop for count from 0 for row in rows do (signal 'have-value :value `(:count ,count @,row)))) The trouble is if I want to string together several operations, and run them. My first attempt at writing a dispatcher for these looks something like: (let ((next-op ...)) ;; pick an op from the set of all ops (loop (handler-bind ((have-value (...))) ;; records output from operation (setq next-op ...) ;; pick a new next-op (call next-op))) But restarts have only dynamic extent: each operation will have the same restart names. The restart isn't a Lisp object I can store, to store the state of a function: it's something you call by name (symbol) inside the handler block, not a continuation you can store for later use. Is it possible to do something like I want here? Or am I better off just making each operation function explicitly look at its input queue, and explicitly place values on the output queue?

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• How to create a generic C free function .

  - by nomemory

  I have some C structures related to a 'list' data structure. They look like this. struct nmlist_element_s { void *data; struct nmlist_element_s *next; }; typedef struct nmlist_element_s nmlist_element; struct nmlist_s { void (*destructor)(void *data); int (*cmp)(const void *e1, const void *e2); unsigned int size; nmlist_element *head; nmlist_element *tail; }; typedef struct nmlist_s nmlist; This way I can have different data types being hold in "nmlist_element-data" . The "constructor" (in terms of OOP) has the following signature: nmlist *nmlist_alloc(void (*destructor)(void *data)); Where "destructor" is specific function that de-allocated "data" (being hold by the nmlist_element). If I want to have a list containing integers as data, my "destructor" would like this: void int_destructor(void *data) { free((int*)data); } Still i find it rather "unfriendly" for me to write a destructor functions for every simple primitive data type. So is there a trick to write something like this ? (for primitives): void "x"_destructor(void *data, "x") { free(("x" *)data); } PS: I am not a macro fan myself, and in my short experience regarding C, i don't use them, unless necessary.

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• How can I assign a name to a task in TPL

  - by mehrandvd

  I'm going to use lots of tasks running on my application. Each bunch of tasks is running for some reason. I would like to name these tasks so when I watch the Parallel Tasks window, I could recognize them easily. With another point of view, consider I'm using tasks at the framework level to populate a list. A developer that use my framework is also using tasks for her job. If she looks at the Parallel Tasks Window she will find some tasks having no idea about. I want to name tasks so she can distinguish the framework tasks from her tasks. It would be very convenient if there was such API: var task = new Task(action, "Growth calculation task") or maybe: var task = Task.Factory.StartNew(action, "Populating the datagrid") or even while working with Parallel.ForEach Parallel.ForEach(list, action, "Salary Calculation Task" Is it possible to name a task? Is it possible to give ???Parallel.ForEach a naming structure (maybe using a lambda) so it creates tasks with that naming? Is there such API somewhere that I'm missing? I've also tried to use an inherited task to override it's ToString(). But unfortunately the Parallel Tasks window doesn't use ToString()! class NamedTask : Task { private string TaskName { get; set; } public NamedTask(Action action, string taskName):base(action) { TaskName = taskName; } public override string ToString() { return TaskName; } }

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• What's a reasonable way to mutate a primitive variable from an anonymous Java class?

  - by Steve

  I would like to write the following code: boolean found = false; search(new SearchCallback() { @Override void onFound(Object o) { found = true; } }); Obviously this is not allowed, since found needs to be final. I can't make found a member field for thread-safety reasons. What is the best alternative? One workaround is to define final class MutableReference<T> { private T value; MutableReference(T value) { this.value = value; } T get() { return value; } void set(T value) { this.value = value; } } but this ends up taking a lot of space when formatted properly, and I'd rather not reinvent the wheel if at all possible. I could use a List<Boolean> with a single element (either mutating that element, or else emptying the list) or even a Boolean[1]. But everything seems to smell funny, since none of the options are being used as they were intended. What is a reasonable way to do this?

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• How can I make keyword order more relevant in my search?

  - by Atomiton

  In my database, I have a keywords field that stores a comma-delimited list of keywords. For example, a Shrek doll might have the following keywords: ogre, green, plush, hero, boys' toys A "Beanie Baby" doll ( that happens to be an ogre ) might have: beanie baby, kids toys, beanbag toys, soft, infant, ogre (That's a completely contrived example.) What I'd like to do is if the consumer searches for "ogre" I'd like the "Shrek" doll to come up higher in the search results. My content administrator feels that if the keyword is earlier in the list, it should get a higher ranking. ( This makes sense to me and it makes it easy for me to let them control the search result relevance ). Here's a simplified query: SELECT p.ProductID AS ContentID , p.ProductName AS Title , p.ProductCode AS Subtitle , 100 AS Rank , p.ProductKeywords AS Keywords FROM Products AS p WHERE FREETEXT( p.ProductKeywords, @SearchPredicate ) I'm thinking something along the lines of replacing the RANK with: , 200 - INDEXOF(@SearchTerm) AS Rank This "should" rank the keyword results by their relevance I know INDEXOF isn't a SQL command... but it's something LIKE that I would like to accomplish. Am I approaching this the right way? Is it possible to do something like this? Does this make sense?

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• are these css classes names good?

  - by metal-gear-solid

  See section /* Common Classes */ of this page. http://webdesign.about.com/od/css/a/master_stylesht_2.htm are these css classes good, to use in any project? in terms of semantic? /* Common Classes */ .clear { clear: both; } .floatLeft { float: left; } .floatRight { float: right; } .textLeft { text-align: left; } .textRight { text-align: right; } .textCenter { text-align: center; } .textJustify { text-align: justify; } .blockCenter { display: block; margin-left: auto; margin-right: auto; } /* remember to set width */ .bold { font-weight: bold; } .italic { font-style: italic; } .underline { text-decoration: underline; } .noindent { margin-left: 0; padding-left: 0; } .nomargin { margin: 0; } .nopadding { padding: 0; } .nobullet { list-style: none; list-style-image: none; }

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• What's the most DRY-appropriate way to execute an SQL command?

  - by Sean U

  I'm looking to figure out the best way to execute a database query using the least amount of boilerplate code. The method suggested in the SqlCommand documentation: private static void ReadOrderData(string connectionString) { string queryString = "SELECT OrderID, CustomerID FROM dbo.Orders;"; using (SqlConnection connection = new SqlConnection(connectionString)) { SqlCommand command = new SqlCommand(queryString, connection); connection.Open(); SqlDataReader reader = command.ExecuteReader(); try { while (reader.Read()) { Console.WriteLine(String.Format("{0}, {1}", reader[0], reader[1])); } } finally { reader.Close(); } } } mostly consists of code that would have to be repeated in every method that interacts with the database. I'm already in the habit of factoring out the establishment of a connection, which would yield code more like the following. (I'm also modifying it so that it returns data, in order to make the example a bit less trivial.) private SQLConnection CreateConnection() { var connection = new SqlConnection(_connectionString); connection.Open(); return connection; } private List<int> ReadOrderData() { using(var connection = CreateConnection()) using(var command = connection.CreateCommand()) { command.CommandText = "SELECT OrderID FROM dbo.Orders;"; using(var reader = command.ExecuteReader()) { var results = new List<int>(); while(reader.Read()) results.Add(reader.GetInt32(0)); return results; } } } That's an improvement, but there's still enough boilerplate to nag at me. Can this be reduced further? In particular, I'd like to do something about the first two lines of the procedure. I don't feel like the method should be in charge of creating the SqlCommand. It's a tiny piece of repetition as it is in the example, but it seems to grow if transactions are being managed manually or timeouts are being altered or anything like that.

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• Hashing the state of a complex object in .NET

  - by Jan

  Some background information: I am working on a C#/WPF application, which basically is about creating, editing, saving and loading some data model. The data model contains of a hierarchy of various objects. There is a "root" object of class A, which has a list of objects of class B, which each has a list of objects of class C, etc. Around 30 classes involved in total. Now my problem is that I want to prompt the user with the usual "you have unsaved changes, save?" dialog, if he tries to exit the program. But how do I know if the data in current loaded model is actually changed? There is of course ways to solve this, like e.g. reloading the model from file and compare against the one in memory value by value or make every UI control set a flag indicating the model has been changed. Now instead, I want to create a hash value based on the model state on load and generate a new value when the user tries to exit, and compare those two. Now the question: So inspired of that, I was wondering if there exist some way to generate a hash value from the (value)state of some arbitrary complex object? Preferably in a generic way, e.g. no need to apply attributes to each involved class/field. One idea could be to use some of .NET's serialization functionality (assuming it will work out-of-the-box in this case) and apply a hash function to the content of the resulting file. However, I guess there exist some more suitable approach. Thanks in advance.

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• How can I make this LinqToSQL query work? (SqlExecption)

  - by kversch

  The following code gives me an SqlException: OO theCourse = subject.Course; var students = dc.studentsCourses.Where(x = x.course == theCourse).Select(x = x.student); "Invalid object name 'dbo.studentsCourses'." I tried the following code instead but I also get an Exception. My original question was asked on Aardvark and can be read bellow: var allStudents = from s in dc.students select s; List thestudents = new List(); foreach (student s in allStudents) { if (s.courses.Contains(theCourse)) { thestudents.Add(s); } } I did a right click, "run custom tool" on my dbml and checked my names of my tables and entities. The project compiles but I get an Exception at runtime on this line: "if (s.courses.Contains(theCourse))" Any ideas? Original question on Aardvark: How do I do a LinqToSQL query that gives me this: I want to select all students that attended a certain lesson. The lesson is from a certain course. So select the course the lesson is from. Now select all the students that are following that course. There is a many-to-many relationship between the students and the courses table in my DB. I already extended my LINQ entities to be able to select student.Courses and course.Students using this method: http://www.codeproject.com/KB/linq/linq-to-sql-many-to-many.aspx

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• incremental way of counting quantiles for large set of data

  - by Gacek

  I need to count the quantiles for a large set of data. Let's assume we can get the data only through some portions (i.e. one row of a large matrix). To count the Q3 quantile one need to get all the portions of the data and store it somewhere, then sort it and count the quantile: List<double> allData = new List<double>(); foreach(var row in matrix) // this is only example. In fact the portions of data are not rows of some matrix { allData.AddRange(row); } allData.Sort(); double p = 0.75*allData.Count; int idQ3 = (int)Math.Ceiling(p) - 1; double Q3 = allData[idQ3]; Now, I would like to find a way of counting this without storing the data in some separate variable. The best solution would be to count some parameters od mid-results for first row and then adjust it step by step for next rows. Note: These datasets are really big (ca 5000 elements in each row) The Q3 can be estimated, it doesn't have to be an exact value. I call the portions of data "rows", but they can have different leghts! Usually it varies not so much (+/- few hundred samples) but it varies! This question is similar to this one: http://stackoverflow.com/questions/1058813/on-line-iterator-algorithms-for-estimating-statistical-median-mode-skewness But I need to count quantiles. ALso there are few articles in this topic, i.e.: http://web.cs.wpi.edu/~hofri/medsel.pdf http://portal.acm.org/citation.cfm?id=347195&dl But before I would try to implement these, I wanted to ask you if there are maybe any other, qucker ways of counting the 0.25/0.75 quantiles?

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• How do I make JPA POJO classes + Netbeans forms play well together?

  - by Zak

  I started using netbeans to design forms to edit the instances of various classes I have made in a small app I am writing. Basically, the app starts, an initial set of objects is selected from the DB and presented in a list, then an item in the list can be selected for editing. When the editor comes up it has form fields for many of the data fields in the class. The problem I run into is that I have to create a controller that maps each of the data elements to the correct form element, and create an inordinate number of small conversion mapping lines of code to convert numbers into strings and set the correct element in a dropdown, then another inordinate amount of code to go back and update the underlying object with all the values from the form when the save button is clicked. My question is; is there a more directly way to make the editing of the form directly modify the contents of my class instance? I would like to be able to have a default mapping "controller" that I can configure, then override the getter/setter for a particular field if needed. Ideally, there would be standard field validation for things like phone numbers, integers, floats, zip codes, etc... I'm not averse to writing this myself, I would just like to see if it is already out there and use the right tool for the right job.

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• Django: DatabaseError column does not exist

  - by Rosarch

  I'm having a problem with Django 1.2.4. Here is a model: class Foo(models.Model): # ... ftw = models.CharField(blank=True) bar = models.ForeignKey(Bar) Right after flushing the database, I use the shell: Python 2.6.6 (r266:84292, Sep 15 2010, 15:52:39) [GCC 4.4.5] on linux2 Type "help", "copyright", "credits" or "license" for more information. (InteractiveConsole) >>> from apps.foo.models import Foo >>> Foo.objects.all() Traceback (most recent call last): File "<console>", line 1, in <module> File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 67, in __repr__ data = list(self[:REPR_OUTPUT_SIZE + 1]) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 82, in __len__ self._result_cache.extend(list(self._iter)) File "/usr/local/lib/python2.6/dist-packages/django/db/models/query.py", line 271, in iterator for row in compiler.results_iter(): File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/compiler.py", line 677, in results_iter for rows in self.execute_sql(MULTI): File "/usr/local/lib/python2.6/dist-packages/django/db/models/sql/compiler.py", line 732, in execute_sql cursor.execute(sql, params) File "/usr/local/lib/python2.6/dist-packages/django/db/backends/util.py", line 15, in execute return self.cursor.execute(sql, params) File "/usr/local/lib/python2.6/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 44, in execute return self.cursor.execute(query, args) DatabaseError: column foo_foo.bar_id does not exist LINE 1: ...t_omg", "foo_foo"."ftw", "foo_foo... What am I doing wrong here?

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• Is there unreachable code in this snippet? I don't think so, but Resharper is telling me otherwise.

  - by The Matt

  I have the following method I came across in a code review. Inside the loop Resharper is telling me that if (narrativefound == false) is incorrect becuase narrativeFound is always true. I don't think this is the case, because in order to set narrativeFound to true it has to pass the conditional string compare first, so how can it always be true? Am I missing something? Is this a bug in Resharper or in our code? public Chassis GetChassisForElcomp(SPPA.Domain.ChassisData.Chassis asMaintained, SPPA.Domain.ChassisData.Chassis newChassis) { Chassis c = asMaintained; List<Narrative> newNarrativeList = new List<Narrative>(); foreach (Narrative newNarrative in newChassis.Narratives) { bool narrativefound = false; foreach (Narrative orig in asMaintained.Narratives) { if (string.Compare(orig.PCode, newNarrative.PCode) ==0 ) { narrativefound = true; if (newNarrative.NarrativeValue.Trim().Length != 0) { orig.NarrativeValue = newNarrative.NarrativeValue; newNarrativeList.Add(orig); } break; } if (narrativefound == false) { newNarrativeList.Add(newNarrative); } } } c.SalesCodes = newChassis.SalesCodes; c.Narratives = newNarrativeList; return c; }

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• Problem declaring and calling internal metthods

  - by Martin

  How do I declare and use small helper functions inside my normal methods ? In on of my objective-c methods I need a function to find an item within a string -(void) Onlookjson:(id) sender{ NSString * res = getKeyValue(res, @"Birth"); } I came up with a normal C type declaration for helper function getKeyvalue like this NSString * getKeyvalue(NSString * s, NSString key){ NSString *trm = [[s substringFromIndex:2] substringToIndex:[s length]-3]; NSArray *list = [trm componentsSeparatedByString:@";"]; .... NSString res; res = [list objectAtIndex:1]; ... return res; } Input data string: { Birth = ".."; Death = "..."; ... } Anyway I get an exception "unrecognized selector sent to instance" for any of the two first lines in the helper function How do I declare helper functions that are just to be used internally and how to call them safely ? regards Martin

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• What if a large number of objects are passed to my SwingWorker.process() method?

  - by Trejkaz

  I just found an interesting situation. Suppose you have some SwingWorker (I've made this one vaguely reminiscent of my own): public class AddressTreeBuildingWorker extends SwingWorker<Void, NodePair> { private DefaultTreeModel model; public AddressTreeBuildingWorker(DefaultTreeModel model) { } @Override protected Void doInBackground() { // Omitted; performs variable processing to build a tree of address nodes. } @Override protected void process(List<NodePair> chunks) { for (NodePair pair : chunks) { // Actually the real thing inserts in order. model.insertNodeInto(parent, child, parent.getChildCount()); } } private static class NodePair { private final DefaultMutableTreeNode parent; private final DefaultMutableTreeNode child; private NodePair(DefaultMutableTreeNode parent, DefaultMutableTreeNode child) { this.parent = parent; this.child = child; } } } If the work done in the background is significant then things work well - process() is called with relatively small lists of objects and everything is happy. Problem is, if the work done in the background is suddenly insignificant for whatever reason, process() receives a huge list of objects (I have seen 1,000,000, for instance) and by the time you process each object, you have spent 20 seconds on the Event Dispatch Thread, exactly what SwingWorker was designed to avoid. In case it isn't clear, both of these occur on the same SwingWorker class for me - it depends on the input data, and the type of processing the caller wanted. Is there a proper way to handle this? Obviously I can intentionally delay or yield the background processing thread so that a smaller number might arrive each time, but this doesn't feel like the right solution to me.

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• How can I implement an interface member in protected ?

  - by Nicolas Dorier

  Hi, I've been quite surprise when I saw the metadata of ReadOnlyObservableCollection in VS 2008... public class ReadOnlyObservableCollection<T> : ReadOnlyCollection<T>, INotifyCollectionChanged, INotifyPropertyChanged { // Summary: // Initializes a new instance of the System.Collections.ObjectModel.ReadOnlyObservableCollection<T> // class that serves as a wrapper for the specified System.Collections.ObjectModel.ObservableCollection<T>. // // Parameters: // list: // The collection to wrap. public ReadOnlyObservableCollection(ObservableCollection<T> list); // Summary: // Occurs when an item is added or removed. protected virtual event NotifyCollectionChangedEventHandler CollectionChanged; // // Summary: // Occurs when a property value changes. protected virtual event PropertyChangedEventHandler PropertyChanged; // Summary: // Raises the System.Collections.ObjectModel.ReadOnlyObservableCollection<T>.CollectionChanged // event. // // Parameters: // args: // The event data. protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs args); // // Summary: // Raises the System.Collections.ObjectModel.ReadOnlyObservableCollection<T>.PropertyChanged // event. // // Parameters: // args: // The event data. protected virtual void OnPropertyChanged(PropertyChangedEventArgs args); } As you can see, CollectionChanged, a member of INotifyCollectionChanged is implemented in protected... and I can't do that in my own class. .NET framework should not compile ! Does someone has an explanation of this mystery ?

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• Node & Redis: Crucial Design Issues in Production Mode

  - by Ali

  This question is a hybrid one, being both technical and system design related. I'm developing the backend of an application that will handle approx. 4K request per second. We are using Node.js being super fast and in terms of our database struction we are using MongoDB, with Redis being a layer between Node and MongoDB handling volatile operations. I'm quite stressed because we are expecting concurrent requests that we need to handle carefully and we are quite close to launch. However I do not believe I've applied the correct approach on redis. I have a class Student, and they constantly change stages(such as 'active', 'doing homework','in lesson' etc. Thus I created a Redis DB for each state. (1 for being 'active', 2 for being 'doing homework'). Above I have the structure of the 'active' students table; xa5p - JSON stringified object #1 pQrW - JSON stringified object #2 active_student_table - {{studentId:'xa5p'}, {studentId:'pQrW'}} Since there is no 'select all keys method' in Redis, I've been suggested to use a set such that when I run command 'smembers' I receive the keys and later on do 'get' for each id in order to find a specific user (lets say that age older than 15). I've been also suggested that in fact I used never use keys in production mode. My question is, no matter how 'conceptual' it is, what specific things I should avoid doing in Node & Redis in production stage?. Are they any issues related to my design? Students must be objects and I sure can list them in a list but I haven't done yet. Is it that crucial in production stage?

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• In a combobox, how do I determine the highlighted item (not selected item)?

  - by Harold Bamford

  First, fair warning: I am a complete newbie with C# and WPF. I have a combobox (editable, searchable) and I would like to be able to intercept the Delete key and remove the currently highlighted item from the list. The behavior I'm looking for is like that of MS Outlook when entering in email addresses. When you give a few characters, a dropdown list of potential matches is displayed. If you move to one of these (with the arrow keys) and hit Delete, that entry is permanently removed. I want to do that with an entry in the combobox. Here is the XAML (simplified): <ComboBox x:Name="Directory" KeyUp="Directory_KeyUp" IsTextSearchEnabled="True" IsEditable="True" Text="{Binding Path=CurrentDirectory, Mode=TwoWay}" ItemsSource="{Binding Source={x:Static self:Properties.Settings.Default}, Path=DirectoryList, Mode=TwoWay}" / The handler is: private void Directory_KeyUp(object sender, KeyEventArgs e) { ComboBox box = sender as ComboBox; if (box.IsDropDownOpen && (e.Key == Key.Delete)) { TrimCombobox("DirectoryList", box.HighlightedItem); // won't compile! } } When using the debugger, I can see box.HighlightedItem has the value I want but when I try and put in that code, it fails to compile with: System.Windows.Controls.ComboBox' does not contain a definition for 'HighlightedItem'... So: how do I access that value? Keep in mind that the item has not been selected. It is merely highlighted as the mouse hovers over it. Thanks for your help.

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• ASP:GridView does not show data with ObjectdataSource

  - by Kashif

  I have been trying to bind a DataGrid with ObjectDataSource having custom paging but no output is display on my usercontrol. Here is the code I am using <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="LeadId" DataSourceID="dsBuyingLead1" AllowPaging="True"> <Columns> <asp:BoundField DataField="Subject" HeaderText="Subject" ReadOnly="True" /> <asp:BoundField DataField="ExpiryDate" HeaderText="ExpiryDate" ReadOnly="True" /> </Columns> </asp:GridView> <asp:ObjectDataSource ID="dsBuyingLead1" runat="server" EnablePaging="True" DataObjectTypeName="Modules.SearchBuyingLeadInfo" OldValuesParameterFormatString="original_{0}" SelectMethod="GetAllBuyingLeads" StartRowIndexParameterName="startRow" MaximumRowsParameterName="maximumRows" SelectCountMethod="GetAllBuyingLeadsCount" TypeName="Modules.SearchController"> <SelectParameters> <asp:QueryStringParameter Name="searchText" QueryStringField="q" Type="String" /> </SelectParameters> </asp:ObjectDataSource> Here are my methods from SearchController class: [DataObjectMethod(DataObjectMethodType.Select)] public static long GetAllBuyingLeadsCount(string searchText) { return DataProvider.Instance().GetAllBuyingLeadsCount(searchText); } [DataObjectMethod(DataObjectMethodType.Select)] public static List<SearchBuyingLeadInfo> GetAllBuyingLeads (string searchText, int startRow, int maximumRows) { List<SearchBuyingLeadInfo> l = CBO.FillCollection<SearchBuyingLeadInfo> ( DataProvider.Instance() .GetAllBuyingLeadswithText(searchText, startRow, maximumRows) ); return l; } Where SearchBuyingLeadInfo is my Data Access Object class I have verified by setting up break points that both GetAllBuyingLeadsCount and GetAllBuyingLeads return non-zero values but unfortunately nothing is displayed on the grid. Only the column headers are displayed. Can anyone tell me what am I missing?

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