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  • gridviev add new row problem

    - by Dominating
    My relation is from two tables - table A and table B. B has fk ID pointing to A.ID. In gridview for sourse i have choosen A. When I append new row in A its ok.. But with this action I want to add new row in B too and init it with some values which are copies from row number Row given as argument in PasteCopy private void PasteCopy(int Row) { XPDataTableObject forCopy = gridView1.GetRow(Row) as XPDataTableObject; gridViewEcnMaster.AddNewRow(); XPDataTableObject toCopy = gridView1.GetRow(GridControl.NewItemRowHandle) as XPDataTableObject; SetA(forCopy);// working SetB(ref toCopy, forCopy); XPDataTableObject toCopy1 = gridView1.GetFocusedRow() as XPDataTableObject; XPCollection historyForCopy = toCopy1.GetMemberValue("FK___B__ID") as XPCollection; foreach (XPDataTableObject item in historyForCopy) { MessageBox.Show(item.GetMemberValue("USER").ToString()); } } public void SetB(ref XPDataTableObject toCopy, XPDataTableObject forCopy) { XPCollection historyToCopy = toCopy.GetMemberValue("FK__B__ID") as XPCollection; XPCollection historyForCopy = forCopy.GetMemberValue("FK__B__ID") as XPCollection; XPClassInfo cinfo = session.GetClassInfo(typeof(SPM_ECN_DataSet.BDataTable)); foreach (XPDataTableObject item in historyForCopy) { XPDataTableObject historyRecord = new XPDataTableObject(session, cinfo); historyRecord.SetMemberValue("USER", GetCurWinUser().ToString()); historyRecord.SetMemberValue("ID", forCopy.GetMemberValue("ID"));//if not set == null historyToCopy.Add(historyRecord); } } public void SetA(XPDataTableObject forCopy) { gridView1.SetFocusedRowCellValue("VERSION", 1); } What is wrong with this? why its locking all my application after i do this?

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  • How to make UISlider output nice rounded numbers exponentially?

    - by RickiG
    Hi I am implementing a UISlider a user can manipulate to set a distance. I have never used the CocoaTouch UISlider, but have used other frameworks sliders, usually there is a variable for setting the "step" and other "helper" properties. The documentation for the UISlider deals only with a max and min value, and the output is always a 6 decimal float with a linear relation to the position of the "slider nob". I guess I will have to implement the desired functionality step by step. To the user, the min/max values range from 10 m to 999 Km, I am trying to implement this in an exponential way, that will feel natural to the user. I.e. the user experiences a feeling of control over the values, big or small. Also that the "output" has reasonable values. Values like 10m 200m 2.5km 150 km etc. instead of 1.2342356 m or 108.93837756 km. I would like for the step size to increase by 10m for the first 200m, then maybe by 50m up to 500m, then when passing the 1000 m value, it starts to deal with Kilometers, so then it is step size = 1 km up until 50 km, then maybe 25 km steps etc. Any way I go about this I end up doing a lot of rounding and a lot of calculations wrapped in a forrest of if statements and NSString/Number conversions, each time the user moves the slider just a little. I was hoping someone could lend me a bit of inspiration/math help or make me aware of a more lean approach to solving this problem. My last idea is to populate and array with a 100 string values, then have the slider int value correspond to a string, this is not very flexible, but doable. Thank you in advance for any help given:)

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  • Why delete-orphan needs "cascade all" to run in JPA/Hibernate ?

    - by Jerome C.
    Hello, I try to map a one-to-many relation with cascade "remove" (jpa) and "delete-orphan", because I don't want children to be saved or persist when the parent is saved or persist (security reasons due to client to server (GWT, Gilead)) But this configuration doesn't work. When I try with cascade "all", it runs. Why the delete-orphan option needs a cascade "all" to run ? here is the code (without id or other fields for simplicity, the class Thread defines a simple many-to-one property without cascade): when using the removeThread function in a transactional function, it does not run but if I edit cascade.Remove into cascade.All, it runs. @Entity public class Forum { private List<ForumThread> threads; /** * @return the topics */ @OneToMany(mappedBy = "parent", cascade = CascadeType.REMOVE, fetch = FetchType.LAZY) @Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN) public List<ForumThread> getThreads() { return threads; } /** * @param topics the topics to set */ public void setThreads(List<ForumThread> threads) { this.threads = threads; } public void addThread(ForumThread thread) { getThreads().add(thread); thread.setParent(this); } public void removeThread(ForumThread thread) { getThreads().remove(thread); } } thanks.

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  • css problem - 'post link'

    - by csetzkorn
    Hi, I am no css expert so I am wondering whether someone could help. I have several forms to delete an item like this: <form action="/Items/DeleteItem" class="deleteForm" method="post"> Some text <input id="Id" name="Id" value="14014" type="hidden"> <input value="Delete" class="link_button" type="submit"> </form> This should look like this: Some text Delete Here ‘Some text’ describes the item and Delete is a ‘link’ which performs a post request to delete the item (as virtually all browsers only support the post and get requests). I have started to style things (CSS below) but the ‘Delete’ ‘link’ is still slightly offset in relation to ‘Some text’ (at least in firefox). I would appreciate any help with the css. Thanks! .link_button { background-color:white; border:0; color:#034af3; text-decoration:underline; font-size:1em; font-family:inherit; cursor:pointer; float:left; margin:0; padding:0; } .deleteForm { float:right; margin:0; padding:0; } Christian

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  • Java many to many association map

    - by Raphael Jolivet
    Hi, I have to classes, ClassA and ClassB and a "many to many" AssociationClass. I want to use a structure to hold the associations between A and B such as I can know, for each instance of A or B, which are their counterparts. I thought of using a Hashmap, with pair keys: Hasmap<Pair<ClassA, ClassB>, AssociationClass> associations; This way, I can add and remove an association between two instances of ClassA and ClassB, and I can query a relation for two given instances. However, I miss the feature of getting all associations defined for a given instance of ClassA or ClassB. I could do it by brute force and loop over all keys of the map to search for associations between a given instance, but this is inefficient and not elegant. Do you know of any data structure / free library that enables this ? I don't want to reinvent the wheel. Thanks in advance for your help, Raphael NB: This is not a "database" question. These objects are pure POJO used for live computation, I don't need persistence stuff.

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  • howto distinguish composition and self-typing use-cases

    - by ayvango
    Scala has two instruments for expressing object composition: original self-type concept and well known trivial composition. I'm curios what situations I should use which in. There are obvious differences in their applicability. Self-type requires you to use traits. Object composition allows you to change extensions on run-time with var declaration. Leaving technical details behind I can figure two indicators to help with classification of use cases. If some object used as combinator for a complex structure such as tree or just have several similar typed parts (1 car to 4 wheels relation) than it should use composition. There is extreme opposite use case. Lets assume one trait become too big to clearly observe it and it got split. It is quite natural that you should use self-types for this case. That rules are not absolute. You may do extra work to convert code between this techniques. e.g. you may replace 4 wheels composition with self-typing over Product4. You may use Cake[T <: MyType] {part : MyType} instead of Cake { this : MyType => } for cake pattern dependencies. But both cases seem counterintuitive and give you extra work. There are plenty of boundary use cases although. One-to-one relations is very hard to decide with. Is there any simple rule to decide what kind of technique is preferable? self-type makes you classes abstract, composition makes your code verbose. self-type gives your problems with blending namespaces and also gives you extra typing for free (you got not just a cocktail of two elements but gasoline-motor oil cocktail known as a petrol bomb). How can I choose between them? What hints are there? Update: Let us discuss the following example: Adapter pattern. What benefits it has with both selt-typing and composition approaches?

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  • What are the options for overriding Django's cascading delete behaviour?

    - by Tom
    Django models generally handle the ON DELETE CASCADE behaviour quite adequately (in a way that works on databases that don't support it natively.) However, I'm struggling to discover what is the best way to override this behaviour where it is not appropriate, in the following scenarios for example: ON DELETE RESTRICT (i.e. prevent deleting an object if it has child records) ON DELETE SET NULL (i.e. don't delete a child record, but set it's parent key to NULL instead to break the relationship) Update other related data when a record is deleted (e.g. deleting an uploaded image file) The following are the potential ways to achieve these that I am aware of: Override the model's delete() method. While this sort of works, it is sidestepped when the records are deleted via a QuerySet. Also, every model's delete() must be overridden to make sure Django's code is never called and super() can't be called as it may use a QuerySet to delete child objects. Use signals. This seems to be ideal as they are called when directly deleting the model or deleting via a QuerySet. However, there is no possibility to prevent a child object from being deleted so it is not usable to implement ON CASCADE RESTRICT or SET NULL. Use a database engine that handles this properly (what does Django do in this case?) Wait until Django supports it (and live with bugs until then...) It seems like the first option is the only viable one, but it's ugly, throws the baby out with the bath water, and risks missing something when a new model/relation is added. Am I missing something? Any recommendations?

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  • C# parameters by reference and .net garbage collection

    - by Yarko
    I have been trying to figure out the intricacies of the .NET garbage collection system and I have a question related to C# reference parameters. If I understand correctly, variables defined in a method are stored on the stack and are not affected by garbage collection. So, in this example: public class Test { public Test() { } public int DoIt() { int t = 7; Increment(ref t); return t; } private int Increment(ref int p) { p++; } } the return value of DoIt() will be 8. Since the location of t is on the stack, then that memory cannot be garbage collected or compacted and the reference variable in Increment() will always point to the proper contents of t. However, suppose we have: public class Test { private int t = 7; public Test() { } public int DoIt() { Increment(ref t); return t; } private int Increment(ref int p) { p++; } } Now, t is stored on the heap as it is a value of a specific instance of my class. Isn't this possibly a problem if I pass this value as a reference parameter? If I pass t as a reference parameter, p will point to the current location of t. However, if the garbage collector moves this object during a compact, won't that mess up the reference to t in Increment()? Or does the garbage collector update even references created by passing reference parameters? Do I have to worry about this at all? The only mention of worrying about memory being compacted on MSDN (that I can find) is in relation to passing managed references to unmanaged code. Hopefully that's because I don't have to worry about any managed references in managed code. :)

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  • Is ADO.NET Entity framework database schema update possible ?

    - by fyasar
    Hi All I'm working on proof of concept application like crm and i need your some advice. My application's data layer completely dynamic and run onto EF 3.5. When the user update the entity, change relation or add new column to the database, first i'm planning make for these with custom classes. After I rebuild my database model layer with new changes during the application runtime. And my model layer tie with tightly coupled to my project for easy reflecting model layer changes (It connected to my project via interfaces and loading onto to application domain in the runtime). I need to create dynamic entities, create entity relations and modify them during the runtime after that i need to create change database script for updating database schema. I know ADO.NET team says "we will be able to provide this property in EF 4.0", but i don't need to wait for them. How can i update database changes during the runtime via EF 3.5 ? For example, i need to create new entity or need to change some entity schema, add new properties or change property types after than how can apply these changes on the physical database schema ? Any ideas ?

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  • How VerticalOffset changes when Scrollable height changes while having list inside a list

    - by Prakash
    I am making a WP7 app which has a Listbox of UserControls. Each UserControl has an ItemsControl and Button(for getting more results). On click of the button the ItemsControl items will be increased by 5 or 10. Now on clicking on the GetMore button of any of the usercontrols except the first or last, there will be an increase in Scrollable height(Total height of the listbox) of the ListBox but the VerticalOffset(position of scrollbar from top) of the ListBox remains same. Now the problem I am facing is that the Vertical Offset is not absolute but relative to Scrollable Height. So the content being viewed till then will be changed basing on the new value of ScollableHeight. I want to know the relation between them, so that I can do some math and set the VerticalOffset value. I have added some dependency properties on VerticalOffset and ScrollableHeight through which I can get the events when any of them is changed. Also trying to use them to readjust the VerticalOffset. Any suggestions or corrections are highly appreciated.

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  • How can I create a properly sizing QWebView?

    - by chacham15
    I want to make a QWebView appear expanding to the width and height so that ideally it will have no scroll bars. Some websites may have fixed widths that wont allow this, but I am not concerned with those. In any case, I cannot do as I wish because QWebView implements sizeHint as follows: QSize QWebView::sizeHint() const { return QSize(800, 600); // ####... } This is incorrect on a number of levels. 1. It doesnt at all take into account the size of the actual web page. 2. It doesnt take into account that the height and width are related to each other. (To prove #2 think about text in web pages that wraps to the next line.) As a simple fix I tried to do (where QResizingWebView extends QWebView): QSize QResizingWebView::sizeHint() const{ return this-page()-mainFrame()-contentsSize(); } While this is closer to the result, it also has 2 flaws. 1. It doesnt take into account the relation between the displayed width/height. 2. this->page()->mainFrame()->contentsSize() is inaccurate from what I can tell from my preliminary testing (it has returned heights larger than it should under many cases, although this may be related to #1). Does anyone have any tips to fix this?

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  • How can I provide users with the functionality of the DBUnit DatabaseOperation methods from a web in

    - by reckoner
    I am currently updating a java-based web application which allows database developers to create stored procedure regression test suites for database testing. Currently, for test setup, execution and clean-up stages, the user is provided with text boxes where they are able to enter SQL code which is executed by the isql command. I would like to extend the application to use DB Unit’s DatabaseOperation methods to provide more ways to setup the state of the database than just SQL statements. The main reason for using Db Unit rather than just SQL statements is to be able to create and store xml and xls DataSets on a server where they can be associated with their test cases and used for data setup. My question is: How can I provide users with the functionality of the DBUnit DatabaseOperation methods from a web interface? I have considered: Creating a simple programming language and a parser to read some simple syntax involving the DB Unit method names which accept a parameter being the file location to an xml or xls DataSet. I was thinking of allowing the user to register the files they need with the web app which would catalogue them and provide each file with an identifier which could passed as a parameter to the methods in this simple programming language. Creating an XML DTD which provides the user with the ability to specify operations and parameters. If I went this approach, how can I execute the methods and their parameters that I parse from the XML document? Creating a table in the database which stores the method and a FK relation to a catalogued DataSet file, however I don’t think this would be good solution due to the fact that data entry would be tedious. Thanks for your help.

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  • symfony doctrine build-sql error

    - by user313571
    I have some big problems with symfony and doctrine at the beginning of a new project. I have created database diagram with mysql workbench, inserted the sql into phpmyadmin and then I've tried symfony doctrine:build-schema to generate the YAML schema. It generates a wrong schema (relations don't have on delete/on update) and after this I've tried symfony doctrine:build --sql and symfony doctrine:insert-sql The insert-sql statement generates error (can't create table ... failing query alter table add constraint ....), so I've decided to take a look over the generated sql and I've found out some differences between the sql generated from mysql workbench (which works perfect, including relations) and the sql generated by doctrine. I'll be short from now: I have to tables, EVENT and FORM and a 1 to n relation (each event may have multiple forms) so the correct constraint (generated with workbench) is ALTER TABLE `form` ADD CONSTRAINT `fk_form_event1` FOREIGN KEY (`event_id`) REFERENCES `event` (`id`) ON DELETE CASCADE ON UPDATE CASCADE; doctrine generated statement is: ALTER TABLE event ADD CONSTRAINT event_id_form_event_id FOREIGN KEY (id) REFERENCES form(event_id); It's totally reversed and I am sure here is the error. What should I do? It's also correct like this?

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  • SQLAlchemy - relationship limited on more than just the foreign key

    - by Marian
    I have a wiki db layout with Page and Revisions. Each Revision has a page_id referencing the Page, a page relationship to the referenced page; each Page has a all_revisions relationship to all its revisions. So far so common. But I want to implement different epochs for the pages: If a page was deleted and is recreated, the new revisions have a new epoch. To help find the correct revisions, each page has a current_epoch field. Now I want to provide a revisions relation on the page that only contains its revisions, but only those where the epochs match. This is what I've tried: revisions = relationship('Revision', primaryjoin = and_( 'Page.id == Revision.page_id', 'Page.current_epoch == Revision.epoch', ), foreign_keys=['Page.id', 'Page.current_epoch'] ) Full code (you may run that as it is) However this always raises ArgumentError: Could not determine relationship direction for primaryjoin condition ...`, I've tried all I had come to mind, it didn't work. What am I doing wrong? Is this a bad approach for doing this, how could it be done other than with a relationship?

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  • SQL Server search filter and order by performance issues

    - by John Leidegren
    We have a table value function that returns a list of people you may access, and we have a relation between a search and a person called search result. What we want to do is that wan't to select all people from the search and present them. The query looks like this SELECT qm.PersonID, p.FullName FROM QueryMembership qm INNER JOIN dbo.GetPersonAccess(1) ON GetPersonAccess.PersonID = qm.PersonID INNER JOIN Person p ON p.PersonID = qm.PersonID WHERE qm.QueryID = 1234 There are only 25 rows with QueryID=1234 but there are almost 5 million rows total in the QueryMembership table. The person table has about 40K people in it. QueryID is not a PK, but it is an index. The query plan tells me 97% of the total cost is spent doing "Key Lookup" witht the seek predicate. QueryMembershipID = Scalar Operator (QueryMembership.QueryMembershipID as QM.QueryMembershipID) Why is the PK in there when it's not used in the query at all? and why is it taking so long time? The number of people total 25, with the index, this should be a table scan for all the QueryMembership rows that have QueryID=1234 and then a JOIN on the 25 people that exists in the table value function. Which btw only have to be evaluated once and completes in less than 1 second.

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  • Custom Detail in Linq-to-SQL Master-Detail DataGridViews

    - by Andres
    Hi, looking for a way to create Linq-to-SQL Master-Detail WinForms DataGridViews where the Detail part of the Linq query is a custom one. Can do fine this: DataClasses1DataContext db = new DataClasses1DataContext(".\\SQLExpress"); var myQuery = from o in db.Orders select o; dataGridView1.DataSource = new BindingSource() { DataSource = myQuery }; dataGridView2.DataSource = new BindingSource() { DataSource = dataGridView1.DataSource, DataMember = "OrderDetails" }; but I'd like to have the Detail part under my precise control, like var myQuery = from o in db.Orders join od in db.OrderDetails on o.ID equals od.OrderID into MyOwnSubQuery select o; and use it for the second grid: dataGridView2.DataSource = new BindingSource() { DataSource = dataGridView1.DataSource, DataMember = "MyOwnSubQuery" // not working... }; the real reason I want it is a bit more complex (I'd like to have the Detail part to be some not-pre-defined join actually), but I'm hoping the above conveyed the idea. Can I only have the Detail part as a plain sub-table coming out of the pre-defined relation or can I do more complex stuff with the Detail part? Does anyone else feel this is kind of limited (if the first example is the best we can do)? Thanks!

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  • How to update non-scalar entity properties in EF 4.0?

    - by Mike
    At first I was using this as an extension method to update my detached entities... Public Sub AttachUpdated(ByVal obj As ObjectContext, ByVal objectDetached As EntityObject) If objectDetached.EntityState = EntityState.Detached Then Dim original As Object = Nothing If obj.TryGetObjectByKey(objectDetached.EntityKey, original) Then obj.ApplyCurrentValues(objectDetached.EntityKey.EntitySetName, objectDetached) Else Throw New ObjectNotFoundException() End If End If End Sub Everything has been working great until I had to update non-scalar properties. Correct me if I am wrong but that is because "ApplyCurrentValues" only supports scalars. To get around this I was just saving the FK_ID field instead of the entity object relation. Now I am faced with a many to many relationship so its not that simple. I would like to do something like this... Dim Resource = RelatedResource.GetByID(item.Value) Condition.RelatedResources.Add(Resource) But when I call SaveChanges the added Resources aren't saved. I started to play around with self-tracking entities (not sure if they will help solve my prob) but it seems they cannot be serialized to ViewState and this is a requirement for me. I guess one solution would be to add the xRef table as an entity and add the fks myself but I would rather it just work how I expect it too. I am open to any suggestions on how to either save my many to many relationships or serialize self-tracking entities (if self-trackingwould even solve my problem). Thanks!

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  • Sync Framework Considerations for Smart Client app

    - by DarkwingDuck
    Microsoft Sync Framework with SQL 2005? Is it possible? It seems to hint that the OOTB providers use SQL2008 functionality. I'm looking for some quick wins in relation to a sync project. The client app will be offline for a number of days. There will be a central server that MUST be SQL Server 2005. I can use .net 3.5. Basically the client app could go offline for a week. When it comes back online it needs to sync its data. But the good thing is that the data only needs to push to the server. The stuff that syncs back to the client will just be lookup data which the client never changes. So this means I don't care about sync collisions. To simplify the scenario for you, this smart client goes offline and the user surveys data about some observations. They enter the data into the system. When the laptop is reconnected to the network, it syncs back all that data to the server. There will be other clients doing the same thing too, but no one ever touches each other's data. Then there are some reports on the server for viewing the data that has been pushed to the server. This also needs to use ClickOnce. My biggest concern is that there is an interim release while a client is offline. This release might require a new field in the database, and a new field to fill in on the survey. Obviously that new field will be nullable because we can't update old data, that's fine to set as an assumption. But when the client connects up and its local data schema and the server schema don't match, will sync framework be able to handle this? After the data is pushed to the server it is discarded locally. Hope my problem makes sense.

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  • FreqTable with random values(#C)

    - by Sef
    Hello, I would like to make a frequency table with random numbers. So i have created a array that generates 11 random values between 0 and 9999. public void FillArrayRandom(int[] T) { Random Rndint = new Random(); for (int i=0; i < T.Length; i++) { T[i] = Rndint.Next(0, 9999); } }/*FillArrayRandom*/ The result i want is something alike this:(bar height up to 21) So this will be a constant. * * * * * * (the highest value will have the largest row/bar) * * * * 0 1 2 3 .....(index value's) 931 6669 10 8899 .... (up to 11 random values) My question is how do i exactly caculate the frequency between those 11 random values? The bars should have a relative relation with each other depending on there frequency. I would only like to use 1 single array in my program (for the generated values). F = (F * 21?) / ...? Really no clue how to obtain the proper results. If a frequency is =21 write * If a frequency is =20 write * If a frequency is =19 write * etc... Regards.

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  • Events and references pattern

    - by serhio
    In a project I have the following relation between BO and GUI By e.g. G could represent a graphic with time lines, C a TimeLine curve, P - points of that curve and T the time that represents each point. Each GUI object is associated with the BO corresponding object. When T changes GUI P captures the Changed event and changes its location. So, when G should be modified, it modifies internally its objects and as result T changes, P moves and the GuiG visually changes, everything is OK. But there is an inconvenient of this architecture... BO should not be recreated, because this will breack the link between BO and GUIO. In particular, GUI P should always have the same reference of T. If in a business logic I do by e.g. P1.T = new T(this.T + 10) GUI_P1 will not move anymore, because it wait an event from the reference of former P1.T object, that does not belongs to P1 anymore. So the solution was to always modify the existing objects, not to recreate it. But here is an other inconvenient: performance. Say I have a ready newC object that should replace the older one. Instead of doing G1.C = newC I should do foreach T in foreach P in C replace with T from P from newC. Is there an other more optimal way to do it?

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  • Simplest PHP Routing framework .. ?

    - by David
    I'm looking for the simplest implementation of a routing framework in PHP, in a typical PHP environment (Running on Apache, or maybe nginx) .. It's the implementation itself I'm mostly interested in, and how you'd accomplish it. I'm thinking it should handle URL's, with the minimal rewriting possible, (is it really a good idea, to have the same entrypoint for all dynamic requests?!), and it should not mess with the querystring, so I should still be able to fetch GET params with $_GET['var'] as you'd usually do.. So far I have only come across .htaccess solutions that puts everything through an index.php, which is sort of okay. Not sure if there are other ways of doing it. How would you "attach" what URL's fit to what controllers, and the relation between them? I've seen different styles. One huge array, with regular expressions and other stuff to contain the mapping. The one I think I like the best is where each controller declares what map it has, and thereby, you won't have one huge "global" map, but a lot of small ones, each neatly separated. So you'd have something like: class Root { public $map = array( 'startpage' => 'ControllerStartPage' ); } class ControllerStartPage { public $map = array( 'welcome' => 'WelcomeControllerPage' ); } // Etc ... Where: 'http://myapp/' // maps to the Root class 'http://myapp/startpage' // maps to the ControllerStartPage class 'http://myapp/startpage/welcome' // maps to the WelcomeControllerPage class 'http://myapp/startpage/?hello=world' // Should of course have $_GET['hello'] == 'world' What do you think? Do you use anything yourself, or have any ideas? I'm not interested in huge frameworks already solving this problem, but the smallest possible implementation you could think of. I'm having a hard time coming up with a solution satisfying enough, for my own taste. There must be something pleasing out there that handles a sane bootstrapping process of a PHP application without trying to pull a big magic hat over your head, and force you to use "their way", or the highway! ;)

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  • Are monads Writer m and Either e categorically dual?

    - by sdcvvc
    I noticed there is a dual relation between Writer m and Either e monads. If m is a monoid, then unit :: () -> m join :: (m,m) -> m can be used to form a monad: return is composition: a -> ((),a) -> (m,a) join is composition: (m,(m,a)) -> ((m,m),a) -> (m,a) The dual of () is Void (empty type), the dual of product is coproduct. Every type e can be given "comonoid" structure: unit :: Void -> e join :: Either e e -> e in the obvious way. Now, return is composition: a -> Either Void a -> Either e a join is composition: Either e (Either e a) -> Either (Either e e) a -> Either e a and this is the Either e monad. The arrows follow exactly the same pattern. Question: Is it possible to write a single generic code that will be able to perform both as Either e and as Writer m depending on the monoid given?

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  • database structure

    - by jindalsyogesh
    I have a table named ActivityRecording. This table currently has 500,000 records. I need to add a lot of new inputs that relates to activityrecording table. The relation of activityrecording with these new input fields is 1 to 0,1. So, what's going to happen on screen is when user fills the ActivityRecording data, he will then be taken to a new page and this page will show a form based on the user's input (from a dropdown named service) in activityrecording. There will 6 different kinds of form (each form will have 7-8 inputs which includes textareas of size 5kb, textboxes and checkboxes). So, for one activityrecording user will fill one out of 6 forms. There are two ways I know (there could be more), I can design the data structure: Add all the inputs from all these 6 forms into the activityrecording table. So, columns belonging to 5 of these forms will be null in this table, only columns belonging to one of the forms will have values The other way would be add 6 new tables (one for each form) and add 6 foreign key columns to activityrecording table. So, out of 6 foreign keys, 5 will be null and one will actually point to a table Which approach is a better data structure design? Please take into consideration that number of rows in this table are 500,000 and are expected to grow at a faster rate now.

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  • Offline Mapping API

    - by Aaron M
    Are there any services available that allow me to manipulate maps in an offline setting? I am working on a project that requires me to take a map and based on features on the map, generate a game world. I have looked at a few of the API's for different providers: Google, ms, etc. The API's I looked seem to be strictly showing a user a map. I am looking for something that allows me to create a derivative of a map (the Gameworld), that will never be seen by the public, and is only used by the game engine. However one caveat is that I would like to be able to link the derivative created for use by the game engine, with something I can show the user. As an example. Think of a cross country racing sim. Users cannot control the vehicles directly in this game, they can only control the cars setup, driver, etc. I create a gameworld from a map. The gameworld data (driver position, etc) is overlayed onto a real map. A race might last several days. The only interaction users have with the real map is viewing their position on the map, and where they are in relation to the others. I don't want to violate the terms of the API here. I read Googles API TOS, and it seems to me that creating the gameworld would violdate their TOS. The features I really need are the following The ability to locate a specific place on the map by lat/long The ability/rights to grab those maps and save them as an image file temporarily for processing The ability/rights to store a gameworld that is based on the real map The ability to show a user a map with an overlay (this is optional. I can use googles API, or any other one that supports lat/long.)

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  • Getting a handle on GIS math, where do I start?

    - by Joshua
    I am in charge of a program that is used to create a set of nodes and paths for consumption by an autonomous ground vehicle. The program keeps track of the locations of all items in its map by indicating the item's position as being x meters north and y meters east of an origin point of 0,0. In the real world, the vehicle knows the location of the origin's lat and long, as it is determined by a dgps system and is accurate down to a couple centimeters. My program is ignorant of any lat long coordinates. It is one of my goals to modify the program to keep track of lat long coords of items in addition to an origin point and items' x,y position in relation to that origin. At first blush, it seems that I am going to modify the program to allow the lat long coords of the origin to be passed in, and after that I desire that the program will automatically calculate the lat long of every item currently in a map. From what I've researched so far, I believe that I will need to figure out the math behind converting to lat long coords from a UTM like projection where I specify the origin points and meridians etc as opposed to whatever is defined already for UTM. I've come to ask of you GIS programmers, am I on the right track? It seems to me like there is so much to wrap ones head around, and I'm not sure if the answer isn't something as simple as, "oh yea theres a conversion from meters to lat long, here" Currently, due to the nature of DGPS, the system really doesn't need to care about locations more than oh, what... 40 km? radius away from the origin. Given this, and the fact that I need to make sure that the error on my coordinates is not greater than .5 meters, do I need anything more complex than a simple lat/long to meters conversion constant? I'm knee deep in materials here. I could use some pointers about what concepts to research. Thanks much!

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