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  • How to configure multiple mappings using FluentHibernate?

    - by chris.baglieri
    First time rocking it with NHibernate/Fluent so apologies in advance if this is a naive question. I have a set of Models I want to map. When I create my session factory I'm trying to do all mappings at once. I am not using auto-mapping (though I may if what I am trying to do ends up being more painful than it ought to be). The problem I am running into is that it seems only the top map is taking. Given the code snippet below and running a unit test that attempts to save 'bar', it fails and checking the logs I see NHibernate is trying to save a bar entity to the foo table. While I suspect it's my mappings it could be something else that I am simply overlooking. Code that creates the session factory (note I've also tried separate calls into .Mappings): Fluently.Configure().Database(MsSqlConfiguration.MsSql2008 .ConnectionString(c => c .Server(@"localhost\SQLEXPRESS") .Database("foo") .Username("foo") .Password("foo"))) .Mappings(m => { m.FluentMappings.AddFromAssemblyOf<FooMap>() .Conventions.Add(FluentNHibernate.Conventions.Helpers .Table.Is(x => "foos")); m.FluentMappings.AddFromAssemblyOf<BarMap>() .Conventions.Add(FluentNHibernate.Conventions.Helpers .Table.Is(x => "bars")); }) .BuildSessionFactory(); Unit test snippet: using (var session = Data.SessionHelper.SessionFactory.OpenSession()) { var bar = new Bar(); session.Save(bar); Assert.NotNull(bar.Id); }

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  • Calling NSFetchedResultsController & CoreData experts

    - by JK
    I am having a few nagging issues with NSFetchedResultsController and CoreData, any of which I would be very grateful to get help on. Issue 1 - Updates: I update my store on a background thread which results in certain rows being delete, inserted or updated. The changes are merged into the context on the main thread using the "mergeChangesFromContextDidSaveNotification:" method. Inserts and deletes are updated properly, but updates are not (e.g. the cell label is not updated with the change) although I have confirmed the updates to come through the contextDidSaveNotifcation, exactly like the inserts and deleted. My current workaround is to temporarily change the staleness interval of the context to 0, but this does not seem like the ideal solution. Issue 2 - Deleting objects: My fetch batch size is 20. If an object is deleted by the background thread which is in the first 20 rows, everything works fine. But if the object is after the first 20 rows and the table is scrolled down, a "CoreData could not fulfill a fault" error is raised. I have tried resaving the context and reperforming the frc fetch - all to no avail. Note: In this scenario, the frc delegate method "didChangeObject...." is not called for the delete - I assume this is because the object in question had not been faulted at that time (as it is was outside the initial fetch range). But for some reason, the context still thinks the object is around, although is has been deleted from the store. Issue 3 - Deleting sections : When the deletion of a row leads to the deletion of a section, I have gotten the "invalid number of rows in section???" error. I have worked around this by removing the "reloadSection" line from the NSFetchedResultsChangeMove: section and replacing it with "[tableView insertRowsAtIndexPaths...." This seems to work, but once again, I am not sure if this is the best solution. Any help would be greatly appreciated. Thank you!

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  • using asp.net membership provider in a dll

    - by Keith Barrows
    I've used Membership Providers in web apps over the last several years. I now have a new "request" for an internal project at work. They would like a service (not a web service) to do a quick authenticate against. Basically, exposing the ValidateUser(UserName, Password) method... I am building this in a DLL that will sit with our internal web site. What is the best approach to make this work? The DLL will not reference the web app and the web app will reference the DLL. How do I make the DLL aware of the Membership Provider? TIA PS: If this has been answered elsewhere please direct me to that... EDIT: I found an article on using ASP.NET Membership with WinForms and/or WPF applications. Unfortunately, these depend on an app.config file. A DLL appears to not use the app.config once published. If I am wrong, please set me straight! The article is here: http://aspalliance.com/1595_Client_Application_Services__Part_1.all

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  • How do I save the edits for a checkbox that implements an email notification?

    - by Ralph The Mouf
    On my site, a user gets email notifications when someone comments on their profile, or comments on their blog etc...I have made a email settings page that has checkboxes to allow the user to decide to receive emails or not. This is what I am wrapping around the email notification code chunck for the pages that have the php mail: <?php if(isset($_POST['email_toggle']) && $_POST['email_toggle'] == 'true') { if(isset($_POST['commentProfileSubmit']) && $auth) { $query etc $to = etc } } My question is what do I put on the email settings script that has the actual check boxes to make them stay checked or unchecked once you submit your settings? Another words what do I put in the if(isset portion to implement the changes? if(isset($_POST['email_toggle']) && $_POST['email_toggle'] == 'true') { /* what do I put here? */ header("Location: Profile.php?id=" . $auth->id); mysql_query($query,$connection); /* input/check boxes and submit button */ <tr> <td class="email_check"> <input type="checkbox" name="email_toggle" value="true" checked="checked" /> Receive email Notifications When Someone Answers A Question You've Answered </td> </tr> <tr> <td> <input style="margin:10px 0px 0px 10px;" class="submit" type="submit" name="email_toggle" value="Save Settings" /> </td> </tr> }

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  • Two Objects created with the same Address in Flex

    - by James
    Hi, I have an issue in flex which is causing a bit of a headache! I am adding objects to an ArrayCollection but in doing so, another ArrayCollection is also picking up these changes even though there is no binding occurring. I can see from the debug that the two ACs have the same address but for the life of me can't figure out why. I have two Array Collections: model.index.rows //The main array collection model.index.holdRows //The array collection that imitates the above This phantom data binding occurs only for the first iteration in the loop and for all others it will just write it the once. The reason this is proving troublesome is that it creates duplicate entries in my datagrid. public override function handleMessage(message:IMessage):void { super.handleMessage(message); if (message is IndexResponse) { var response:IndexResponse = message as IndexResponse; model.index.rows.removeAll(); model.index.indexIsEmpty = response.nullIndex; if (model.index.indexIsEmpty !== true) { //Update the index model from the response. Note: each property of the row object will be shown in the UI as a column in the grid response.index.forEach(function(entry:EntryData, i:int, a:Array):void { var row:Object = { fileID: entry.fileID, dadName: entry.dadName }; entry.tags.forEach(function(tag:Tag, i:int, a:Array):void { row[tag.name] = tag.value; }); model.index.rows.addItem(row); }); if(model.index.indexForNetworkView == true){ model.index.holdRows.source = model.index.holdRows.source.concat(model.index.rows.source); model.index.indexCounter++; model.index.indexForNetworkView = false; controller.indexController.showNetwork(model.index.indexCounter); } model.index.rows.refresh(); controller.networkController.show(); } } Has anyone else who has encountered something simillar propose a solution?

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  • Visual Studio 2010 compile error with std::string?

    - by AJG85
    So this is possibly the strangest thing I've seen recently and was curious how this could happen. The compiler gave me an error saying that std::string is undefined when used as a return type but not when used as a parameter in methods of a class! #pragma once #include <string> #include <vector> // forward declarations class CLocalReference; class CResultSetHandle; class MyClass { public: MyClass() {} ~MyClass {} void Retrieve(const CLocalReference& id, CResultSetHandle& rsh, std::string& item); // this is fine const std::string Retrieve(const CLocalReference& id, CResultSetHandle& rsh); // this fails with std::string is undefined?!?! }; Doing a Rebuild All it still happened I had to choose clean solution and then Rebuild All again after for the universe to realign. While it's resolved for the moment I'd still like to know what could have caused this because I'm at a loss as to why when there should be no conflicts especially when I always use fully qualified names for STL.

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  • Memory usage does not drop -- no leaks though

    - by climbon
    I have UINavigationController controlling several views. One of the views is composed of 20 scrollable pages. Each page is a constructed on the fly from UIViews by adding buttons, labels, UIImageViews etc. When this UIView is popped off the stack, the memory usage remains the same. Hence it keeps rising if I keep pushing/popping that view. In my dealloc, I am traversing through all 20 pages and finding each type of object which got added via addSubview and then do a release on it but instruments says my memory usage never goes down! I am trying to use 'retainCount' to see what is up with objects I am releasing but I am perhaps not getting true picture via retainCount. For some elements retainCount shows 2 so I try to release that object twice but then app crashes. If I release it once it works but memory usage never go down :( Q1: Do I need to traverse find each element and then do a release on that element ? Why can't I release a parent object and all objects contained by it would get released automatically ? Q2: Is retainCount a reliable indicator ?

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  • Localisable Resources: how can (should one?!) wrap a UI layer source as a BL layer service?

    - by Ciel
    A service that returns localised strings could be wrapped in a service, so that it could be used both locally (eg in an MVC app) and remotely (eg possibly Silverlight). But...if sticking with the standard practice of creating resources in the UI assembly, that would in effect make a lower layer (BL/Services) have to have a ref on a higher layer (UI)...a definite no-no. And whereas a lot of AppWide resources (eg: AppName, OK, Cancel, etc.) could be defined in a Common cross-cutting assembly, and the BL/ResourceSerouce could ref and wrap those, that doesn't work in a a Modular App, where the Core app should have no binding to/knowledge of any Module. One solution could be to have each module, once mounted in mem, 'register' their Resource files with the service, who would then return it to the service (rather a long round trip, but at least consistent as a service, and potentially resources/images could be shared with other resources). Secondly, that may work in a web app...but not sure how that pattern could be extended to a Silverlight modular app (the round tripping becomes prohibitive). ie...what are best practices for allowing Resources to be to be defined by the UI designer, in a higher level, but served from the lower BL layer, as a Service? Or is there a better way of understanding/solving the problem?

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  • Use of properties vs backing-field inside owner class

    - by whatispunk
    I love auto-implemented properties in C# but lately there's been this elephant standing in my cubicle and I don't know what to do with him. If I use auto-implemented properties (hereafter "aip") then I no longer have a private backing field to use internally. This is fine because the aip has no side-effects. But what if later on I need to add some extra processing in the get or set? Now I need to create a backing-field so I can expand my getters and setters. This is fine for external code using the class, because they won't notice the difference. But now all of the internal references to the aip are going to invoke these side-effects when they access the property. Now all internal access to the once aip must be refactored to use the backing-field. So my question is, what do most of you do? Do you use auto-implemented properties or do you prefer to always use a backing-field? What do you think about properties with side-effects?

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  • jQuery: If user clicks out of div

    - by Paul Knopf
    I am creating a popup in query. All is well with the popup on hover. I made it see a timer starts when user's mouse leaves the div to close it. If he enters the div again before the timer is done, then the timer is cleared. This is fine, but what if a user clicks out of the div? I want that to also close the div. The only problem is that I don't want to attach click events to the wrapper on the page (because it includes the popout menu). I have seen techniques that wraps entire screen with a transparent div, and then attach a click event to hit. Although this may work, it confuses the user if he clicks the hidden div intending to click a link. He will have to click the link twice. Once two close the div (hiding the link), and another time to actually click think. Also, you loose in mouse cursors attached to any masked elements on the page (such as links cursor pointer, etc). There has to be a way to check if the user clicked out of the div without a modal and without attaching events to the entire page (page wrappers and child elements included). onclicksomewhereelse="closeme();" lol.

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  • The best way to write a jQuery plugin - If there is such a way?

    - by Nick Lowman
    There are quite a few ways to write plugins i.e. here's a nice example and what I've seen quite a lot of lately is the following code pattern and it's used by Doug Neiner here; (function($){ $.formatLink = function(el, options){ var base = this; base.$el = $(el); base.el = el; base.$el.data("formatLink", base); base.init = function(){ base.options = $.extend({}, $.formatLink.defaultOptions, options); //code here } base.init(); }; $.formatLink.defaultOptions = { }; $.fn.formatLink = function(options){ return this.each(function(){ (new $.formatLink(this, options)); }); }; })(jQuery); So, can anyone tell me the benefits of using the pattern above rather than the one below. I can't see the point in calling the $.extend function for every element in the jQuery stack (above), where the example below only does this once and then works on the stack. To test it I created two plugins, using both patterns, which applied styles to about 5000 li elements and the code below took about 1 second whereas the pattern above took about 1.3 seconds. (function($){ $.fn.formatLink = function(options){ var options = $.extend({}, $.fn.formatLink.defaultOptions, options || {}); return this.each(function(){ //code here }); }); $.fn.formatLink.defaultOptions ={} })(jQuery);

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  • My list item's child label elements disappear in IE on accordion menu opening

    - by Scott B
    I've got an app that's working pretty flawlessly in Chrome and FF, however, when I view it in IE, all is well until I click on a header element to activate it (jQuery accordion). What happens then is that I see a brief flash where the content is there, then suddenly the entire left column disappears. This column is generated by a floated label element with a class of ".left" as seen below... <ul class="menu collapsible"> <li class='expand sectionTitle'><a href='#'>General Settings</a> <ul class='acitem'> <li class="section"> <label class="left">This item if floated left with a defined width of 190px via css. This is the item that's disappearing after a brief display</label> <input class="input" value="input element here" /> <label class="description">This element has a margin-left:212px; set via css in order to be positioned to the right of the label element as if in an adjacent table cell. When I add a max-width property to this element, it disappears in IE too!</label> </li> </ul> </li> </ul> As you can see from the comments in the code above (for the two label elements) the description label disappears once I set a max-width on it (I don't have a max-width on the left label element, but it disappears nonetheless). The initial view of this UL menu is fine (note the expand class declaration which makes this part of the accordion open at startup. Its not until I click the "General Settings" to toggle it closed, then back open, that the left class elements disappear (and only in IE)

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  • In Rails, how would I include a section of a page only if the rest of the page doesn't match a certain regexp?

    - by Simon
    We have a site with a lot of user-generated content, and we'd like to show Google ads on it. Some of the content is such that we mustn't show the ads on pages containing that content, or else the whole site gets banned. We've come up with a regexp which we think will match all the offending content. So, three approaches come to mind: Render the page once without the ad section, and then insert the ad section into it if it's clean Render the page as normal, and do the insertion in client-side javascript Render the page above the ad section, capturing only the parts of the page that change; make sure there are no changing parts afterwards. Only show the ads if the captured text is clean, and make sure the unchanging, uncaptured parts are well-vetted in advance. The first one seems like it might delay the page rendering for too long; the second seems like it might delay showing the ads too long; and the third seems too fragile. Is there a better approach? If not, which one is the best solution of the three?

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  • Rationale of C# iterators design (comparing to C++)

    - by macias
    I found similar topic: http://stackoverflow.com/questions/56347/iterators-in-c-stl-vs-java-is-there-a-conceptual-difference Which basically deals with Java iterator (which is similar to C#) being unable to going backward. So here I would like to focus on limits -- in C++ iterator does not know its limit, you have by yourself compare the given iterator with the limit. In C# iterator knows more -- you can tell without comparing to any external reference, if the iterator is valid or not. I prefer C++ way, because once having iterator you can set any iterator as a limit. In other words if you would like to get only few elements instead of entire collection, you don't have to alter the iterator (in C++). For me it is more "pure" (clear). But of course MS knew this and C++ while designing C#. So what are the advantages of C# way? Which approach is more powerful (which leads to more elegant functions based on iterators). What do I miss? If you have thoughts on C# vs. C++ iterators design other than their limits (boundaries), please also answer. Note: (just in case) please, keep the discussion strictly technical. No C++/C# flamewar.

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  • How do I avoid a race condition in my Rails app?

    - by Cathal
    Hi, I have a really simple Rails application that allows users to register their attendance on a set of courses. The ActiveRecord models are as follows: class Course < ActiveRecord::Base has_many :scheduled_runs ... end class ScheduledRun < ActiveRecord::Base belongs_to :course has_many :attendances has_many :attendees, :through => :attendances ... end class Attendance < ActiveRecord::Base belongs_to :user belongs_to :scheduled_run, :counter_cache => true ... end class User < ActiveRecord::Base has_many :attendances has_many :registered_courses, :through => :attendances, :source => :scheduled_run end A ScheduledRun instance has a finite number of places available, and once the limit is reached, no more attendances can be accepted. def full? attendances_count == capacity end attendances_count is a counter cache column holding the number of attendance associations created for a particular ScheduledRun record. My problem is that I don't fully know the correct way to ensure that a race condition doesn't occur when 1 or more people attempt to register for the last available place on a course at the same time. My Attendance controller looks like this: class AttendancesController < ApplicationController before_filter :load_scheduled_run before_filter :load_user, :only => :create def new @user = User.new end def create unless @user.valid? render :action => 'new' end @attendance = @user.attendances.build(:scheduled_run_id => params[:scheduled_run_id]) if @attendance.save flash[:notice] = "Successfully created attendance." redirect_to root_url else render :action => 'new' end end protected def load_scheduled_run @run = ScheduledRun.find(params[:scheduled_run_id]) end def load_user @user = User.create_new_or_load_existing(params[:user]) end end As you can see, it doesn't take into account where the ScheduledRun instance has already reached capacity. Any help on this would be greatly appreciated.

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  • Help me find article on Multi-threading and Event Handling in Java

    - by JDR
    I once read an article on how to properly write event handlers for multi-threading in Java, but I can't for the life of me find it anymore. It described the pitfalls and potentials for deadlocks that can occur when firing events (not Swing events mind you, but general events like model update notifications). To clarify, the situation would be as such: // let's say this is code from an MVC model somewhere public void setSomeProperty(String myProperty){ if(!this.myProperty.equals(myProperty)){ this.myProperty = myProperty; fireMyPropertyChangedEvent(...); } } The article described how passing control to arbitrary external listener code was a potential cause for deadlock. I now find myself in a situation where I need to fire such events in a multithreaded environment and I would very much like to read the article again to see what it has to say before I continue. Does anyone know the article I'm referring to? I believe it came as a (fairly short) PDF. It started off with an initial naive implementation and incrementally pointed out flaws and improved upon it. It ended with a sort of final proper-way-to-fire-multithreaded-events. I've searched endlessly in my browse history and on google, but all I could find were endless amounts topics on Swing event dispatch threads. Thank you.

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  • optimistic and pessimistic locks

    - by billmce
    Working on my first php/Codeigniter project and I’ve scoured the ‘net for information on locking access to editing data and haven’t found very much information. I expect it to be a fairly regular occurrence for 2 users to attempt to edit the same form simultaneously. My experience (in the stateful world of BBx, filePro, and other RAD apps) is that the data being edited is locked using a pessimistic lock—one user has access to the edit form at the time. The second user basically has to wait for the first to finish. I understand this can be done using Ajax sending XMLHttpRequests to maintain a ‘lock’ database. The php world, lacking state, seems to prefer optimistic locking. If I understand it correctly it works like this: both users get to access the data and they each record a ‘before changes’ version of the data. Before saving their changes, the data is once again retrieved and compared the ‘before changes’ version. If the two versions are identical then the users changes are written. If they are different; the user is shown what has changed since he/she started editing and some mechanism is added to resolve the differences—or the user is shown a ‘Sorry, try again’ message. I’m interested in any experience people here have had with implementing both pessimistic and optimistic locking. If there are any libraries, tools, or ‘how-to’s available I’m appreciate a link. Thanks

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  • What should I use to increase performance. View/Query/Temporary Table

    - by Shantanu Gupta
    I want to know the performance of using Views, Temp Tables and Direct Queries Usage in a Stored Procedure. I have a table that gets created every time when a trigger gets fired. I know this trigger will be fired very rare and only once at the time of setup. Now I have to use that created table from triggers at many places for fetching data and I confirms it that no one make any changes in that table. i.e ReadOnly Table. I have to use this tables data along with multiple tables to join and fetch result for further queries say select * from triggertable By Using temp table select ... into #tx from triggertable join t2 join t3 and so on select a,b, c from #tx --do something select d,e,f from #tx ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. By Using Views create view viewname ( select ... from triggertable join t2 join t3 and so on ) select a,b, c from viewname --do something select d,e,f from viewname ---do somethign --and so on --around 6-7 queries in a row in a stored procedure. This View can be used in other places as well. So I will be creating at database rather than at sp By Using Direct Query select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something select a,b, c from select ... into #tx from triggertable join t2 join t3 join ... --do something . . --and so on --around 6-7 queries in a row in a stored procedure. Now I can create a view/temporary table/ directly query usage in all upcoming queries. What would be the best to use in this case.

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  • Callers block until getFoo() has a value ready?

    - by Sean Owen
    I have a Java Thread which exposes a property which other threads want to access: class MyThread extends Thread { private Foo foo; ... Foo getFoo() { return foo; } ... public void run() { ... foo = makeTheFoo(); ... } } The problem is that it takes some short time from the time this runs until foo is available. Callers may call getFoo() before this and get a null. I'd rather they simply block, wait, and get the value once initialization has occurred. (foo is never changed afterwards.) It will be a matter of milliseconds until it's ready, so I'm comfortable with this approach. Now, I can make this happen with wait() and notifyAll() and there's a 95% chance I'll do it right. But I'm wondering how you all would do it; is there a primitive in java.util.concurrent that would do this, that I've missed? Or, how would you structure it? Yes, make foo volatile. Yes, synchronize on an internal lock Object and put the check in a while loop until it's not null. Am I missing anything?

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  • mootools event listener disappears after element.innerHTML is changed

    - by baiano
    I putting together a page that will display a set of stored values. I am using mootools and AJAX calls to update the values without needing to refresh the page each time the user selects a new item from the drop down menus. the HTML each line looks something like: <div class="selections"> <input class="checkbox selector" type="checkbox" CHECKED /> <span class="b_name"> <select class="b_n selector"> <!-- options --> </select> </span> <span class="b_level"> <select class="b_l selector"> <!-- options --> </select> </span> <span class="values"> <!-- the values --> </span> In the head I have set up an event listener like: $$('.selector').addEvent('change', function(event){changeValues(this);}); My problem is that when the "b_name" select changes I have to update the list of options in the "b_level" select. I accomplish that by getting a list of the possible options from my database through a php script on another page and replacing "b_level"'s innerHTML. Once I do that, the event listener attached to "b_l selector" no longer works. I tried to resolve this issue by explicitly attaching an event listener to "b_l selector" each time "b_name" changes like so: row.getElement('.b_l').addEvent('change', function(event){changeValues(row.getElement('.b_l'));}); where 'row' is the html element 'div.selections'. It still isn't working and I have no idea what's going on. Can anyone offer a suggestion as to how I can get this resolved? or perhaps a better way to do what I'm doing. Thanks

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  • Is Subversion's 'Lazy Copy' still lazy when overwriting a previously deleted file?

    - by JW
    Is Subversion's 'Lazy Copy' still lazy when overwriting a previously deleted file? I store my externals in a separate folder for each version: i.e say for dojo I'd have: webroot\ scripts\ dojo-v-1.0.0\ dojo-v-1.1.0\ etc. By doing this, for me at least, I feel it makes it easier to switch over to a new version. By only adding each new version i am not really giving svn the history it needs to do lazy copies. So one tactic I have used is to svn copy over the old version over to where the new one will be then svn delete that whole folder then unpack my newer version into that place then svn add them The idea is to avoid having a massive amount of duplicated data in my repo. I hope svn is looking at the new files and saying, "hey, i already had this once, copied, then deleted...so i am only going to be lazy store the changes". That was my theory - but does that happen in practice? p.s. Yes I know an alternative is to set the 'externals properties on the folder' - but that's another question.

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  • entity framework navigation property further filter without loading into memory

    - by cellik
    Hi, I've two entities with 1 to N relation in between. Let's say Books and Pages. Book has a navigation property as Pages. Book has BookId as an identifier and Page has an auto generated id and a scalar property named PageNo. LazyLoading is set to true. I've generated this using VS2010 & .net 4.0 and created a database from that. In the partial class of Book, I need a GetPage function like below public Page GetPage(int PageNumber) { //checking whether it exist etc are not included for simplicity return Pages.Where(p=>p.PageNo==PageNumber).First(); } This works. However, since Pages property in the Book is an EntityCollection it has to load all Pages of a book in memory in order to get the one page (this slows down the app when this function is hit for the first time for a given book). i.e. Framework does not merge the queries and run them at once. It loads the Pages in memory and then uses LINQ to objects to do the second part To overcome this I've changed the code as follows public Page GetPage(int PageNumber) { MyContainer container = new MyContainer(); return container.Pages.Where(p=>p.PageNo==PageNumber && p.Book.BookId==BookId).First(); } This works considerably faster however it doesn't take into account the pages that have not been serialized to the db. So, both options has its cons. Is there any trick in the framework to overcome this situation. This must be a common scenario where you don't want all of the objects of a Navigation property loaded in memory when you don't need them.

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  • When is it safe to use a broken hash function?

    - by The Rook
    It is trivial to use a secure hash function like SHA256 and continuing to use md5 is reckless behavior. However, there are some complexities to hash function vulnerabilities that I would like to better understand. Collisions have been generated for md4 and md5. According to NIST md5() is not a secure hash function. It only takes 2^39th operations to generate a collision and should never be used for passwords. However SHA1 is vulnerable to a similar collision attack in which a collision can be found in 2^69 operations, where as brute force is 2^80th. No one has generated a sha1 collision and NIST still lists sha1 as a secure message digest function. So when is it safe to use a broken hash function? Even though a function is broken it can still be "big enough". According to Schneier a hash function vulnerable to a collsion attack can still be used as an HMAC. I believe this is because the security of an HMAC is Dependant on its secret key and a collision cannot be found until this key is obtained. Once you have the key used in a HMAC its already broken, so its a moot point. What hash function vulnerabilities would undermine the security of an HMAC? Lets take this property a bit further. Does it then become safe to use a very weak message digest like md4 for passwords if a salt is perpended to the password? Keep in mind the md4 and md5 attacks are prefixing attacks, and if a salt is perpended then an attacker cannot control the prefix of the message. If the salt is truly a secret, and isn't known to the attacker, then does it matter if its a appended to the end of the password? Is it safe to assume that an attacker cannot generate a collision until the entire message has been obtained? Do you know of other cases where a broken hash function can be used in a security context without introducing a vulnerability? (Please post supporting evidence because it is awesome!)

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  • When is it possible to override top-level bindings in (R7RS) scheme?

    - by Marc
    I have read the current draft of the forthcoming R7RS scheme standard (small language), but I don't understand under which conditions it is not an error to redefine top-level bindings. I guess that it is possible to define or set! a binding that has been introduced at the top-level of a program a second time. But what about imported bindings from an external library? Is it possible to override these bindings by the standard? On page 26/27 of the report, it says: The top level of a program may also include import declarations. In a library declaration, it is an error to import the same identifier more than once with different bindings, or to redefine or mutate an imported binding with define, define-syntax or set!. However, a REPL should permit these actions. Does it mean that redefining is only an error when it does happen in libraries for imported bindings? I understand that it prohibits optimisations by compilers if the compiler does not know whether, say + still means the built-in addition or is any other user-specified error. But from this perspective, it does not make sense to restrict forbidding to rebind on the library level, when it would also make sense (at least) for imported bindings in programs. P.S.: As this is all about the environment of a scheme program: am I right in saying that environments are not first class citizens because one cannot get hold of the current environment? (Which, in turn, allows a compiled program to forget about the chosen names of the bindings.)

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  • Understanding REST through an example

    - by grifaton
    My only real exposure to the ideas of REST has been through Ruby on Rails' RESTful routing. This has suited me well for the kind of CRUD-based applications I have built with Rails, but consequently my understanding of RESTfulness is somewhat limited. Let's say we have a finite collection of Items, each of which has a unique ID, and a number of properties, such as colour, shape, and size (which might be undefined for some Items). Items can be used by a client for a period of time, but each Item can only be used by one client at once. Access to Items is regulated by a server. Clients can request the temporary use of certain items from a server. Usually, clients will only be interested in getting access to a number of Items with particular properties, rather than getting access to specific Items. When a client requests use of a number of Items, the server responds with a list of IDs corresponding to the request, or with a response that says that the requested Items are not currently available or do not exist. A client can make the following kinds of request: Tell me how many green triangle Items there are (in total/available). Give me use of 200 large red Items. I have finished with Items 21, 23, 23. Add 100 new red square Items. Delete 50 small green Items. Modify all big yellow pentagon Items to be blue. The toy example above is like a resource allocation problem I have had to deal with recently. How should I go about thinking about it RESTfully?

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