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• What is the best database structure for this scenario?

  - by Ricketts

  I have a database that is holding real estate MLS (Multiple Listing Service) data. Currently, I have a single table that holds all the listing attributes (price, address, sqft, etc.). There are several different property types (residential, commercial, rental, income, land, etc.) and each property type share a majority of the attributes, but there are a few that are unique to that property type. My question is the shared attributes are in excess of 250 fields and this seems like too many fields to have in a single table. My thought is I could break them out into an EAV (Entity-Attribute-Value) format, but I've read many bad things about that and it would make running queries a real pain as any of the 250 fields could be searched on. If I were to go that route, I'd literally have to pull all the data out of the EAV table, grouped by listing id, merge it on the application side, then run my query against the in memory object collection. This also does not seem very efficient. I am looking for some ideas or recommendations on which way to proceed. Perhaps the 250+ field table is the only way to proceed. Just as a note, I'm using SQL Server 2012, .NET 4.5 w/ Entity Framework 5, C# and data is passed to asp.net web application via WCF service. Thanks in advance.

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• Is a "factory" method the right pattern?

  - by jdt141

  Hey all - So I'm working to improve an existing implementation. I have a number of polymorphic classes that are all composed into a higher level container class. The problem I'm dealing with at the moment is that the higher level container class, well, sucks. It looks something like this, which I really don't have a problem with (as the polymorphic classes in the container should be public). My real issue is the constructor... /* * class1 and class 2 derive from the same superclass */ class Container { public: boost::shared_ptr<ComposedClass1> class1; boost::shared_ptr<ComposedClass2> class2; private: ... } /* * Constructor - builds the objects that we need in this container. */ Container::Container(some params) { class1.reset(new ComposedClass1(...)); class2.reset(new ComposedClass2(...)); } What I really need is to make this container class more re-usable. By hard-coding up the member objects and instantiating them, it basically isn't and can only be used once. A factory is one way to build what I need (potentially by supplying a list of objects and their specific types to be created?) Other ways to get around this problem? Seems like someone should have solved it before... Thanks!

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• VB.net httpwebrequest For loop hangs every 10 or so iterations

  - by user574632

  Hello, I am trying to loop through an array and perform an httpwebrequest in each iteration. The code seems to work, however it pauses for a while (eg alot longer than the set timeout. Tried setting that to 100 to check and it still pauses) after every 10 or so iterations, then carries on working. Here is what i have so far: For i As Integer = 0 To numberOfProxies - 1 Try 'create request to a proxyJudge php page using proxy Dim request As HttpWebRequest = HttpWebRequest.Create("http://www.pr0.net/deny/azenv.php") request.Proxy = New Net.WebProxy(proxies(i)) 'select the current proxie from the proxies array request.Timeout = 10000 'set timeout Dim response As HttpWebResponse = request.GetResponse() Dim sr As StreamReader = New StreamReader(response.GetResponseStream()) Dim pageSourceCode As String = sr.ReadToEnd() 'check the downloaded source for certain phrases, each identifies a type of proxy 'HTTP_X_FORWARDED_FOR identifies a transparent proxy If pageSourceCode.Contains("HTTP_X_FORWARDED_FOR") Then 'delegate method for cross thread safe UpdateListbox(ListBox3, proxies(i)) ElseIf pageSourceCode.Contains("HTTP_VIA") Then UpdateListbox(ListBox2, proxies(i)) Else UpdateListbox(ListBox1, proxies(i)) End If Catch ex As Exception 'MessageBox.Show(ex.ToString) used in testing UpdateListbox(ListBox4, proxies(i)) End Try completedProxyCheck += 1 lblTotalProxiesChecked.CustomInvoke(Sub(l) l.Text = completedProxyCheck) Next I have searched all over this site and via google, and most responses to this type of question say the response must be closed. I have tried a using block, eg: Using response As HttpWebResponse = request.GetResponse() Using sr As StreamReader = New StreamReader(response.GetResponseStream()) Dim pageSourceCode As String = sr.ReadToEnd() 'check the downloaded source for certain phrases, each identifies a type of proxy 'HTTP_X_FORWARDED_FOR identifies a transparent proxy If pageSourceCode.Contains("HTTP_X_FORWARDED_FOR") Then 'delegate method for cross thread safe UpdateListbox(ListBox3, proxies(i)) ElseIf pageSourceCode.Contains("HTTP_VIA") Then UpdateListbox(ListBox2, proxies(i)) Else UpdateListbox(ListBox1, proxies(i)) End If End Using End Using And it makes no difference (though i may have implemented it wrong) As you can tell im very new to VB or any OOP so its probably a simple problem but i cant work it out. Any suggestions or just tips on how to diagnose these types of problems would be really appreciated.

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• Java method keyword "final" and its use

  - by Lukas Eder

  When I create complex type hierarchies (several levels, several types per level), I like to use the final keyword on methods implementing some interface declaration. An example: interface Garble { int zork(); } interface Gnarf extends Garble { /** * This is the same as calling {@link #zblah(0)} */ int zblah(); int zblah(int defaultZblah); } And then abstract class AbstractGarble implements Garble { @Override public final int zork() { ... } } abstract class AbstractGnarf extends AbstractGarble implements Gnarf { // Here I absolutely want to fix the default behaviour of zblah // No Gnarf shouldn't be allowed to set 1 as the default, for instance @Override public final int zblah() { return zblah(0); } // This method is not implemented here, but in a subclass @Override public abstract int zblah(int defaultZblah); } I do this for several reasons: It helps me develop the type hierarchy. When I add a class to the hierarchy, it is very clear, what methods I have to implement, and what methods I may not override (in case I forgot the details about the hierarchy) I think overriding concrete stuff is bad according to design principles and patterns, such as the template method pattern. I don't want other developers or my users do it. So the final keyword works perfectly for me. My question is: Why is it used so rarely in the wild? Can you show me some examples / reasons where final (in a similar case to mine) would be very bad?

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• gried view problem asp.net

  - by kenom

  Why i get this error: The data types text and nvarchar are incompatible in the equal to operator. The field of "username" in database is text type... This is my soruce: <%@ Control Language="C#" AutoEventWireup="true" CodeFile="my_answers.ascx.cs" Inherits="kontrole_login_my_answers" %> <div style=" margin-top:-1280px; float:left;"> <p></p> <div id="question"> Add question </div> </div> <asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1" > </asp:GridView> <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:estudent_piooConnectionString %>" SelectCommand="SELECT * FROM [question] WHERE ([username] = @fafa)"> <SelectParameters> <asp:QueryStringParameter Name="fafa" QueryStringField="user" Type="String"/> </SelectParameters> </asp:SqlDataSource>

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• Bi-directional view model syncing with "live" collections and properties (MVVM)

  - by Schneider

  I am getting my knickers in a twist recently about View Models (VM). Just like this guy I have come to the conclusion that the collections I need to expose on my VM typically contain a different type to the collections exposed on my business objects. Hence there must be a bi-directional mapping or transformation between these two types. (Just to complicate things, on my project this data is "Live" such that as soon as you change a property it gets transmitted to other computers) I can just about cope with that concept, using a framework like Truss, although I suspect there will be a nasty surprise somewhere within. Not only must objects be transformed but a synchronization between these two collections is required. (Just to complicate things I can think of cases where the VM collection might be a subset or union of business object collections, not simply a 1:1 synchronization). I can see how to do a one-way "live" sync, using a replicating ObservableCollection or something like CLINQ. The problem then becomes: What is the best way to create/delete items? Bi-directinal sync does not seem to be on the cards - I have found no such examples, and the only class that supports anything remotely like that is the ListCollectionView. Would bi-directional sync even be a sensible way to add back into the business object collection? All the samples I have seen never seem to tackle anything this "complex". So my question is: How do you solve this? Is there some technique to update the model collections from the VM? What is the best general approach to this?

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• Copy vector of values to vector of pairs in one line

  - by Kirill V. Lyadvinsky

  I have the following types: struct X { int x; X( int val ) : x(val) {} }; struct X2 { int x2; X2() : x2() {} }; typedef std::pair<X, X2> pair_t; typedef std::vector<pair_t> pairs_vec_t; typedef std::vector<X> X_vec_t; I need to initialize instance of pairs_vec_t with values from X_vec_t. I use the following code and it works as expected: int main() { pairs_vec_t ps; X_vec_t xs; // this is not empty in the production code ps.reserve( xs.size() ); { // I want to change this block to one line code. struct get_pair { pair_t operator()( const X& value ) { return std::make_pair( value, X2() ); } }; std::transform( xs.begin(), xs.end(), back_inserter(ps), get_pair() ); } return 0; } What I'm trying to do is to reduce my copying block to one line with using boost::bind. This code is not working: for_each( xs.begin(), xs.end(), boost::bind( &pairs_vec_t::push_back, ps, boost::bind( &std::make_pair, _1, X2() ) ) ); I know why it is not working, but I want to know how to make it working without declaring extra functions and structs?

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• How do I format the contents of a DataGrid cell as a Date? as Currency?

  - by Ben McCormack

  I have a Silverlight DataGrid that's being populated with different types of data for each column. I'm trying to figure out how to format some of the contents of the DataGrid's cells, specifically for dates and formatting. I have a date column that's currently displaying like: 3/11/2010 12:00:00 AM. I would rather it display like 3/14/2010. I have a number column that's currently displaying like: 51.32. I'd rather it display as currency like $51.32. I'm not sure how I can go about doing this. I'd prefer to do it in XAML instead of C#, but both solutions are fine. For reference, here's my XAML so far: </data:DataGridTextColumn> <data:DataGridTextColumn Header="Payee" Binding="{Binding Payee}"/> <data:DataGridTextColumn Header="Category" Binding="{Binding Category}"/> <data:DataGridTextColumn Header="Memo" Binding="{Binding Memo}"/> <data:DataGridTextColumn Header="Inflow" Binding="{Binding Inflow}"/> <data:DataGridTextColumn Header="Outflow" Binding="{Binding Outflow}"/> </data:DataGrid.Columns>

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• How do I place another attribute to a MKAnnotation?

  - by kevin Mendoza

  for my app each annotation on a map corresponds to a mine locality. each mine has its own unique 7 digit integer identifier. I'm trying to add the property minesEntryNumber to the annotation so when the annotation is clicked on later I can bring up specific information on the selected annotation. This is part of my code: for (id mine in mines) { //NSLog(@"in the loop"); workingCoordinate.latitude = [[mine latitudeInitial] doubleValue]; workingCoordinate.longitude = [[mine longitudeInitial] doubleValue]; iProspectAnnotation *tempMine = [[iProspectAnnotation alloc] initWithCoordinate:workingCoordinate]; [tempMine setTitle:[mine mineName]]; tempMine.minesEntryNumber = [mine entryNumber]; //other code for dealing with mine types and adding the annotation to the mapview } the code works fine without the "tempMine.minesEntryNumber = [mine entryNumber];" part. It loads the map and shows the annotations. however when I try and put this in it brings up an error. So how do I add this property to each annotation and how do I access it later in a different .m file?

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• Gradle fails injecting dependencies into subprojects using fileTree

  - by Matthias

  Maybe I'm missing something about the way Gradle works. What I have here is a parent project, which only contains configuration, i.e. there won't be any artifact being built when building it, it merely manages and builds all its subprojects. Now the subprojects share some dependency configuration, so I figured what I would do in the root project's build.gradle is: subprojects { dependencies { compile fileTree(dir: 'lib', includes: ['*.jar']) } } that, however, does not work, it fails with a rather obscure error message: A problem occurred evaluating root project 'qype-android' Cause: No signature of method: org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.compile() is applicable for argument types: (org.gradle.api.internal.file.DefaultConfigurableFileTree) values: [file set 'lib'] Possible solutions: module(java.lang.Object) after some trial and error, I could "fix" this issue by applying the 'java' plugin to the parent project. How come? I don't see anywhere from the Gradle docs that a fileTree dependency requires the Java plugin. Even so, why would I need it on the project that is injecting the configuration, as opposed to on the project that is being configured (note that the subprojects all apply the Java plugin themselves)? Does this mean that if I have N different subprojects that are all of varying natures, and apply different plugins, that the parent projects must always apply the set of all plugins beings used somewhere to itself, too?

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• Simply if Statement for checking co-ordinate square.

  - by JonB

  I have an UIImageView and taking the raw touch input. I need to check if a touch is within a certain set of squares. At the moment... I have this if statement.... if(46 < touchedAt.x && touchedAt.x < 124 && 18 < touchedAt.y && touchedAt.y < 75) but I have tried to simplify it to this one... if(46 < touchedAt.x < 124 && 18 < touchedAt.y < 75) It didn't work. Is it possible to simplify like this or am I stuck with the slightly lengthier version at the top? Is there a reason why the types of comparisons in the bottom if don't work? Many Thanks.

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• Strategy for WCF server with .Net clients and Android clients?

  - by D.H.

  I am using WCF to write a server that should be able to communicate with .Net clients, Android clients and possibly other types of clients. The main type of client is a desktop application that will be written in .Net. This client will usually be on the same intranet as the server. It will make an initial call to the server to get the current state of the system and will then receive updates from the server whenever a value changes. These updates are frequent, perhaps once a second. The Android clients will connect over the Internet. This client is also interested in updates, but it is not as critical as for the desktop client so a (less frequent) polling scenario might be acceptable. All clients will have to login to use the services, and when connecting over the Internet the connection should be secure. I am familiar with WCF but I am not sure what bindings are most appropriate for the scenario and what security solution to use. Also, I have not used Android, but I would like to make it as simple as possible for the person implementing the Android client to consume my services. So, what is my strategy?

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• Multiple threads modifying a collection in Java??

  - by posdef

  Hi, The project I am working on requires a whole bunch of queries towards a database. In principle there are two types of queries I am using: read from excel file, check for a couple of parameters and do a query for hits in the database. These hits are then registered as a series of custom classes. Any hit may (and most likely will) occur more than once so this part of the code checks and updates the occurrence in a custom list implementation that extends ArrayList. for each hit found, do a detail query and parse the output, so that the classes created in (I) get detailed info. I figured I would use multiple threads to optimize time-wise. However I can't really come up with a good way to solve the problem that occurs with the collection these items are stored in. To elaborate a little bit; throughout the execution objects are supposed to be modified by both (I) and (II). I deliberately didn't c/p any code, as it would be big chunks of code to make any sense.. I hope it make some sense with the description above. Thanks,

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• Strangely structured xml code finding last value of a certain type using java

  - by Damien.Bell

  Thus the structure is something like this: OasisReportMessagePayloadRTOReport_ItemReport_Data Under report data it's broken into categories: >>Zone >>Type >>Value >>Interval What I need to do is: Get the value if the type is equal to 'myType' and the interval value is the LARGEST. So an example of the xml might be (under report_data): OasisReport MessagePayload RTO REPORT_ITEM REPORT_DATA <zone>myZone1</zone> -- This should be the same in all reports since I only get them for 1 zone <type>myType</type> --This can change from line to line <value>12345</value>--This changes every interval <Interval>122</Interval> -- This is essentially how many 5 minute intervals have taken place since the beginning of a day, finding the "max" lets me know it's the newest data. Thereby I want to find stuff of "MyType" for the "max" interval and pull the Value (into a string, or a double, if not I can convert from string. Can someone help me with this task? Thanks! Note: I've used Xpath to handle things like this in the past, but it seems outlandish for this... as it's SO complex (since not all the reports live in the same report_item, and not all the types are the same in each report)

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• OpenGL particle system

  - by allan

  I'm really new with OpenGL, so bear with me. I'm trying to simulate a particle system using OpenGl but I can't get it to work, this is what I have so far: #include <GL/glut.h> int main (int argc, char **argv){ // data allocation, various non opengl stuff ............ glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE ); glutInitWindowPosition(100,100); glutInitWindowSize(size, size); glPointSize (4); glutCreateWindow("test gl"); ............ // initial state, not opengl ............ glViewport(0,0,size,size); glutDisplayFunc(display); glutIdleFunc(compute); glutMainLoop(); } void compute (void) { // change state not opengl glutPostRedisplay(); } void display (void) { glClear(GL_COLOR_BUFFER_BIT); glBegin(GL_POINTS); for(i = 0; i<nparticles; i++) { // two types of particles if (TYPE(particle[i]) == 1) glColor3f(1,0,0); else glColor3f(0,0,1); glVertex2f(X(particle[i]),Y(particle[i])); } glEnd(); glFlush(); glutSwapBuffers(); } I get a black window after a couple of seconds (the window has just the title bar before that). Where do I go wrong? Any help would be very much appreciated. Thanks. LE: the x and y coordinates of each particle are within the interval (0,size)

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• MVC: model of type Nullable<T>

  - by Fyodor Soikin

  I have a partial view that inherits from ViewUserControl<Guid?> - i.e. it's model is of type Nullable<Guid>. Very simple view, nothing special, but that's not the point. Somewhere else, I do Html.RenderPartial( "MyView", someGuid ), where someGuid is of type Nullable<Guid>. Everything's perfectly legal, should work OK, right? But here's the gotcha: the second argument of Html.RenderPartial is of type object, and therefore, Nullable<Guid> being a value type, it must be boxed. But nullable types are somehow special in the CLR, so that when you box one of those, you actually get either a boxed value of type T (Nullable's argument), or a null if the nullable didn't have a value to begin with. And that last case is actually interesting. Turns out, sometimes, I do have a situation when someGuid.HasValue == false. And in those cases, I effectively get a call Html.RenderPartial( "MyView", null ). And what does the HtmlHelper do when the model is null? Believe it or not, it just goes ahead and takes the parent view's model. Regardless of it's type. So, naturally, in those cases, I get an exception saying: "The model item passed into the dictionary is of type 'Parent.View.Model.Type', but this dictionary requires a model item of type 'System.Guid?'" So the question is: how do I make MVC correctly pass new Nullable<Guid> { HasValue = false } instead of trying to grab the parent's model? Note: I did consider wrapping my Guid? in an object of another type, specifically created for this occasion, but this seems completely ridiculous. Don't want to do that as long as there's another way. Note 2: now that I've wrote all this, I've realized that the question may be reduced to how to pass a null for model without ending up with parent's model?

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• How can I export an array from Dynamics AX 2009 via c#?

  - by Steve Homer

  I'm pulling data from Dynamics AX 2009 from c# using the following code snippet. This works fine, except for those cases where the underlying field type is a dimension. I want to be able to "flatten" array types when I return them but can't see any way to do this. Any ideas anyone? axRecord = ax.CreateAxaptaRecord(tableName); axRecord.ExecuteStmt(strQuery); // Loop through the set of retrieved records. using (StreamWriter sw = File.CreateText(path)) { AxaptaObject axDictTable = ax.CreateAxaptaObject("SysDictTable",axRecord.get_Field("tableid")); outputRow = null; List<int> ids = new List<int>(); for (int i = 1; i <= (int)axDictTable.Call("fieldCnt"); i++) { AxaptaObject axDictField = ax.CreateAxaptaObject("DictField", axRecord.get_Field("tableid"), axDictTable.Call("fieldCnt2ID", i)); outputRow += ((string)axDictField.Call("Name")) + ","; ids.Add((int)axDictTable.Call("fieldCnt2ID", i)); } sw.WriteLine(outputRow); while (axRecord.Found) { outputRow = null; foreach(int i in ids) outputRow += axRecord.get_Field(i).ToString().Replace(",", "") + ","; sw.WriteLine(outputRow); axRecord.Next(); } }

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• echo POST array.. or other ideas?

  - by gamerzfuse

  Update: As seen in the Original Questions below, I am looking to echo an array. The problem is that when I send the Moneris gateway to return a POST array to my new file (cart.php) it gets a 500 Internal Server Error. This is the same error I received when it send to the script, which should have worked. Is there any reason that it would always send a 500 Internal Server Error? Cart.php Direct Link Craig ORIGINAL QUESTION: Hello there, I am back for another question. Here is my dilemma: I have a script (ImageFolio Commerce) that hasn't been updated on our server since.. probably 2003. The script had a Payment Gateway (Moneris) manually added to it by the company who offers the script. This costs $1000 to get them to add a gateway. I now have a new client who purchased this business from the previous owner. While switching the account to the new owner's Moneris account, we found out that things have been updated. Long story short.. The Moneris gateway can send 3 types of responses: POST with XML Data POST GET I imagine it is easiest to just use the POST array. I have the file that it sends the response to. As of now the file responds with a Internal Server error, but it does process the order. What I want to do is determine what the POST array is that is being sent, so that I can take it and echo it in a logical manner. Is there a way to capture and echo the entire POST? Or can someone suggest a better method of doing this? Thank you, Craig

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• Modify post data with a custom MVC extension?

  - by Jaxidian

  So I'm looking into writing some custom MVC extensions and the first one I'm attempting to tackle is a FormattedTextBox to handle things such as currency, dates, and times. I have the rendering of it working perfectly, formatting it, working with strong types and everything all golden. However, the problem I'm now running into is cleaning up the formatted stuff when the page posts the data back. Take for example, a currency format. Let's use USD for these examples. When an object has a property as a decimal, the value would be 79.95. Your edit view would be something like: <%= Html.FormattedTextBox(model => Model.Person.HourlyWage, "{0:C}") %> This is all well and good for the GET request, but upon POST, the value is going to be $79.95, which when you assign to that decimal, gets unhappy very quickly and ends up shoving a 0 in there. So my question is, how do I get code working somewhere to work with that value before the MVC Framework goes and starts shoving it back into my ViewModel? I'd much rather this be done server-side than client-side. Thanks!!

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• Passing Object to Service in WCF

  - by hgulyan

  Hi, I have my custom class Customer with its properties. I added DataContract mark above the class and DataMember to properties and it was working fine, but I'm calling a service class's function, passing customer instance as parameter and some of my properties get 0 values. While debugging I can see my properties values and after it gets to the function, some properties' values are 0. Why it can be so? There's no code between this two actions. DataContract mark workes fine, everything's ok. Any suggestions on this issue? I tried to change ByRef to ByVal, but it doesn't change anything. Why it would pass other values right and some of integer types just 0? Maybe the answer is simple, but I can't figure it out. Thank You. <DataContract()> Public Class Customer Private Type_of_clientField As Integer = -1 <DataMember(Order:=1)> Public Property type_of_client() As Integer Get Return Type_of_clientField End Get Set(ByVal value As Integer) Type_of_clientField = value End Set End Property End Class <ServiceContract(SessionMode:=SessionMode.Allowed)> <DataContractFormat()> Public Interface CustomerService <OperationContract()> Function addCustomer(ByRef customer As Customer) As Long End Interface type_of_client properties value is 6 before I call addCustomer function. After it enters that function the value is 0. UPDATE: The issue is in instance creating. When I create an instance of a class on client side, that is stored on service side, some of my properties pass 0 or nothing, but when I call a function of a service class, that returns a new instance of that class, it works fine. What's is the difference? Could that be serialization issue?

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• Demangling typeclass functions in GHC profiler output

  - by Paul Kuliniewicz

  When profiling a Haskell program written in GHC, the names of typeclass functions are mangled in the .prof file to distinguish one instance's implementations of them from another. How can I demangle these names to find out which type's instance it is? For example, suppose I have the following program, where types Fast and Slow both implement Show: import Data.List (foldl') sum' = foldl' (+) 0 data Fast = Fast instance Show Fast where show _ = show $ sum' [1 .. 10] data Slow = Slow instance Show Slow where show _ = show $ sum' [1 .. 100000000] main = putStrLn (show Fast ++ show Slow) I compile with -prof -auto-all -caf-all and run with +RTS -p. In the .prof file that gets generated, I see that the top cost centers are: COST CENTRE MODULE %time %alloc show_an9 Main 71.0 83.3 sum' Main 29.0 16.7 And in the tree, I likewise see (omitting irrelevant lines): individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc main Main 232 1 0.0 0.0 100.0 100.0 show_an9 Main 235 1 71.0 83.3 100.0 100.0 sum' Main 236 0 29.0 16.7 29.0 16.7 show_anx Main 233 1 0.0 0.0 0.0 0.0 How do I figure out that show_an9 is Slow's implementation of show and not Fast's?

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• Creating self-referential tables with polymorphism in SQLALchemy

  - by Jace

  I'm trying to create a db structure in which I have many types of content entities, of which one, a Comment, can be attached to any other. Consider the following: from datetime import datetime from sqlalchemy import create_engine from sqlalchemy import Column, ForeignKey from sqlalchemy import Unicode, Integer, DateTime from sqlalchemy.orm import relation, backref from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() class Entity(Base): __tablename__ = 'entities' id = Column(Integer, primary_key=True) created_at = Column(DateTime, default=datetime.utcnow, nullable=False) edited_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False) type = Column(Unicode(20), nullable=False) __mapper_args__ = {'polymorphic_on': type} # <...insert some models based on Entity...> class Comment(Entity): __tablename__ = 'comments' __mapper_args__ = {'polymorphic_identity': u'comment'} id = Column(None, ForeignKey('entities.id'), primary_key=True) _idref = relation(Entity, foreign_keys=id, primaryjoin=id == Entity.id) attached_to_id = Column(Integer, ForeignKey('entities.id'), nullable=False) #attached_to = relation(Entity, remote_side=[Entity.id]) attached_to = relation(Entity, foreign_keys=attached_to_id, primaryjoin=attached_to_id == Entity.id, backref=backref('comments', cascade="all, delete-orphan")) text = Column(Unicode(255), nullable=False) engine = create_engine('sqlite://', echo=True) Base.metadata.bind = engine Base.metadata.create_all(engine) This seems about right, except SQLAlchemy doesn't like having two foreign keys pointing to the same parent. It says ArgumentError: Can't determine join between 'entities' and 'comments'; tables have more than one foreign key constraint relationship between them. Please specify the 'onclause' of this join explicitly. How do I specify onclause?

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• Creating an API for an ASP.NET MVC site with rate-limiting and caching

  - by Maxim Z.

  Recently, I've been very interested in APIs, specifically in how to create them. For the purpose of this question, let's say that I have created an ASP.NET MVC site that has some data on it; I want to create an API for this site. I have multiple questions about this: What type of API should I create? I know that REST and oData APIs are very popular. What are the pros and cons of each, and how do I implement them? From what I understand so far, REST APIs with ASP.NET MVC would just be actions that return JSON instead of Views, and oData APIs are documented here. How do I handle writing? Reading from both API types is quite simple. However, writing is more complex. With the REST approach, I understand that I can use HTTP POST, but how do I implement authentication? Also, with oData, how does writing work in the first place? How do I implement basic rate-limiting and caching? From my past experience with APIs, these are very important things, so that the API server isn't overloaded. What's the best way to set these two things up? Can I get some sample code? Any code that relates to C# and ASP.NET MVC would be appreciated. Thanks in advance! While this is a broad question, I think it's not too broad... :) There are some similar questions to this one that are about APIs, but I haven't found any that directly address the questions I outlined here.

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• Looking for detailed explanation of Hibernate UserType methods for mutable objects

  - by Tom

  I am creating a custom UserType class in Hibernate. The specific case is for an HL7v3 clinical document (I work in health IT). It is a mutable object and most of the documentation around the Hibernate UserType interface seems to center around immutable types. I want a better understanding of how and when the interface methods are used, specifically: assemble - why two parameters (one Serializable, one Object)? What is the use case for this method? disassemble - should I just implement this method to return a serializable form (e.g. String representation)? When and how is this method invoked? equals - is this for update? read? contention? dirty reads? What are the consequences of simply returning false in most cases? replace - I really don't understand where the three Object parameters come from, when this method is invoked, and what Hibernate expects to return, or how that return value is used. Any pointers would be appreciated. I've searched and read all I can find on the subject, but have not found much documentation at all explaining how these methods are used for mutable objects.

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• Question on boost array initializer

  - by ArunSaha

  I am trying to understand the boost array. The code can be read easily from author's site. In the design rationale, author (Nicolai M. Josuttis) mentioned that the following two types of initialization is possible. boost::array<int,4> a = { { 1, 2, 3 } }; // Line 1 boost::array<int,4> a = { 1, 2, 3 }; // Line 2 In my experiment with g++ (version 4.1.2) Line 1 is working but Line 2 is not. (Line 2 yields the following: warning: missing braces around initializer for 'int [4]' warning: missing initializer for member 'boost::array<int, 4ul>::elems' ) Nevertheless, my main question is, how Line 1 is working? I tried to write a class similar to array.hpp and use statement like Line 1, but that did not work :-(. Can somebody explain me? Is there some boost specific thing happening in Line 1 that I need to be aware of? Thanks in advance. Regards,

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