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  • Creating a [materialised]view from generic data in Oracle/Mysql

    - by Andrew White
    I have a generic datamodel with 3 tables CREATE TABLE Properties ( propertyId int(11) NOT NULL AUTO_INCREMENT, name varchar(80) NOT NULL ) CREATE TABLE Customers ( customerId int(11) NOT NULL AUTO_INCREMENT, customerName varchar(80) NOT NULL ) CREATE TABLE PropertyValues ( propertyId int(11) NOT NULL, customerId int(11) NOT NULL, value varchar(80) NOT NULL ) INSERT INTO Properties VALUES (1, 'Age'); INSERT INTO Properties VALUES (2, 'Weight'); INSERT INTO Customers VALUES (1, 'Bob'); INSERT INTO Customers VALUES (2, 'Tom'); INSERT INTO PropertyValues VALUES (1, 1, '34'); INSERT INTO PropertyValues VALUES (2, 1, '80KG'); INSERT INTO PropertyValues VALUES (1, 2, '24'); INSERT INTO PropertyValues VALUES (2, 2, '53KG'); What I would like to do is create a view that has as columns all the ROWS in Properties and has as rows the entries in Customers. The column values are populated from PropertyValues. e.g. customerId Age Weight 1 34 80KG 2 24 53KG I'm thinking I need a stored procedure to do this and perhaps a materialised view (the entries in the table "Properties" change rarely). Any tips?

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  • what is the best way to analyze user raw query and detect what who want to search

    - by Sadegh
    hi, i am developing a very basic prototype of web search engine and now i want to know what is the best way to analyze user raw query and detect what who want to search. like Google, Bing, Yahoo etc... an example user query is something like this: Google+Maps+"South+Africa"+Brasil+OR+Italy+OR+Spain+-Argentina+Netherland and i want to splite this to a generic list of each term(single) like this: IEnumerable<KeyValuePair<TermType, string>> <TermType.All, "Google"> <TermType.All, "Maps"> <TermType.Exact, "South"> <TermType.Exact, "Africa"> <TermType.Any, "Brazil"> <TermType.Any, "Italy"> <TermType.Any, "Spain"> <TermType.None, "Argentina"> <TermType.None, "Netherland"> i don't want complete code, i want guidance, solution, tips or anything that's help me to write best for anylize user raw query. thanks in advance

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  • A generic error occurred in GDI+, JPEG Image to MemoryStream

    - by madcapnmckay
    Hi, This seems to be a bit of an infamous error all over the web. So much so that I have been unable to find an answer to my problem as my scenario doesn't fit. An exception gets thrown when I save the image to the stream. Weirdly this works perfectly with a png but gives the above error with jpg and gif which is rather confusing. Most similar problem out there relate to saving images to files without permissions. Ironically the solution is to use a memory stream as I am doing.... public static byte[] ConvertImageToByteArray(Image imageToConvert) { using (var ms = new MemoryStream()) { ImageFormat format; switch (imageToConvert.MimeType()) { case "image/png": format = ImageFormat.Png; break; case "image/gif": format = ImageFormat.Gif; break; default: format = ImageFormat.Jpeg; break; } imageToConvert.Save(ms, format); return ms.ToArray(); } } More detail to the exception. The reason this causes so many issues is the lack of explanation :( System.Runtime.InteropServices.ExternalException was unhandled by user code Message="A generic error occurred in GDI+." Source="System.Drawing" ErrorCode=-2147467259 StackTrace: at System.Drawing.Image.Save(Stream stream, ImageCodecInfo encoder, EncoderParameters encoderParams) at System.Drawing.Image.Save(Stream stream, ImageFormat format) at Caldoo.Infrastructure.PhotoEditor.ConvertImageToByteArray(Image imageToConvert) in C:\Users\Ian\SVN\Caldoo\Caldoo.Coordinator\PhotoEditor.cs:line 139 at Caldoo.Web.Controllers.PictureController.Croppable() in C:\Users\Ian\SVN\Caldoo\Caldoo.Web\Controllers\PictureController.cs:line 132 at lambda_method(ExecutionScope , ControllerBase , Object[] ) at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClassa.<InvokeActionMethodWithFilters>b__7() at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation) InnerException: OK things I have tried so far. Cloning the image and working on that. Retrieving the encoder for that MIME passing that with jpeg quality setting. Please can anyone help.

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  • Generic cast type to primitive.

    - by Nix
    Is there a way to do the below? Imagine a generic result wrapper class. Where you have a type and an associated error list. When there is no result to return to the user we will use boolean to indicate success failure. I want to create a constructor that takes in an error list, and if the list is null or count 0, AND the type is a bool/Boolean i want to set it to true.... Seemingly simple, but amazingly not possible. public class Result<T>{ private T valueObject { get;set;} private List<Error> errors{ get;set;} public Result(T valueObj, List<Error> errorList){ this.valueObject = valueObj; this.errors = errorList; } public Result(List<Error> errors) { this.valueObject = default(ReturnType); if (valueObject is Boolean) { //Wont work compile //(valueObject as Boolean) = ((errors == null) || errors.Count == 0); //Compiles but detaches reference //bool temp = ((bool)(valueObject as object)) ; //temp = ((errors == null) || errors.Count == 0); } this.errors = errors; } } } Am I missing something simple? And in general I would prefer to do it without reflection.

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  • Rails: Getting rid of generic "X is invalid" validation errors

    - by DJTripleThreat
    I have a sign-up form that has nested associations/attributes whatever you want to call them. My Hierarchy is this: class User < ActiveRecord::Base acts_as_authentic belongs_to :user_role, :polymorphic => true end class Customer < ActiveRecord::Base has_one :user, :as => :user_role, :dependent => :destroy accepts_nested_attributes_for :user, :allow_destroy => true validates_associated :user end class Employee < ActiveRecord::Base has_one :user, :as => :user_role, :dependent => :destroy accepts_nested_attributes_for :user, :allow_destroy => true validates_associated :user end I have some validation stuff in these classes as well. My problem is that if I try to create and Customer (or Employee etc) with a blank form I get all of the validation errors I should get plus some Generic ones like "User is invalid" and "Customer is invalid" If I iterate through the errors I get something like: user.login can't be blank User is invalid customer.whatever is blah blah blah...etc customer.some_other_error etc etc Since there is at least one invalid field in the nested User model, an extra "X is invalid" message is added to the list of errors. This gets confusing to my client and so I'm wondering if there is a quick way to do this instead of having to filer through the errors myself.

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  • Understanding the workflow of the messages in a generic server implementation in Erlang

    - by Chiron
    The following code is from "Programming Erlang, 2nd Edition". It is an example of how to implement a generic server in Erlang. -module(server1). -export([start/2, rpc/2]). start(Name, Mod) -> register(Name, spawn(fun() -> loop(Name, Mod, Mod:init()) end)). rpc(Name, Request) -> Name ! {self(), Request}, receive {Name, Response} -> Response end. loop(Name, Mod, State) -> receive {From, Request} -> {Response, State1} = Mod:handle(Request, State), From ! {Name, Response}, loop(Name, Mod, State1) end. -module(name_server). -export([init/0, add/2, find/1, handle/2]). -import(server1, [rpc/2]). %% client routines add(Name, Place) -> rpc(name_server, {add, Name, Place}). find(Name) -> rpc(name_server, {find, Name}). %% callback routines init() -> dict:new(). handle({add, Name, Place}, Dict) -> {ok, dict:store(Name, Place, Dict)}; handle({find, Name}, Dict) -> {dict:find(Name, Dict), Dict}. server1:start(name_server, name_server). name_server:add(joe, "at home"). name_server:find(joe). I tried so hard to understand the workflow of the messages. Would you please help me to understand the workflow of this server implementation during the executing of the functions: server1:start, name_server:add and name_server:find?

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  • JVM GC demote object to eden space?

    - by Kevin
    I'm guessing this isn't possible...but here goes. My understanding is that eden space is cheaper to collect than old gen space, especially when you start getting into very large heaps. Large heaps tend to come up with long running applications (server apps) and server apps a lot of the time want to use some kind of caches. Caches with some kind of eviction (LRU) tend to defeat some assumptions that GC makes (temporary objects die quickly). So cache evictions end up filling up old gen faster than you'd like and you end up with a more costly old gen collection. Now, it seems like this sort of thing could be avoided if java provided a way to mark a reference as about to die (delete keyword)? The difference between this and c++ is that the use is optional. And calling delete does not actually delete the object, but rather is a hint to the GC that it should demote the object back to Eden space (where it will be more easily collected). I'm guessing this feature doesn't exist, but, why not (is there a reason it's a bad idea)?

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  • How to create a generic list in this wierd case in c#

    - by Marc Bettex
    Hello, In my program, I have a class A which is extended by B, C and many more classes. I have a method GetInstance() which returns a instance of B or C (or of one of the other child), but I don't know which one, so the return type of the method is A. In the method CreateGenericList(), I have a variable v of type A, which is in fact either a B, a C or another child type and I want to create a generic list of the proper type, i.e. List<B> if v is a B or List<C> if v is a C, ... Currently I do it by using reflection, which works, but this is extremely slow. I wanted to know if there is another way to to it, which doesn't use reflection. Here is an example of the code of my problem: class A { } class B : A { } class C : A { } // More childs of A. class Program { static A GetInstance() { // returns an instance of B or C } static void CreateGenericList() { A v = Program.GetInstance(); IList genericList = // Here I want an instance of List<B> or List<C> or ... depending of the real type of v, not a List<A>. } } I tried the following hack. I call the following method, hoping the type inferencer will guess the type of model, but it doesn't work and return a List<A>. I believe that because c# is statically typed, T is resolved as A and not as the real type of model at runtime. static List<T> CreateGenericListFromModel<T>(T model) where T : A { return new List<T> (); } Does anybody have a solution to that problem that doesn't use reflection or that it is impossible to solve that problem without reflection? Thank you very much, Marc

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  • Generic version control strategy for select table data within a heavily normalized database

    - by leppie
    Hi Sorry for the long winded title, but the requirement/problem is rather specific. With reference to the following sample (but very simplified) structure (in psuedo SQL), I hope to explain it a bit better. TABLE StructureName { Id GUID PK, Name varchar(50) NOT NULL } TABLE Structure { Id GUID PK, ParentId GUID (FK to Structure), NameId GUID (FK to StructureName) NOT NULL } TABLE Something { Id GUID PK, RootStructureId GUID (FK to Structure) NOT NULL } As one can see, Structure is a simple tree structure (not worried about ordering of children for the problem). StructureName is a simplification of a translation system. Finally 'Something' is simply something referencing the tree's root structure. This is just one of many tables that need to be versioned, but this one serves as a good example for most cases. There is a requirement to version to any changes to the name and/or the tree 'layout' of the Structure table. Previous versions should always be available. There seems to be a few possibilities to tackle this issue, like copying the entire structure, but most approaches causes one to 'loose' referential integrity. Example if one followed this approach, one would have to make a duplicate of the 'Something' record, given that the root structure will be a new record, and have a new ID. Other avenues of possible solutions are looking into how Wiki's handle this or go a lot further and look how proper version control systems work. Currently, I feel a bit clueless how to proceed on this in a generic way. Any ideas will be greatly appreciated. Thanks leppie

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  • how can modify or add new item into generic list of string's

    - by Sadegh
    hi, i want to remove some pretty words in list of words. public System.String CleanNoiseWord(System.String word) { string key = word; if (word.Length <= 2) key = System.String.Empty; else key = word; //other validation here return key; } public IList<System.String> Clean(IList<System.String> words) { var oldWords = words; IList<System.String> newWords = new string[oldWords.Count()]; string key; var i = 0; foreach (System.String word in oldWords) { key = this.CleanNoiseWord(word); if (!string.IsNullOrEmpty(key)) { newWords.RemoveAt(i); newWords.Insert(i++, key); } } return newWords.Distinct().ToList(); } but i can't add, remove or insert any thing in list! and exception NotSupportedException occured Collection was of a fixed size. how i can modify or add new item into generic list of string's?

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  • Generic Class Vb.net

    - by KoolKabin
    hi guys, I am stuck with a problem about generic classes. I am confused how I call the constructor with parameters. My interface: Public Interface IDBObject Sub [Get](ByRef DataRow As DataRow) Property UIN() As Integer End Interface My Child Class: Public Class User Implements IDBObject Public Sub [Get](ByRef DataRow As System.Data.DataRow) Implements IDBObject.Get End Sub Public Property UIN() As Integer Implements IDBObject.UIN Get End Get Set(ByVal value As Integer) End Set End Property End Class My Next Class: Public Class Users Inherits DBLayer(Of User) #Region " Standard Methods " #End Region End Class My DBObject Class: Public Class DBLayer(Of DBObject As {New, IDBObject}) Public Shared Function GetData() As List(Of DBObject) Dim QueryString As String = "SELECT * ***;" Dim Dataset As DataSet = New DataSet() Dim DataList As List(Of DBObject) = New List(Of DBObject) Try Dataset = Query(QueryString) For Each DataRow As DataRow In Dataset.Tables(0).Rows **DataList.Add(New DBObject(DataRow))** Next Catch ex As Exception DataList = Nothing End Try Return DataList End Function End Class I get error in the starred area of the DBLayer Object. What might be the possible reason? what can I do to fix it? I even want to add New(byval someval as datatype) in IDBObject interface for overloading construction. but it also gives an error? how can i do it? Adding Sub New(ByVal DataRow As DataRow) in IDBObject producess following error 'Sub New' cannot be declared in an interface. Error Produced in DBLayer Object line: DataList.Add(New DBObject(DataRow)) Msg: Arguments cannot be passed to a 'New' used on a type parameter.

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  • Linq to xml, retreaving generic interface-based list

    - by Rita
    I have an xml document that looks like this <Elements> <Element> <DisplayName /> <Type /> </Element> </Elements> I have an interface, interface IElement { string DisplayName {get;} } and a couple of derived classes: public class AElement: IElement public class BElement: IElement What I want to do, is to write the most efficient query to iterate through the xml and create a list of IElement, containing AElement or BElement, based on the 'Type' property in the xml. So far I have this: IEnumerable<AElement> elements = from xmlElement in XElement.Load(path).Elements("Element") where xmlElement.Element("type").Value == "AElement" select new AElement(xmlElement.Element("DisplayName").Value); return elements.Cast<IElement>().ToList(); But this is only for AElement, is there a way to add BElement in the same query, and also make it generic IEnumerable? Or would I have to run this query once for each derived type?

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  • What is the best way to find a processed memory allocations in terms of C# objects

    - by Shantaram
    I have written various C# console based applications, some of them long running some not, which can over time have a large memory foot print. When looking at the windows perofrmance monitor via the task manager, the same question keeps cropping up in my mind; how do I get a break down of the number objects by type that are contributing to this footprint; and which of those are f-reachable and those which aren't and hence can be collected. On numerous occasions I've performed a code inspection to ensure that I am not unnecessarily holding on objects longer than required and disposing of objects with the using construct. I have also recently looked at employing the CG.Collect method when I have released a large number of objects (for example held in a collection which has just been cleared). However, I am not so sure that this made that much difference, so I threw that code away. I am guessing that there are tools in sysinternals suite than can help to resolve these memory type quiestions but I am not sure which and how to use them. The alternative would be to pay for a third party profiling tool such as JetBrains dotTrace; but I need to make sure that I've explored the free options first before going cap in hand to my manager.

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  • NHibernate. Initiate save collection at saving parent

    - by Andrew Kalashnikov
    Hello, colleagues. I've got a problem at saving my entity. MApping: ?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Clients.Core" namespace="Clients.Core.Domains"> <class name="Sales, Clients.Core" table='sales'> <id name="Id" unsaved-value="0"> <column name="id" not-null="true"/> <generator class="native"/> </id> <property name="Guid"> <column name="guid"/> </property> <set name="Accounts" table="sales_users" lazy="false"> <key column="sales_id" /> <element column="user_id" type="Int32" /> </set> Domain: public class Sales : BaseDomain { ICollection<int> accounts = new List<int>(); public virtual ICollection<int> Accounts { get { return accounts; } set { accounts = value; } } public Sales() { } } When I save Sales object Account collection don't save at sales_users table. What should I do for saving it? Please don't advice me use classes inside List Thanks a lot.

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  • generic binary Search in c#

    - by Pro_Zeck
    Below is my Generic Binary Search it works ok with the intgers type array it finds all the elements in it . But the Problem Arises when i use a string array to find any string data. It runs ok for the first index and last index elements but i cant find the middle elements. Stringarray = new string[] { "b", "a", "ab", "abc", "c" }; public static void BinarySearch<T>(T[] array, T searchFor, Comparer<T> comparer) { int high, low, mid; high = array.Length - 1; low = 0; if (array[0].Equals(searchFor)) Console.WriteLine("Value {0} Found At Index {1}",array[0],0); else if (array[high].Equals(searchFor)) Console.WriteLine("Value {0} Found At Index {1}", array[high], high); else { while (low <= high) { mid = (high + low) / 2; if (comparer.Compare(array[mid], searchFor) == 0) { Console.WriteLine("Value {0} Found At Index {1}", array[mid], mid); break; } else { if (comparer.Compare(searchFor, array[mid]) > 0) high = mid + 1; else low = mid + 1; } } if (low > high) { Console.WriteLine("Value Not Found In the Collection"); } } }

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  • N Tiers with SubSonic 3, Dirty Columns collection is alwayes empty on update

    - by Adel
    Hello guys here is what i am doing, and not working for me. I have a DAL generated with SubSonic 3 ActiveRecord template, i have a service layer (business layer if you well) that have mixture of facade and some validation. say i have a method on the Service layer like public void UpdateClient(Client client); in my GUI i create a Client object fill it with some data with ID and pass it to the service method and this never worked, the dirty columns collection (that track which columns are altered in order to use more efficant update statment) is alwayes empty. if i tried to get the object from database inside my GUI then pass it to the service method it's not working either. the only scenario i find working is if i query the object from the database and call Update() on the same context all inside my GUI and this defeats the whole service layer i've created. however for insert and delete everything working fine, i wonder if this have to do something with object tracking but what i know is SubSonic don't do that. please advice. thanks. Adel.

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  • Self referencing userdata and garbage collection

    - by drtwox
    Because my userdata objects reference themselves, I need to delete and nil a variable for the garbage collector to work. Lua code: obj = object:new() -- -- Some time later obj:delete() -- Removes the self reference obj = nil -- Ready for collection C Code: typedef struct { int self; // Reference to the object // Other members and function references removed } Object; // Called from Lua to create a new object static int object_new( lua_State *L ) { Object *obj = lua_newuserdata( L, sizeof( Object ) ); // Create the 'self' reference, userdata is on the stack top obj->self = luaL_ref( L, LUA_REGISTRYINDEX ); // Put the userdata back on the stack before returning lua_rawgeti( L, LUA_REGISTRYINDEX, obj->self ); // The object pointer is also stored outside of Lua for processing in C return 1; } // Called by Lua to delete an object static int object_delete( lua_State *L ) { Object *obj = lua_touserdata( L, 1 ); // Remove the objects self reference luaL_unref( L, LUA_REGISTRYINDEX, obj->self ); return 0; } Is there some way I can set the object to nil in Lua, and have the delete() method called automatically? Alternatively, can the delete method nil all variables that reference the object? Can the self reference be made 'weak'?

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  • Question About Fk refrence in The Collection

    - by Ahmed
    Hi , i have 2 entities : ( person ) & (Address) with follwing mapping : <class name="Adress" table="Adress" lazy="false"> <id name="Id" column="Id"> <generator class="native" /> </id> <many-to-one name="Person" class="Person"> <column name="PersonId" /> </many-to-one> </class> <class name="Person" table="Person" lazy="false"> <id name="PersonId" column="PersonId"> <generator class="native" /> </id> <property name="Name" column="Name" type="String" not-null="true" /> <set name="Adresses" lazy="true" inverse="true" cascade="save-update"> <key> <column name="PersonId" /> </key> <one-to-many class="Adress" /> </set> </class> my propblem is that when i set Adrees.Person with new object of person ,The collection person.Adresses doesn't update itself . should i update every end role of the association to be updated in the two both? another thing : if i updated the Fk manually like this : Adress.PersonId it doesn't break or change association. does this is Nhibernte behavior ? thanks in advance , i am waiting for your experiencies

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  • Databinding expression for retrieving value of related collection using LINQ

    - by joshb
    I have a GridView that is bound to a LINQDataSource control that is returning a collection of customers. Within my DataGrid I need to display the home phone number of a customer, if they have one. The phone numbers of a customer are stored in a separate table with a foreign key pointing to the customer table. The following binding expression gets me the first phone number for a customer: <asp:TemplateField HeaderText="LastName" SortExpression="LastName"> <ItemTemplate> <asp:Label ID="PhoneLabel" runat="server" Text='<%# Eval("Phones[0].PhoneNumber") %>'></asp:Label> </ItemTemplate> </asp:TemplateField> I need to figure out how to get the home phone number specifically (filter based on phone type) and handle the scenario where the customer does not have a home phone in the database. Right now it's throwing an out of range exception if the customer does not have any phone numbers. I've tried using the Where operator with a lambda expression to filter the phone type but it doesn't work: <%# Eval("Phones.Where(p => p.PhoneTypeId == 2).PhoneNumber") %> Solutions or links to any good articles on the subject would be much appreciated.

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  • Nested model form with collection in Rails 2.3

    - by kristian nissen
    How can I make this work in Rails 2.3? class Magazine < ActiveRecord::Base has_many :magazinepages end class Magazinepage < ActiveRecord::Base belongs_to :magazine end and then in the controller: def new @magazine = Magazine.new @magazinepages = @magazine.magazinepages.build end and then the form: <% form_for(@magazine) do |f| %> <%= error_messages_for :magazine %> <%= error_messages_for :magazinepages %> <fieldset> <legend><%= t('new_magazine') %></legend> <p> <%= f.label :title %> <%= f.text_field :title %> </p> <fieldset> <legend><%= t('new_magazine_pages') %> <% f.fields_for :magazinepages do |p| %> <p> <%= p.label :name %> <%= p.text_field :name %> </p> <p> <%= p.file_field :filepath %> </p> <% end %> </fieldset> <p> <%= f.submit :save %> </p> </fieldset> <% end %> problem is, if I want to submit a collection of magazinepages, activerecord complaints because it's expected a model and not an array. create action: def create @magazine = Magazine.new params[:magazine] @magazine.save ? redirect_to(@magazine) : render(:action => 'new') end

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  • Code Analysis Warning CA1004 with generic method

    - by Vaccano
    I have the following generic method: // Load an object from the disk public static T DeserializeObject<T>(String filename) where T : class { XmlSerializer xmlSerializer = new XmlSerializer(typeof(T)); try { TextReader textReader = new StreamReader(filename); var result = (T)xmlSerializer.Deserialize(textReader); textReader.Close(); return result; } catch (FileNotFoundException) { } return null; } When I compile I get the following warning: CA1004 : Microsoft.Design : Consider a design where 'MiscHelpers.DeserializeObject(string)' doesn't require explicit type parameter 'T' in any call to it. I have considered this and I don't know a way to do what it requests with out limiting the types that can be deserialized. I freely admit that I might be missing an easy way to fix this. But if I am not, then is my only recourse to suppress this warning? I have a clean project with no warnings or messages. I would like to keep it that way. I guess I am asking "why this is a warning?" At best this seems like it should be a message. And even that seems a bit much. Either it can or it can't be fixed. If it can't then you are just stuck with the warning with no recourse but suppressing it. Am I wrong?

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  • Can't add/remove items from a collection while foreach is iterating over it

    - by flockofcode
    If I make my own implementation of IEnumerator interface, then I am able ( inside foreach statement )to add or remove items from a albumsList without generating an exception.But if foreach statement uses IEnumerator supplied by albumsList, then trying to add/delete ( inside the foreach )items from albumsList will result in exception: class Program { static void Main(string[] args) { string[] rockAlbums = { "rock", "roll", "rain dogs" }; ArrayList albumsList = new ArrayList(rockAlbums); AlbumsCollection ac = new AlbumsCollection(albumsList); foreach (string item in ac) { Console.WriteLine(item); albumsList.Remove(item); //works } foreach (string item in albumsList) { albumsList.Remove(item); //exception } } class MyEnumerator : IEnumerator { ArrayList table; int _current = -1; public Object Current { get { return table[_current]; } } public bool MoveNext() { if (_current + 1 < table.Count) { _current++; return true; } else return false; } public void Reset() { _current = -1; } public MyEnumerator(ArrayList albums) { this.table = albums; } } class AlbumsCollection : IEnumerable { public ArrayList albums; public IEnumerator GetEnumerator() { return new MyEnumerator(this.albums); } public AlbumsCollection(ArrayList albums) { this.albums = albums; } } } a) I assume code that throws exception ( when using IEnumerator implementation A supplied by albumsList ) is located inside A? b) If I want to be able to add/remove items from a collection ( while foreach is iterating over it), will I always need to provide my own implementation of IEnumerator interface, or can albumsList be set to allow adding/removing items? thank you

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  • Multiple generic types in one container

    - by Lirik
    I was looking at the answer of this question regarding multiple generic types in one container and I can't really get it to work: the properties of the Metadata class are not visible, since the abstract class doesn't have them. Here is a slightly modified version of the code in the original question: public abstract class Metadata { } public class Metadata<T> : Metadata { // ... some other meta data public T Function{ get; set; } } List<Metadata> metadataObjects; metadataObjects.Add(new Metadata<Func<double,double>>()); metadataObjects.Add(new Metadata<Func<int,double>>()); metadataObjects.Add(new Metadata<Func<double,int>>()); foreach( Metadata md in metadataObjects) { var tmp = md.Function; // <-- Error: does not contain a definition for Function } The exact error is: error CS1061: 'Metadata' does not contain a definition for 'Function' and no extension method 'Function' accepting a first argument of type 'Metadata' could be found (are you missing a using directive or an assembly reference?) I believe it's because the abstract class does not define the property Function, thus the whole effort is completely useless. Is there a way that we can get the properties?

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  • A generic C++ library that provides QtConcurrent functionality?

    - by Lucas
    QtConcurrent is awesome. I'll let the Qt docs speak for themselves: QtConcurrent includes functional programming style APIs for parallel list processing, including a MapReduce and FilterReduce implementation for shared-memory (non-distributed) systems, and classes for managing asynchronous computations in GUI applications. For instance, you give QtConcurrent::map() an iterable sequence and a function that accepts items of the type stored in the sequence, and that function is applied to all the items in the collection. This is done in a multi-threaded manner, with a thread pool equal to the number of logical CPU's on the system. There are plenty of other function in QtConcurrent, like filter(), filteredReduced() etc. The standard CompSci map/reduce functions and the like. I'm totally in love with this, but I'm starting work on an OSS project that will not be using the Qt framework. It's a library, and I don't want to force others to depend on such a large framework like Qt. I'm trying to keep external dependencies to a minimum (it's the decent thing to do). I'm looking for a generic C++ framework that provides me with the same/similar high-level primitives that QtConcurrent does. AFAIK boost has nothing like this (I may be wrong though). boost::thread is very low-level compared to what I'm looking for. I know C# has something very similar with their Parallel Extensions so I know this isn't a Qt-only idea. What do you suggest I use?

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  • Java constructor using generic types

    - by Beer Me
    I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method breweryMethod() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // breweryMethod() is an instance method // of Brewery, of which <T> is a subclass (right?) c.breweryMethod(); // "The method breweryMethod() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void brewerySubClassMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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