say - Page 623 - Developer IT

Transitive SQL query on same table

- by MiKu

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.net Class "is not a member of" Class .. even though it is?

- by Matt Thrower

Hi, Looking over some older code, I've run into a strange namespace error. Let's say I have two projects, HelperProject and WebProject. The full namespace of each - as given in application properties - is myEmployer.HelperProject and myEmployer.Web.WebProject. The pages in the web project are full of statements that use classes from the helper project. There are no imports/using statements but there is a reference to the helper project added in the bin. A few example lines might be: myEmployer.HelperProject.StringHelper.GetFixedLengthText(Text, "", Me.Width, 11) myEmploter.HelperProject.Utils.StringHelper.EstimatePixelLength(Text, 11) However every line that is written in this manner is throwing the error 'HelperProject' is not a member of 'myEmployer'. If you declare the statements like this: HelperProject.StringHelper.GetFixedLengthText(Text, "", Me.Width, 11) HelperProject.Utils.StringHelper.EstimatePixelLength(Text, 11) Everything seems fine. In the solution object browser and the bin folder, HelperProject appears with its full namespace, myEmployer.HelperProject. I don't want to have to change all the statements, and besides I suspect this is masking a more fundamental problem here. But I have no idea what's going on. Can anyone offer any pointers please? Cheers, Matt

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Using multiple sockets, is non-blocking or blocking with select better?

- by JPhi1618

Lets say I have a server program that can accept connections from 10 (or more) different clients. The clients send data at random which is received by the server, but it is certain that at least one client will be sending data every update. The server cannot wait for information to arrive because it has other processing to do. Aside from using asynchronous sockets, I see two options: Make all sockets non-blocking. In a loop, call recv on each socket and allow it to fail with WSAEWOULDBLOCK if there is no data available and if I happen to get some data, then keep it. Leave the sockets as blocking. Add all sockets to a fd_set and call select(). If the return value is non-zero (which it will be most of the time), loop through all the sockets to find the appropriate number of readable sockets with FD_ISSET() and only call recv on the readable sockets. The first option will create a lot more calls to the recv function. The second method is a bigger pain from a programming perspective because of all the FD_SET and FD_ISSET looping. Which method (or another method) is preferred? Is avoiding the overhead on letting recv fail on a non-blocking socket worth the hassle of calling select()? I think I understand both methods and I have tried both with success, but I don't know if one way is considered better or optimal. Only knowledgeable replies please!

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C# reflexion, cloning

- by Enriquev

Say I have this class Myclass that contains this method: public class MyClass { public int MyProperty { get; set; } public int MySecondProperty { get; set; } public MyOtherClass subClass { get; set; } public object clone<T>(object original, T emptyObj) { FieldInfo[] fis = this.GetType().GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic); object tempMyClass = Activator.CreateInstance(typeof(T)); foreach (FieldInfo fi in fis) { if (fi.FieldType.Namespace != original.GetType().Namespace) fi.SetValue(tempMyClass, fi.GetValue(original)); else fi.SetValue(tempMyClass, this.clone(fi.GetValue(original), fi.GetValue(original))); } return tempMyClass; } } Then this class: public class MyOtherClass { public int MyProperty777 { get; set; } } when I do this: MyClass a = new MyClass { MyProperty = 1, MySecondProperty = 2, subClass = new MyOtherClass() { MyProperty777 = -1 } }; MyClass b = a.clone(a, a) as MyClass; how come on the second call to clone, T is of type object and not of type MyOtherClass

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MS SQL datetime precision problem

- by Nailuj

I have a situation where two persons might work on the same order (stored in an MS SQL database) from two different computers. To prevent data loss in the case where one would save his copy of the order first, and then a little later the second would save his copy and overwrite the first, I've added a check against the lastSaved field (datetime) before saving. The code looks roughly like this: private bool orderIsChangedByOtherUser(Order localOrderCopy) { // Look up fresh version of the order from the DB Order databaseOrder = orderService.GetByOrderId(localOrderCopy.Id); if (databaseOrder != null && databaseOrder.LastSaved > localOrderCopy.LastSaved) { return true; } else { return false; } } This works for most of the time, but I have found one small bug. If orderIsChangedByOtherUser returns false, the local copy will have its lastSaved updated to the current time and then be persisted to the database. The value of lastSaved in the local copy and the DB should now be the same. However, if orderIsChangedByOtherUser is run again, it sometimes returns true even though no other user has made changes to the DB. When debugging in Visual Studio, databaseOrder.LastSaved and localOrderCopy.LastSaved appear to have the same value, but when looking closer they some times differ by a few milliseconds. I found this article with a short notice on the millisecond precision for datetime in SQL: Another problem is that SQL Server stores DATETIME with a precision of 3.33 milliseconds (0. 00333 seconds). The solution I could think of for this problem, is to compare the two datetimes and consider them equal if they differ by less than say 10 milliseconds. My question to you is then: are there any better/safer ways to compare two datetime values in MS SQL to see if they are exactly the same?

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SmartGwt DateItem useTextField=true - how to make text entry field UNeditable

- by Paul

Since I can't figure out how to solve my problem presented here I'm thinking for the moment at a temporary solution. I have a smartgwt DateItem widget: DateItem date = new DateItem("Adate"); date.setWidth(120); date.setWrapTitle(false); date.setAttribute("useTextField", true); date.setAttribute("inputFormat", "yyyy/MM/dd"); date.setAttribute("displayFormat", "toJapanShortDate"); Because the attribute useTextField is set to true we can see the text entry field. How can I make this text entry field to be uneditable. Actually I want to have only the possibility to choose the date from calendar and not to change it manually. Resolved - the issue exposed above - thanks to @RAS user. TextItem textItem = new TextItem(); textItem.setAttribute("readOnly", true); date.setAttribute("textFieldProperties", textItem); Related link But I have now another issue: The date chooser won't show the date on the text field but Today's date. For example, enter 30/05/2009 on the text field, go to another field, then come back on click on the date chooser and the selected day will be Today's date instead on June 30th, 2009. Which is the reason for this? Can this be solved? Also let's say I let to the user to opportunity to manually modify the date - can I put some validators on it? Thank you.

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I am using relational division with EAV, but I need to find results in EAV that have some of the cat

- by NewToDB

I have two tables: CREATE TABLE EAV ( subscriber_id INT(1) NOT NULL DEFAULT '0', attribute_id CHAR(62) NOT NULL DEFAULT '', attribute_value CHAR(62) NOT NULL DEFAULT '', PRIMARY KEY (subscriber_id,attribute_id) ) INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (1,'color','red') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (1,'size','xl') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (1,'garment','shirt') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (2,'color','red') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (2,'size','xl') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (2,'garment','pants') INSERT INTO EAV (subscriber_id, attribute_id, attribute_value) VALUES (3,'garment','pants') CREATE TABLE CRITERIA ( attribute_id CHAR(62) NOT NULL DEFAULT '', attribute_value CHAR(62) NOT NULL DEFAULT '' ) INSERT INTO CRITERIA (attribute_id, attribute_value) VALUES ('color', 'red') INSERT INTO CRITERIA (attribute_id, attribute_value) VALUES ('size', 'xl') To find all subscribers in the EAV that match my criteria, I use relational division: SELECT DISTINCT(subscriber_id) FROM EAV WHERE subscriber_id IN (SELECT E.subscriber_id FROM EAV AS E JOIN CRITERIA AS CR ON E.attribute_id = CR.attribute_id AND E.attribute_value = CR.attribute_value GROUP BY E.subscriber_id HAVING COUNT() = (SELECT COUNT() FROM CRITERIA)) This gives me an unique list of subscribers who have all the criteria. So that means I get back subscriber 1 and 2 since they are looking for the color red and size xl, and that's exactly my criteria. But what if I want to extend this so that I also get subscriber 3 since this subscriber didn't specifically say what color or size they want (ie. there is no entry for attribute 'color' or 'size' in the EAV table for subscriber 3). Given my current design, is there a way I can extend my query to include subscribers that have zero or more of the attributes defined, and if they do have the attribute defined, then it must match the criteria? Or is there a better way to design the table to aid in querying?

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SHLoadImageFile(L"\\Program Files\\TrainingApp\\background.png"); whats that L in the argument for?

- by ashishsony

Hi, ive been working on c++ on linux for the past 2 years,and switched to windows c++ programming recently. can anyone tell me what that L is there in the argument of the function: SHLoadImageFile(L"\\Program Files\\TrainingApp\\background.png"); and on viewing certain sample code in MSVS C++ i came across hundereds of typedefs like.. LPARAM// typedef LONG_PTR LPARAM... here LONG_PTR is again typedef as __w64 long WPARAM// typedef UINT_PTR WPARAM... so there is a lot of chained typedefs.. I never saw this much of typedef chaining on c++ programming on linux using gcc.. what i want to say is that it just creates more confusion in this way for windows application programming.. while ive seen application programming on linux using frameworks like Qt.. there such things are rarely used.. so is there specific purpose in typedefining again and again on MSVSC++?? for eg.. there are typdefs like typedef int BOOL; whats the use of this when normal bool is available already..?? there are hundred other cases ive come across where just to decide what data type to use becomes so difficult.. it becomes difficult to understand a pre written code in this fashion too.. Thanks.

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Finding values from a table that are not in a grouping of another table and what group that value

- by Bkins

I hope I am not missing something very simple here. I have done a Google search(es) and searched through stackoverflow. Here is the situation: For simplicity's sake let's say I have a table called "PeoplesDocs", in a SQL Server 2008 DB, that holds a bunch of people and all the documents that they own. So one person can have several documents. I also have a table called "RequiredDocs" that simply holds all the documents that a person should have. Here is sort of what it looks like: PeoplesDocs: PersonID DocID -------- ----- 1 A 1 B 1 C 1 D 2 C 2 D 3 A 3 B 3 C RequiredDocs: DocID DocName ----- --------- A DocumentA B DocumentB C DocumentC D DocumentD How do I write a SQL query that returns some variation of: PersonID MissingDocs -------- ----------- 2 DocumentA 2 DocumentB 3 DocumentD I have tried, and most of my searching has pointed to, something like: SELECT DocID FROM DocsRequired WHERE NOT EXIST IN ( SELECT DocID FROM PeoplesDocs) but obviously this will not return anything in this example because everyone has at least one of the documents. Also, if a person does not have any documents then there will be one record in the PeoplesDocs table with the DocID set to NULL. Thank you in advance for any help you can provide, Ben

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List of objects or parallel arrays of properties?

- by Headcrab

The question is, basically: what would be more preferable, both performance-wise and design-wise - to have a list of objects of a Python class or to have several lists of numerical properties? I am writing some sort of a scientific simulation which involves a rather large system of interacting particles. For simplicity, let's say we have a set of balls bouncing inside a box so each ball has a number of numerical properties, like x-y-z-coordinates, diameter, mass, velocity vector and so on. How to store the system better? Two major options I can think of are: to make a class "Ball" with those properties and some methods, then store a list of objects of the class, e. g. [b1, b2, b3, ...bn, ...], where for each bn we can access bn.x, bn.y, bn.mass and so on; to make an array of numbers for each property, then for each i-th "ball" we can access it's 'x' coordinate as xs[i], 'y' coordinate as ys[i], 'mass' as masses[i] and so on; To me it seems that the first option represents a better design. The second option looks somewhat uglier, but might be better in terms of performance, and it could be easier to use it with numpy and scipy, which I try to use as much as I can. I am still not sure if Python will be fast enough, so it may be necessary to rewrite it in C++ or something, after initial prototyping in Python. Would the choice of data representation be different for C/C++? What about a hybrid approach, e.g. Python with C++ extension?

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Linux RFID reader HID Device not matching driver

- by blietaer

Hello, I got a RFID reader (GigaTek PCR330A-00) that is meant to be recognized under linux/windows as a (Human Interface Device) keyboard/USB. I hate to say this but it is working as a charm under Win7 but not "really" under Linux. Under Debian-like distros (x/k/Ubuntu, Debian,..), or Gentoo, or... I just can't have the device working at all: the device scan well (it has its USB 5V, so it is happy/beeping/blinking) something happened in the dmesg, but no immediate screen display of the RFID Tag code as expected (and seen under win7) Support is claiming it is ok under RHEL or SLED "enterprises" distros... and I must admit I saw it working under a RHEL4... I tried stealing the driver but did not succeed having my reader working... My question is thus double: 1./ How can I hack the kernel to add support to my device (simply register PID/VID?) ? 2./ What is different at all in a "enterprise" proprietary distro? how can I re-use it? Thank you for any hint/help. Cheers,

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C# - parse content away from structure in a binary file

- by Jeff Godfrey

Using C#, I need to read a packed binary file created using FORTRAN. The file is stored in an "Unformatted Sequential" format as described here (about half-way down the page in the "Unformatted Sequential Files" section): http://www.tacc.utexas.edu/services/userguides/intel8/fc/f_ug1/pggfmsp.htm As you can see from the URL, the file is organized into "chunks" of 130 bytes or less and includes 2 length bytes (inserted by the FORTRAN compiler) surrounding each chunk. So, I need to find an efficient way to parse the actual file payload away from the compiler-inserted formatting. Once I've extracted the actual payload from the file, I'll then need to parse it up into its varying data types. That'll be the next exercise. My first thoughts are to slurp up the entire file into a byte array using File.ReadAllBytes. Then, just iterate through the bytes, skipping the formatting and transferring the actual data to a second byte array. In the end, that second byte array should contain the actual file contents minus all the formatting, which I'd then need to go back through to get what I need. As I'm fairly new to C#, I thought there might be a better, more accepted way of tackling this. Also, in case it's helpful, these files could be fairly large (say 30MB), though most will be much smaller...

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How reliable is DateTime.UtcNow in Silverlight applications?

- by Edward Tanguay

I have a silverlight application which users will be running in various time zones. These applications load their data from the server upon start up, then cache it in IsolatedStorage. When I make changes to the data on the server, I want to be able to change the "last updated time" so that all silverlight clients download the newest data the next time they check this date. However, I'm a bit confused as to how to handle the time zone issue since a if the server is in New York and the update time is set to 2010-01-01 17:00:00 and a client in Seattle checks compares it to its local time of 2010-01-01 14:00:00 it won't update and will continue to provide old data for three more hours. My solution is to always post the update time in UTC time, not with the time on the server, then make the Silverlight app check with DateTime.UtcNow. Is this as easy as it sounds or are their issues with this, e.g. that timezones are not set correctly on computers and hence the SilverlightApp does not report the correct UTC time. Can anyone say from experience how likely it is that using DateTime.UtcNow like this for cache refreshing will work in all cases? If DateTime.UtcNow is not reliable, I will just use an incremented "DataVersion" integer but there are other scenarios in which getting time zone sychronization down would make it useful to thoroughly understand how to solve this in silverlight apps.

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Send parameters to a web service.

- by Alejandra Meraz

Before I start: I'm programming for Iphone, using objective C. I have already implemented a call to a web service function using NSURLRequest and NSURLConnection. The function then returns a XML with the info I need. The code is as follows: NSURL *url = [NSURL URLWithString:@"http://myWebService/function"]; NSMutableURLRequest theRequest = [[NSMutableURLRequest alloc] initWithURL:url]; NSURLConnection theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self]; i also implemented the methods didRecieveResponse didRecieveAuthenticationChallenge didRecievedData didFailWithError connectionDidFinishLoading. And it works perfectly. Now I need to send 2 parameters to the function: "location" and "module". I tried using the following modification: NSMutableURLRequest theRequest = [[NSMutableURLRequest alloc] initWithURL:url]; [theRequest setValue:@"USA" forHTTPHeaderField:@"location"]; [theRequest setValue:@"DEVELOPMENT" forHTTPHeaderField:@"module"]; NSURLConnection theConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self]; But it doesn't seem to work. I'm doing something wrong? is there a way to know if I'm using the wrong names for the parameters (as maybe it is "Location" or "LOCATION" or it doesn't matter?)? or a way to know which parameters is the function waiting for... Extra info: I don't have access to the source of the web service so I can't modify it. But I can access the WSDL. The person who made the function say is all there... but I can't make any sense of it .< Any help would be appreciated. :)

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How to unit test this simple ASP.NET MVC controller

- by Frank Schwieterman

Lets say I have a simple controller for ASP.NET MVC I want to test. I want to test that a controller action (Foo, in this case) simply returns a link to another action (Bar, in this case). How would you test this? (either the first or second link) My implementation has the same link twice. One passes the url throw ViewData[]. This seems more testable to me, as I can check the ViewData collection returned from Foo(). Even this way though, I don't know how to validate the url itself without making dependencies on routing. The controller: public class TestController : Controller { public ActionResult Foo() { ViewData["Link2"] = Url.Action("Bar"); return View("Foo"); } public ActionResult Bar() { return View("Bar"); } } the "Foo" view: <%@ Page Title="" Language="C#" Inherits="System.Web.Mvc.ViewPage" MasterPageFile="~/Views/Shared/Site.Master"%> <asp:Content ContentPlaceHolderID="MainContent" runat="server"> <%= Html.ActionLink("link 1", "Bar") %> <a href="<%= ViewData["Link2"]%>">link 2</a> </asp:Content>

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Javascript scope chain

- by Geromey

Hi, I am trying to optimize my program. I think I understand the basics of closure. I am confused about the scope chain though. I know that in general you want a low scope (to access variables quickly). Say I have the following object: var my_object = (function(){ //private variables var a_private = 0; return{ //public //public variables a_public : 1, //public methods some_public : function(){ debugger; alert(this.a_public); alert(a_private); }; }; })(); My understanding is that if I am in the some_public method I can access the private variables faster than the public ones. Is this correct? My confusion comes with the scope level of this. When the code is stopped at debugger, firebug shows the public variable inside the this keyword. The this word is not inside a scope level. How fast is accessing this? Right now I am storing any this.properties as another local variable to avoid accessing it multiple times. Thanks very much!

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Is it possible to search locally in jqGrid with treeGrid installed

- by Nehu

I am using jqGrid with treeGrid. I have added a filterToolbar. I would like to search locally instead of having a server call. The treegrid docs say that, "When we initialize the grid and the data is read, the datatype is automatically set to local." So, is it possible to implement local search with treeGrid. I tried the below configuration, but it is resulting in server calls. My Configuration is var grid = $("#grid").jqGrid({ treeGrid: true, treeGridModel: 'adjacency', ExpandColumn: 'businessAreaName', ExpandColClick : true, url:'agileProgramme/records.do', datatype: 'json', mtype: 'GET', colNames:['Id' , 'Business Area' , 'Investment' , 'Org' , 'Goal' ], colModel:[ /*00*/ {name:'agileProgrammeId',index:'agileProgrammeId', width:0, editable:false,hidden:true}, /*01*/ {name:'businessAreaName',index:'businessAreaName', width:160, editable:false}, /*02*/ {name:'programmeName',index:'programmeName', width:150, editable:false, classes:'link'}, /*03*/ {name:'org',index:'org', width:50, editable:false, classes:'orgHierarchy', sortable : false}, /*04*/ {name:'goal',index:'goal', width:70, editable:false} ], treeReader : { level_field: "level", parent_id_field: "parent", leaf_field: "leaf", expanded_field: "expanded" }, autowidth: true, height: 240, pager: '#pager', sortname: 'id', sortorder: "asc", toolbar:[true,"top"], caption:"TableGridDemo", emptyrecords: "Empty records", jsonReader : { root: "rows", page: "page", total: "total", records: "records", repeatitems: false, cell: "cell", id: "agileProgrammeId" } }); And to implement the search toolbar $('#grid').jqGrid('filterToolbar', {stringResult: true,searchOnEnter : true}); Would appreciate any help or any pointer on even if it is possible?

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Rewrite arrays using collections

- by owca

I have a task, which I was able to do with the use of simplest methods - arrays. Now I'd like to go further and redo it using some more complicated java features like collections, but I've never used anything more complicated than 2d matrix. What should I look at and how to start with it. Should Tower become a Collection ? And here's the task : We have two classes - Tower and Block. Towers are built from Blocks. Ande here's sample code for testing: Block k1=new Block("yellow",1,5,4); Block k2=new Block("blue",2,2,6); Block k3=new Block("green",3,4,2); Block k4=new Block("yellow",1,5,4); Tower tower=new Tower(); tower.add(k1,k2,k3); "Added 3 blocks." System.out.println(tower); "block: green, base: 4cm x 3cm, thicknes: 2 cm block: blue, base: 6cm x 2cm, thicknes: 2 cm block: yellow, base: 5cm x 4cm, thicknes: 1 cm" tower.add(k2); "Tower already contains this block." tower.add(k4); "Added 1 block." System.out.println(tower); "block: green, base: 4cm x 3cm, thicknes: 2 cm block: blue, base: 6cm x 2cm, thicknes: 2 cm block: yellow, base: 5cm x 4cm, thicknes: 1 cm block: yellow, base: 5cm x 4cm, thicknes: 1 cm" tower.delete(k1); "Deleted 1 block" tower.delete(k1); "Block not in tower" System.out.println(tower); "block: blue, base: 6cm x 2cm, thicknes: 2 cm block: yellow, base: 5cm x 4cm, thicknes: 1 cm block: yellow, base: 5cm x 4cm, thicknes: 1 cm" Let's say I will treat Tower as a collection of blocks. How to perform search for specific block among whole collection ? Or should I use other interface ?

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A copy of ApplicationController has been removed from the module tree but is still active

- by Matchu

Whenever two concurrent HTTP requests go to my Rails app, the second always returns the following error: A copy of ApplicationController has been removed from the module tree but is still active! From there it gives an unhelpful stack trace to the effect of "we went through the standard server stuff, ran your first before_filter on ApplicationController (and I checked; it's just whichever filter runs first)", then offers the following: /home/matchu/rails/torch/vendor/rails/activesupport/lib/active_support/dependencies.rb:414:in `load_missing_constant' /home/matchu/rails/torch/vendor/rails/activesupport/lib/active_support/dependencies.rb:96:in `const_missing' which I'm assuming is a generic response and doesn't really say much. Google seems to tell me that people developing Rails Engines will encounter this, but I don't do that. All I've done is upgrade my Rails app from 2.2 (2.1?) to 2.3. What are some possible causes for this error, and how can I go about tracking down what's really going on? I know this question is vague, so would any other information be helpful? More importantly: I tried doing a test run in a "production" environment just now, and the error doesn't seem to persist. Does this only affect development, then, and need I not worry too much?

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Multithreading and Interrupts

- by Nicholas Flynt

I'm doing some work on the input buffers for my kernel, and I had some questions. On Dual Core machines, I know that more than one "process" can be running simultaneously. What I don't know is how the OS and the individual programs work to protect collisions in data. There are two things I'd like to know on this topic: (1) Where do interrupts occur? Are they guaranteed to occur on one core and not the other, and could this be used to make sure that real-time operations on one core were not interrupted by, say, file IO which could be handled on the other core? (I'd logically assume that the interrupts would happen on the 1st core, but is that always true, and how would you tell? Or perhaps does each core have its own settings for interrupts? Wouldn't that lead to a scenario where each core could react simultaneously to the same interrupt, possibly in different ways?) (2) How does the dual core processor handle opcode memory collision? If one core is reading an address in memory at exactly the same time that another core is writing to that same address in memory, what happens? Is an exception thrown, or is a value read? (I'd assume the write would work either way.) If a value is read, is it guaranteed to be either the old or new value at the time of the collision? I understand that programs should ideally be written to avoid these kinds of complications, but the OS certainly can't expect that, and will need to be able to handle such events without choking on itself.

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Behavior of retained propertie while holder is retained

- by Aurélien Vallée

Hello everyone, I am a beginner ObjectiveC programmer, coming from the C++ world. I find it very difficult to understand the memory management offered by NSObject :/ Say I have the following class: @interface User : NSObject { NSString* name; } @property (nonatomic,retain) NSString* name; - (id) initWithName: (NSString*) theName; - (void) release; @end @implementation User @synthetise name - (id) initWithName: (NSString*) theName { if ( self = [super init] ) { [self setName:theName]; } return self; } - (void) release { [name release]; [super release]; } @end No considering the following code, I can't understand the retain count results: NSString* name = [[NSString alloc] initWithCString:/*C string from sqlite3*/]; // (1) name retainCount = 1 User* user = [[User alloc] initWithName:name]; // (2) name retainCount = 2 [whateverMutableArray addObject:user]; // (3) name retainCount = 2 [user release]; // (4) name retainCount = 1 [name release]; // (5) name retainCount = 0 At (4), the retain count of name decreased from 2 to 1. But that's not correct, there is still the instance of user inside the array that points to name ! The retain count of a variable should only decrease when the retain count of a referring variable is 0, that is, when it is dealloced, not released.

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Rails Polymorphic Association with multiple associations on the same model

- by Matt Rogish

My question is essentially the same as this one: http://stackoverflow.com/questions/1168047/polymorphic-association-with-multiple-associations-on-the-same-model However, the proposed/accepted solution does not work, as illustrated by a commenter later. I have a Photo class that is used all over my app. A post can have a single photo. However, I want to re-use the polymorphic relationship to add a secondary photo. Before: class Photo belongs_to :attachable, :polymorphic => true end class Post has_one :photo, :as => :attachable, :dependent => :destroy end Desired: class Photo belongs_to :attachable, :polymorphic => true end class Post has_one :photo, :as => :attachable, :dependent => :destroy has_one :secondary_photo, :as => :attachable, :dependent => :destroy end However, this fails as it cannot find the class "SecondaryPhoto". Based on what I could tell from that other thread, I'd want to do: has_one :secondary_photo, :as => :attachable, :class_name => "Photo", :dependent => :destroy Except calling Post#secondary_photo simply returns the same photo that is attached via the Photo association, e.g. Post#photo === Post#secondary_photo. Looking at the SQL, it does WHERE type = "Photo" instead of, say, "SecondaryPhoto" as I'd like... Thoughts? Thanks!

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Is an "infinite" iterator bad design?

- by Adamski

Is it generally considered bad practice to provide Iterator implementations that are "infinite"; i.e. where calls to hasNext() always(*) return true? Typically I'd say "yes" because the calling code could behave erratically, but in the below implementation hasNext() will return true unless the caller removes all elements from the List that the iterator was initialised with; i.e. there is a termination condition. Do you think this is a legitimate use of Iterator? It doesn't seem to violate the contract although I suppose one could argue it's unintuitive. public class CyclicIterator<T> implements Iterator<T> { private final List<T> l; private Iterator it; public CyclicIterator<T>(List<T> l) { this.l = l; this.it = l.iterator(); } public boolean hasNext() { return !l.isEmpty(); } public T next() { T ret; if (!hasNext()) { throw new NoSuchElementException(); } else if (it.hasNext()) { ret = it.next(); } else { it = l.iterator(); ret = it.next(); } return ret; } public void remove() { it.remove(); } }

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Using LINQ to SQL and chained Replace

- by White Dragon

I have a need to replace multiple strings with others in a query from p in dx.Table where p.Field.Replace("A", "a").Replace("B", "b").ToLower() = SomeVar select p Which provides a nice single SQL statement with the relevant REPLACE() sql commands. All good :) I need to do this in a few queries around the application... So i'm looking for some help in this regard; that will work as above as a single SQL hit/command on the server It seems from looking around i can't use RegEx as there is no SQL eq Being a LINQ newbie is there a nice way for me to do this? eg is it possible to get it as a IQueryable "var result" say and pass that to a function to add needed .Replace()'s and pass back? Can i get a quick example of how if so? EDIT: This seems to work! does it look like it would be a problem? var data = from p in dx.Videos select p; data = AddReplacements(data, checkMediaItem); theitem = data.FirstOrDefault(); ... public IQueryable<Video> AddReplacements(IQueryable<Video> DataSet, string checkMediaItem) { return DataSet.Where(p => p.Title.Replace(" ", "-").Replace("&", "-").Replace("?", "-") == checkMediaItem); }

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How can I get this dynamic WHERE statement in my LINQ-to-XML to work?

- by Edward Tanguay

In this question Jon Skeet offered a very interesting solution to making a LINQ-to-XML statement dynamic, but my knowledge of lambdas and delegates is not yet advanced enough to implement it: I've got it this far, but of course I get the error "smartForm does not exist in the current context": private void LoadWithId(int id) { XDocument xmlDoc = null; try { xmlDoc = XDocument.Load(FullXmlDataStorePathAndFileName); } catch (Exception ex) { throw new Exception(String.Format("Cannot load XML file: {0}", ex.Message)); } Func<XElement, bool> whereClause = (int)smartForm.Element("id") == id"; var smartForms = xmlDoc.Descendants("smartForm") .Where(whereClause) .Select(smartForm => new SmartForm { Id = (int)smartForm.Element("id"), WhenCreated = (DateTime)smartForm.Element("whenCreated"), ItemOwner = smartForm.Element("itemOwner").Value, PublishStatus = smartForm.Element("publishStatus").Value, CorrectionOfId = (int)smartForm.Element("correctionOfId"), IdCode = smartForm.Element("idCode").Value, Title = smartForm.Element("title").Value, Description = smartForm.Element("description").Value, LabelWidth = (int)smartForm.Element("labelWidth") }); foreach (SmartForm smartForm in smartForms) { _collection.Add(smartForm); } } Ideally I want to be able to just say: var smartForms = GetSmartForms(smartForm=> (int) smartForm.Element("DisplayOrder").Value > 50); I've got it this far, but I'm just not grokking the lambda magic, how do I do this? public List<SmartForm> GetSmartForms(XDocument xmlDoc, XElement whereClause) { var smartForms = xmlDoc.Descendants("smartForm") .Where(whereClause) .Select(smartForm => new SmartForm { Id = (int)smartForm.Element("id"), WhenCreated = (DateTime)smartForm.Element("whenCreated"), ItemOwner = smartForm.Element("itemOwner").Value, PublishStatus = smartForm.Element("publishStatus").Value, CorrectionOfId = (int)smartForm.Element("correctionOfId"), IdCode = smartForm.Element("idCode").Value, Title = smartForm.Element("title").Value, Description = smartForm.Element("description").Value, LabelWidth = (int)smartForm.Element("labelWidth") }); }

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