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• Explanation of `self` usage during dealloc?

  - by Greg

  I'm trying to lock down my understanding of proper memory management within Objective-C. I've gotten into the habit of explicitly declaring self.myProperty rather than just myProperty because I was encountering occasional scenarios where a property would not be set to the reference that I intended. Now, I'm reading Apple documentation on releasing IBOutlets, and they say that all outlets should be set to nil during dealloc. So, I put this in place as follows and experienced crashes as a result: - (void)dealloc { [self.dataModel close]; [self.dataModel release], self.dataModel = nil; [super dealloc]; } So, I tried taking out the "self" references, like so: - (void)dealloc { [dataModel close]; [dataModel release], dataModel = nil; [super dealloc]; } This second system seems to work as expected. However, it has me a bit confused. Why would self cause a crash in that case, when I thought self was a fairly benign reference more used as a formality than anything else? Also, if self is not appropriate in this case, then I have to ask: when should you include self references, and when should you not?

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• User defined literal arguments are not constexpr?

  - by Pubby

  I'm testing out user defined literals. I want to make _fac return the factorial of the number. Having it call a constexpr function works, however it doesn't let me do it with templates as the compiler complains that the arguments are not and cannot be constexpr. I'm confused by this - aren't literals constant expressions? The 5 in 5_fac is always a literal that can be evaluated during compile time, so why can't I use it as such? First method: constexpr int factorial_function(int x) { return (x > 0) ? x * factorial_function(x - 1) : 1; } constexpr int operator "" _fac(unsigned long long x) { return factorial_function(x); // this works } Second method: template <int N> struct factorial { static const unsigned int value = N * factorial<N - 1>::value; }; template <> struct factorial<0> { static const unsigned int value = 1; }; constexpr int operator "" _fac(unsigned long long x) { return factorial_template<x>::value; // doesn't work - x is not a constexpr }

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• A typical mysql query( how to use subquery column into main query)

  - by I Like PHP

  I HAVE TWO TABLES shown below table_joining id join_id(PK) transfer_id(FK) unit_id transfer_date joining_date 1 j_1 t_1 u_1 2010-06-05 2010-03-05 2 j_2 t_2 u_3 2010-05-10 2010-03-10 3 j_3 t_3 u_6 2010-04-10 2010-01-01 4 j_5 NULL u_3 NULL 2010-06-05 5 j_6 NULL u_4 NULL 2010-05-05 table_transfer id transfer_id(PK) pastUnitId futureUnitId effective_transfer_date 1 t_1 u_3 u_1 2010-06-05 2 t_2 u_6 u_1 2010-05-10 3 t_3 u_5 u_3 2010-04-10 now i want to know total employee detalis( using join_id) which are currently working on unit u_3 . means i want only join_id j_1 (has transfered but effective_transfer_date is future date, right now in u_3) j_2 ( tansfered and right now in `u_3` bcoz effective_transfer_date has been passed) j_6 ( right now in `u_3` and never transfered) what i need to take care of below steps( as far as i know ) <1> first need to check from table_joining whether transfer_id is NULL or not <2> if transfer_id= is NULL then see unit_id=u_3 where joining_date <=CURDATE() ( means that person already joined u_3) <3> if transfer_id is NOT NULL then go to table_transfer using transfer_id (foreign key reference) <4> now see the effective_transfer_date regrading that transfer_id whether effective_transfer_date<=CURDATE() <5> if transfer date has been passed(means transfer has been done) then return futureUnitID otherwise return pastUnitID i used two separate query but don't know how to join those query?? for step <1 ans <2 SELECT unit_id FROM table_joining WHERE joining_date<=CURDATE() AND transfer_id IS NULL AND unit_id='u_3' for step<5 SELECT IF(effective_transfer_date <= CURDATE(),futureUnitId,pastUnitId) AS currentUnitID FROM table_transfer // here how do we select only those rows which have currentUnitID='u_3' ?? please guide me the process?? i m just confused with JOINS. i think using LEFT JOIN can return the data i need, or if we use subquery value to main query? but i m not getting how to implement ...please help me. Thanks for helping me alwayz

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• Entity Framework and WCf

  - by Nihilist

  Hi I am little confused on designing WCf services with EF. When using WCf and EF, where do we draw this line on what properties to return and what not to with the entity. Here is my scenario I have User. Here are the relations. User [1 to many] Address, User [ 1 to many] Email, User [ 1 to many] Phone So now on the webform, on page1 I can edit user information. say I can edit few properties on the user entity and can also edit address, phone, email entities[ like add / delete and update any] On page2, i can only update user properties and nothing related to navigation properties [ address, email, phone]. So when I return the User Entity [ OR DTO] should i be returning the navigation properties too? Or should the client make multiple calls to get navigation properites. Also, how does it go with Save? Like should the client make multiple calls to save user and related entites or just one call to save the graph? Lets say, if I just have a Save(User user) [ where user has all the related entities too] both page1 and page2 will call save and pass me the user. but one page1 i will need a lot more information. but on page2 i just need the user primitive properties. So my question is, where do we draw this line, how do we design theses services ? Is the WCF operation designed on the page and the fields it has ? I am hoping i explained my problem well enough.

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• Are UTF16 (as used by for example wide-winapi functions) characters always 2 byte long?

  - by Cray

  Please clarify for me, how does UTF16 work? I am a little confused, considering these points: There is a static type in C++, WCHAR, which is 2 bytes long. (always 2 bytes long obvisouly) Most of msdn and some other documentation seem to have the assumptions that the characters are always 2 bytes long. This can just be my imagination, I can't come up with any particular examples, but it just seems that way. There are no "extra wide" functions or characters types widely used in C++ or windows, so I would assume that UTF16 is all that is ever needed. To my uncertain knowledge, unicode has a lot more characters than 65535, so they obvisouly don't have enough space in 2 bytes. UTF16 seems to be a bigger version of UTF8, and UTF8 characters can be of different lengths. So if a UTF16 character not always 2 bytes long, how long else could it be? 3 bytes? or only multiples of 2? And then for example if there is a winapi function that wants to know the size of a wide string in characters, and the string contains 2 characters which are each 4 bytes long, how is the size of that string in characters calculated? Is it 2 chars long or 4 chars long? (since it is 8 bytes long, and each WCHAR is 2 bytes)

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• What VC++ compiler/linker does when building a C++ project with Managed Extension

  - by ???

  The initial problem is that I tried to rebuild a C++ project with debug symbols and copied it to test machine, The output of the project is external COM server(.exe file). When calling the COM interface function, there's a RPC call failre: COMException(0x800706BE): The remote procedure call failed. According to the COM HRESULT design, if the FACILITY code is 7, it's actually a WIN32 error, and the win32 error code is 0x6BE, which is the above mentioned "remote procedure call failed". All I do is replace the COM server .exe file, the origin file works well. When I checked into the project, I found it's a C++ project with Managed Extension. When I checking the DLL with reflector, it shows there's 2 additional .NET assembly reference. Then I checked the project setting and found nothing about the extra 2 assembly reference. I turned on the show includes option of compiler and verbose library of linker, and try to analyze whether the assembly is indirectly referenced via .h file. I've collect all the .h file and grep all the files with '#using' '#import' and the assembly file itself. There really is a '#using ' in one of the .h file but not-relevant to the referenced assembly. And about the linked .lib library files, only one of the .lib file is a side-product of another managed-extension-enabled C++ project, all others are produced by a pure, traditional C++ project. For the managed-extension-enabled C++ project, I checked the output DLL assembly, it did NOT reference to the 2 assembly. I even try to capture the access of the additional assembly file via sysinternal's filemon and procmon, but the rebuild process does NOT access these file. I'm very confused about the compile and linking process model of a VC++/CLI project, where the additional assembly reference slipped into the final assembly? Thanks in advance for any of your help.

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• Is `List<Dog>` a subclass of `List<Animal>`? Why aren't Java's generics implicitly polymorphic?

  - by froadie

  I'm a bit confused about how Java generics handle inheritance / polymorphism. Assume the following hierarchy - Animal (Parent) Dog - Cat (Children) So suppose I have a method doSomething(List<Animal> animals). By all the rules of inheritance and polymorphism, I would assume that a List<Dog> is a List<Animal> and a List<Cat> is a List<Animal> - and so either one could be passed to this method. Not so. If I want to achieve this behavior, I have to explicitly tell the method to accept a list of any subset of Animal by saying doSomething(List<? extends Animal> animals). I understand that this is Java's behavior. My question is why? Why is polymorphism generally implicit, but when it comes to generics it must be specified?

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• Does it ever make sense to make a fundamental (non-pointer) parameter const?

  - by Scott Smith

  I recently had an exchange with another C++ developer about the following use of const: void Foo(const int bar); He felt that using const in this way was good practice. I argued that it does nothing for the caller of the function (since a copy of the argument was going to be passed, there is no additional guarantee of safety with regard to overwrite). In addition, doing this prevents the implementer of Foo from modifying their private copy of the argument. So, it both mandates and advertises an implementation detail. Not the end of the world, but certainly not something to be recommended as good practice. I'm curious as to what others think on this issue. Edit: OK, I didn't realize that const-ness of the arguments didn't factor into the signature of the function. So, it is possible to mark the arguments as const in the implementation (.cpp), and not in the header (.h) - and the compiler is fine with that. That being the case, I guess the policy should be the same for making local variables const. One could make the argument that having different looking signatures in the header and source file would confuse others (as it would have confused me). While I try to follow the Principle of Least Astonishment with whatever I write, I guess it's reasonable to expect developers to recognize this as legal and useful.

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• What does this structure actually do?

  - by LGTrader

  I found this structure code in a Julia Set example from a book on CUDA. I'm a newbie C programmer and cannot get my head around what it's doing, nor have I found the right thing to read on the web to clear it up. Here's the structure: struct cuComplex { float r; float i; cuComplex( float a, float b ) : r(a), i(b) {} float magnitude2( void ) { return r * r + i * i; } cuComplex operator*(const cuComplex& a) { return cuComplex(r*a.r - i*a.i, i*a.r + r*a.i); } cuComplex operator+(const cuComplex& a) { return cuComplex(r+a.r, i+a.i); } }; and it's called very simply like this: cuComplex c(-0.8, 0.156); cuComplex a(jx, jy); int i = 0; for (i=0; i<200; i++) { a = a * a + c; if (a.magnitude2() > 1000) return 0; } return 1; So, the code did what? Defined something of structure type 'cuComplex' giving the real and imaginary parts of a number. (-0.8 & 0.156) What is getting returned? (Or placed in the structure?) How do I work through the logic of the operator stuff in the struct to understand what is actually calculated and held there? I think that it's probably doing recursive calls back into the stucture float magnitude2 (void) { return return r * r + i * i; } probably calls the '*' operator for r and again for i, and then the results of those two operations call the '+' operator? Is this correct and what gets returned at each step? Just plain confused. Thanks!

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• How can I help fellow students struggling in programming classes?

  - by David Barry

  I'm a computer science student finishing up my second semester of programming classes. I've enjoyed them quite a bit, and learned a lot, but it seems other students are struggling with the concepts and assignments more than I am. When an assignment is due, the inevitable group email comes out the day or two before with people needing some help either with a specific part of the problem, or sometimes people just seem to have a hard time knowing where to start. I'd really like to be able to help out, but I have a hard time thinking of the right way to give them help without giving them the answer. When I'm having trouble understanding a concept, a code snippet can go along way to helping me, but at the same time if it makes a lot of sense, it can be difficult to think of another way to go about it. Plus the Academic Integrity section of each assignment is always looming overhead warning against sharing code with others. I've tried using pseudo code to help give others an idea on program flow, leaving them to figure out how to implement certain aspects of it, but I didn't get too much feedback and don't know how much it actually helped them out, or if it just confused them further. So I'm basically looking to see if anyone has experience with this, or good ways that I can help out other students to nudge them in the right direction or help them think about the problem in the right way.

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• What different terms mean the same thing (or don't, but people think they do)?

  - by Matthew Jones

  One of the pitfalls I run into on a daily basis is customers saying one thing while meaning another. Usually, this is just due to a miscommunication somewhere, but occasionally they are, in fact, saying the same thing I am just using a different term. For example, one of my customers the other day mentioned a feature he called, "find as you type." Being a little confused, I asked him what he meant, and he described the feature in Google where, once you start typing a search query, Google suggests other, popular queries that match the letters you have typed. Click! He meant AutoComplete! He was not wrong, it is just that I had never heard that term before. In the spirit of reducing confusion, what terms can you think of that are different but mean, essentially, the same thing? Also, what terms do people think mean the same thing, but don't. Please differentiate between the two. Please only one set of terms per answer, so we can vote on the best ones.

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• Why NOT use POST method here?

  - by Camran

  I have a classifieds website. In the main page (index) I have several form fields which the user may or may not fill in, in order to specify a detailed search of classifieds. Ex: Category: Cars Price from: 3000 Price to: 10000 Color: Red Area: California The forms' action is set to a php page: <form action='query_sql.php' method='post'> In query_sql.php I fetch the variables like this: category=$_POST['category']; etc etc... Then query MySql: $query="SELECT........WHERE category='$category' etc etc.... $results = mysql_query($query); Then I simply display the results of the query to the user by creating a table which is filled in dynamically depending on the results set. However, according to an answer by Col. Shrapnel in my previous Q I shouldn't use POST here: http://stackoverflow.com/questions/3004754/how-to-hide-url-from-users-when-submitting-this-form The reason I use post is simply to hide the "one-page-word-document" long URL in the browsers adress bar. I am very confused, is it okay to use POST or not? It is working fine both when I use GET or POST now... And it is already on a production server... Btw, in the linked question, I wasn't referring to make URL invisible (or hide it) I just wanted it too look better (which I have accomplished with mod_rewrite). UPDATE: If I use GET, then how should I make the url better looking (beautiful)? Check this previous Q out: http://stackoverflow.com/questions/3000524/how-to-make-this-very-long-url-appear-short

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• Apache redirection problem!!!!

  - by vikas

  Hi guys, I am setting up a pre-built website built in php. The site was actually hosted on the linux server. Now I am trying to set it up on a Window machine with WAMP server. In this website almost every page request passes through a particular file called redirect(which is basically a php file without extension). Now the problem is that when I inspected the configuration(httpd.conf, apache.conf,.htaccess, vhost.conf etc) of the apache server on the linux machine, I nowhere found the redirect rules for doing so. Neither mod_rewrite nor mod_alias rules for this redirection were found there. But is still redirects the request properly. I also noticed that Zend Framework library is there in the exact same directory where the redirect file is. This library is included in the include_path in php.ini. However, the web site is still not developed using Zend MVC and I have seen NO proof of ZEND being used there. So I am really confused how this redirection is working there? I am unable to set up this on window machine without rewrite rules of mod_rewrite or mod_alias. Do you guys know any alternative of both the said modules for redirection? I know the site is really weird, but i have to set it up. :) Thanks in advance for your help.

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• SSL + Jquery + Ajax

  - by chobo2

  Hi I starting too look at a bit of security into my site. My site I would consider a very low security risk as it has really no personal information from the user other than email. However the security risk will go up a bit as I am partnering with a company and the initial password for this companies users will be the same password they use essentially to get onto the network and every piece of software. So I have up my security( what is fine by me...I wanted to get around to this anyways). So one of my security concerns is this. A user logs in. form submit(non ajax is done). Password is hashed & Salted and compared to one in the database. Reject or let them proceed. So this uses no jquery or ajax but is just asp.net mvc and C#. Still if my understanding is right the password is sent in clear text. So if a use SSL and I would not need to worry about that is this correct? If that is true is that all I need? Second the user can change their password at anytime. This is done through ajax. So when the password is sent it is sent in clear text( and I can verify this by looking at firebug). So if I have SSL enabled on this page is that all I need or do I need to do more? So I am just kinda confused of what I need to make the password being sent to the server(both ajax and full post ways secure). I am not sure if I need to do more then SSL or if that is enough and if it is not enough what is the next layer of security?

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• Copy and paste between sheets in a workbook with VBA code

  - by Hannah

  Trying to write a macro in VBA for Excel to look at the value in a certain column from each row of data in a list and if that value is "yes" then it copies and pastes the entire row onto a different sheet in the same workbook. Let's name the two sheets "Data" and "Final". I want to have the sheets referenced so it does not matter which sheet I have open when it runs the code. I was going to use a Do loop to cycle through the rows on the one data sheet until it finds there are no more entries, and if statements to check the values. I am confused about how to switch from one sheet to the next. How do I specifically reference cells in different sheets? Here is the pseudocode I had in mind: Do while DataCells(x,1).Value <> " " for each DataCells(x,1).Value="NO" if DataCells(x,2).Value > DataCells(x,3).Value or _ DataCells(x,4).Value < DataCells(x,5).Value 'Copy and paste/insert row x from Data to Final sheet adding a new 'row for each qualifying row else x=x+1 end else if DataCells(x,1).Value="YES" Loop 'copy and paste entire row to a third sheet 'continue this cycle until all rows in the data sheet are examined

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• confusion about using types instead of gtts in oracle

  - by Omnipresent

  I am trying to convert queries like below to types so that I won't have to use GTT: insert into my_gtt_table_1 (house, lname, fname, MI, fullname, dob) (select house, lname, fname, MI, fullname, dob from (select 'REG' house, mbr_last_name lname, mbr_first_name fname, mbr_mi MI, mbr_first_name || mbr_mi || mbr_last_name fullname, mbr_dob dob from table_1 a, table_b where a.head = b.head and mbr_number = '01' and mbr_last_name = v_last_name) c above is just a sample but complex queries are bigger than this. the above is inside a stored procedure. So to avoid the gtt (my_gtt_table_1). I did the following: create or replace type lname_row as object ( house varchar2(30) lname varchar2(30), fname varchar2(30), MI char(1), fullname VARCHAR2(63), dob DATE ) create or replace type lname_exact as table of lname_row Now in the SP: type lname_exact is table of <what_table_should_i_put_here>%rowtype; tab_a_recs lname_exact; In the above I am not sure what table to put as my query has nested subqueries. query in the SP: (I am trying this for sample purpose to see if it works) select lname_row('', '', '', '', '', '', sysdate) bulk collect into tab_a_recs from table_1; I am getting errors like : ORA-00913: too many values I am really confused and stuck with this :(

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• What does it mean to say "Instance variables are not over-rided" in java?

  - by Ankit

  I am aware of the concept called field hiding in java. But still I am having a confusion in relation to instance variable being not over-ridden. According to my present knowledge, overriding a method of super-class means that the JVM will call the sub-class's over-ridden method though the super-class's method is available to the sub-class. And I read the similar thing for field hiding via the link:- Hiding Fields So, in any case we are over-ridding the instance if we change the values of the inherited instance variable in the sub-class. I am confused please help. I am using the following super-class:- public class Animal{ File picture; String food; int hunger; int width, height; int xcoord, ycoord; public void makeNoise(){ ......... } public void eat(){ ............. } public void sleep(){ .......... } public void roam(){ ............. } } It has sub-classes like Tiger, cat, dog,hippo etc. The sub-classes over-ride the makeNoise(), eat and roam() method. But each sub-class also uses a different set of values for instance variables. So as per my confusion, I am kind-of overriding all the instance variables and 3 methods of the super-class Animal; and I still have the super-class instance variables available to the sub-class with the use of the super keyword.

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• What is the difference between Inversion of Control and Dependency injection in C++?

  - by rlbond

  I've been reading recently about DI and IoC in C++. I am a little confused (even after reading related questions here on SO) and was hoping for some clarification. It seems to me that being familiar with the STL and Boost leads to use of dependency injection quite a bit. For example, let's say I made a function that found the mean of a range of numbers: template <typename Iter> double mean(Iter first, Iter last) { double sum = 0; size_t number = 0; while (first != last) { sum += *(first++); ++number; } return sum/number; }; Is this dependency injection? Inversion of control? Neither? Let's look at another example. We have a class: class Dice { public: typedef boost::mt19937 Engine; Dice(int num_dice, Engine& rng) : n_(num_dice), eng_(rng) {} int roll() { int sum = 0; for (int i = 0; i < num_dice; ++i) sum += boost::uniform_int<>(1,6)(eng_); return sum; } private: Engine& eng_; int n_; }; This seems like dependency injection. But is it inversion of control? Also, if I'm missing something, can someone help me out?

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• how to get the latitude or longitude in HTML 5

  - by steven spielberg

  few month ago i write something to get the latitude or longitude from google API. latter i get the database from drupal for latitude or longitude to most of city in worlds. but the problem is that the same city name can be found two or more times in a area. like Firozabad in India and bangladesh both. Agra in UP and agar in Rajasthan. means the confusion in name by user if they found two city by same name they are confused. i hear that HTML 5 support latitude or longitude of the visiter but i need latitude or longitude where they are born or city they want to use to fill a form. how i can get the latitude or longtiude from API like google and some other. the process is that: user put the location in textbox for getting their latitude or longitude. for right thing i want to show them all location [if same thing found more then one]. they can choose the right location and after click they can get the lati and langitude. how i can do this using any API.

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• What *is* an IPM.DistList?

  - by Jeremy

  I'm trying to get the recipient addresses within an IPM.DistList that is stored in a public folder (of type contacts) in Exchange 2003. The typeName of the object (once I get hold of it) is a Message (with a parent object being a Messages collection) and the messageType is "IPM.DistList". I can find all sorts of things about IPM.DistListItems, which you would think an IPM.DistList would contain, but there apparently isn't any documentation on the DistList (that I can find) and DistListItems documentation lists no parent possibilities in MSDN. I'll state it another way in case I've left you confused: We have an Exchange 2003 info store with Public Folders. Within those Public Folders is a [sub]folder (that holds items of type "Contact") that has a bunch of distribution lists (IPM.DistList's) that have contact entries, members of the list essentially. I need to get the addresses of the members of the lists in the Public Folder sub-folder using any VB language, because the company I work for hired me as a VB guy and expects me to write VB solutions, even though I could do it in C++... alas, I digress. VB is the language I'm supposed to figure this out in. (.net, script, vba, vb6, it doesn't matter which one. Yes, I know vb.net is not really related to those that came before, but they don't know that.) Anyone ran into anything like this? Am I just not finding the IPM.DistList documentation but it does actually exist somewhere? This isn't a Message.MAPIOBJECT (iUnknown) problem is it? Thanks.... Jeremy

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• What are the differences between mapping,binding and parsing?

  - by sfrj

  I am starting to learn web-services in java EE6. I did web development before, but never nothing related to web services. All is new to me and the books and the tutorials i find in the web are to technical. I started learning about .xsd schemas and also .xml. In that topic i feel confident, i understand what are the schemas used for and what validation means. Now my next step is learning about JAX-B(Java Api for XML Binding). I rode some about it and i did also some practice in my IDE. But i have lots of basic doubts, that make me stuck and cannot feel confident to continue to the next topic. Ill appreciate a lot if someone could explain me well my doubts: What does it mean mapping and what is a mapping tool? What does it mean binding and what is a binding tool? What does it mean parsing and what is a parsing tool? How is JAX-B related to mapping,binding and parsing? I am seeking for a good answer built by you, not just a copy paste from google(Ive already been online a few hours and only got confused).

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• Foreign key relationships in Entity Framework

  - by Anders Svensson

  I'm trying to add an object created from Entity Data Model classes. I have a table called Users, which has turned into a User EDM class. And I also have a table Pages, which has become a Page EDM class. These tables have a foreign key relationship, so that each page is associated with many users. Now I want to be able to add a page, but I can't get how to do it. I get a nullreference exception on Users below. I'm still rather confused by all this, so I'm sure it's a simple error, but I just can't see how to do it. Also, by the way, the compiler requires that I set PageID in the object initializer, even though this field is set to be an automatic id in the table. Am I doing it right just setting it to 0, expecting it to be updated automatically in the table when saved, or how should I do that? Any help appreciated! The method in question: private Page GetPage(User currentUser) { string url = _request.ServerVariables["url"].ToLower(); var userPages = from p in _context.PageSet where p.Users.UserID == currentUser.UserID select p; var existingPage = userPages.FirstOrDefault(e => e.Url == url); //Could be combined with above, but hard to read? if (existingPage != null) return existingPage; Page page = new Page() { Count = 0, Url = _request.ServerVariables["url"].ToLower(), PageID = 0, //Only initial value, changed later? }; _context.AddToPageSet(page); page.Users.UserID = currentUser.UserID; //Here's the problem... return page; }

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• How do I implement aasm in Rails 3 for what I want it to do?

  - by marcamillion

  I am a Rails n00b and have been advised that in order for me to keep track of the status of my user's accounts (i.e. paid, unpaid (and therefore disabled), free trial, etc.) I should use an 'AASM' gem. So I found one that seems to be the most popular: https://github.com/rubyist/aasm But the instructions are pretty vague. I have a Users model and a Plan model. User's model manages everything you might expect (username, password, first name, etc.). Plan model manages the subscription plan that users should be assigned to (with the restrictions). So I am trying to figure out how to use the AASM gem to do what I want to do, but no clue where to start. Do I create a new model ? Then do I setup a relationship between my User model and the model for AASM ? How do I setup a relationship? As in, a user 'has_many' states ? That doesn't seem to make much sense to me. Any guidance would be really appreciated. Thanks. Edit: If anyone else is confused by AASMs like myself, here is a nice explanation of their function in Rails by the fine folks at Envy Labs: http://blog.envylabs.com/2009/08/the-rails-state-machine/ Edit2: How does this look: include AASM aasm_column :current_state aasm_state :paid aasm_state :free_trial aasm_state :disabled #this is for accounts that have exceed free trial and have not paid #aasm_state :free_acct aasm_event :pay do transitions :to => :paid, :from => [:free_trial, :disabled] transitions :to => :disabled, :from => [:free_trial, :paid] end

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• In which domains are message oriented middleware like AMQP useful?

  - by cocotwo

  What problem do MOM (Message Oriented Middleware) solve? Scalability? Integration? In which domain are they typically used and in which domains are they typically not used? For example, say, is Google using such solution for it's main search engine or to power GMail? What about big websites like Walmart, eBay, FedEx (pretty much a Java shop) and buy.com (pretty much an MS shop)? Does MOM solve a need there? Does it make any sense when you're writing a Webapp where you control the server-side and have an homogenous environment (say tens of Amazon EC2 instances all running Linux + Java JVMs) there and where the clients are, well, Web browsers? Does it make sense for desktop apps that need to communicate with a server? Or is it 'only' for big enterprise stuff where you typically have a happy mix of countless of different systems that needs to communicate in a way or another? I'm a bit confused as to what they're useful for and I think that with example of where they're appropriate and where they're not appropriate I could better understand their use.

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• How do I handle the messages for a simple web-based live chat, on the server side?

  - by Carson Myers

  I'm building a simple live chat into a web application running on Django, but one thing I'm confused about is how I should store the messages between users. The chat will support multiple users, and a chat "session" is composed of users connected to one user that is the "host." The application is a sort of online document collaboration thing, so user X has a document, and users Y and Z would connect to user X to talk about the document, and that would be one chat session. If user Y disconnected for five minutes, and then signed back in and reconnected to user X, he should not get any of the messages shared between users X and Z while he was away. if users X, Y, and Z can have a chat session about user X's document, then users X and Y can connect to a simultaneous, but separate discussion about user Z's document. How should I handle this? Should I keep each message in the database? Each message would have an owner user and a target user (the host), and a separate table would be used to connect users with messages (which messages are visible to what users). Or should I store each session as an HTML file on the server, which messages get appended to? The problem is, I can't just send messages directly between clients. They have to be sent to the server in a POST request, and then each client has to periodically check for the messages in a GET request. Except I can't just have each message cleared after a client fetches it, because there could be multiple clients. How should I set this up? Any suggestions?

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