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  • What is the max LINQ Expression Trees can do?

    - by yeeen
    What is the maximun that LINQ expression Tree can do? Can it define a class? How about a method, with all the declared name, modifiers, parametertype and return type? Must the program always define the tree himself? Is it possible to generate the tree from a given C# file? Where can I get resources to learn about writing basic to advanced Expression Tree and Expression Tree Visitor? (articles and videos will be great) Thanks for those who are able to help...

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  • Would this constructor be acceptable practice?

    - by Robb
    Let's assume I have a c++ class that have properly implemented a copy constructor and an overloaded = operator. By properly implemented I mean they are working and perform a deep copy: Class1::Class1(const Class1 &class1) { // Perform copy } Class1& Class1::operator=(const Class1 *class1) { // perform copy return *this; } Now lets say I have this constructor as well: Class1::Class1(Class1 *class1) { *this = *class1; } My question is would the above constructor be acceptable practice? This is code that i've inherited and maintaining.

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  • What is the MVC version of this code?

    - by Ian Boyd
    i'm trying to wrap my head around how to enterprise up my code: taking a simple routine and splitting it up into 5 or 6 methods in 3 or 4 classes. i quickly came up three simple examples of code how i currently write it. Could someone please convert these into an MVC/MVP obfuscated version? Example 1: The last name is mandatory. Color the text box red if nothing is entered. Color it green if stuff is entered: private void txtLastname_TextChanged(object sender, EventArgs e) { //Lastname mandatory. //Color pinkish if nothing entered. Greenish if entered. if (txtLastname.Text.Trim() == "") { //Lastname is required, color pinkish txtLastname.BackColor = ControlBad; } else { //Lastname entered, remove the coloring txtLastname.BackColor = ControlGood; } } Example 2: The first name is optional, but try to get it. We'll add a bluish tint to this "try to get" field: private void txtFirstname_TextChanged(object sender, EventArgs e) { //Firstname can be blank. //Hint them that they should *try* to get it with a bluish color. //If they do enter stuff: it better be not all spaces. if (txtFirstname.Text == "") { //Nothing there, hint it blue txtFirstname.BackColor = ControlRequired; } else if (txtFirstname.Text.Trim() == "") { //They entered spaces - bad user! txtFirstname.BackColor = ControlBad; } else { //Entered stuff, remove coloring txtFirstname.BackColor = SystemColors.Window; } } Example 3 The age is totally optional. If an age is entered, it better be valid: private void txtAge_TextChanged(object sender, EventArgs e) { //Age is optional, but if entered it better be valid int nAge = 0; if (Int32.TryParse(txtAge.Text, out nAge)) { //Valid integer entered if (nAge < 0) { //Negative age? i don't think so txtAge.BackColor = ControlBad; } else { //Valid age entered, remove coloring txtAge.BackColor = SystemColors.Window; } } else { //Whatever is in there: it's *not* a valid integer, if (txtAge.Text == "") { //Blank is okay txtAge.BackColor = SystemColors.Window; } else { //Not a valid age, bad user txtAge.BackColor = ControlBad; } } } Every time i see MVC code, it looks almost like random splitting of code into different methods, classes, and files. i've not been able to determine a reason or pattern to their madness. Without any understanding of they why it's being one some way, it makes no sense. And using the words model, view, controller and presenter, like i'm supposed to know what that means, doesn't help. The model is your data. The view shows data on screen. The controller is used to carry out the users actions And oranges taste orangy. Here's my attempt at splitting things up in order to make the code more difficult to follow. Is this anywhere close to MVC? private void txtFirstname_TextChanged(object sender, EventArgs e) { FirstnameTextChangedHandler(sender, e); } private void FirstnameTextChangedHandler(sender, e) { string firstname = GetFirstname(); Color firstnameTextBoxColor = GetFirstnameTextBoxColor(firstname); SetFirstNameTextBoxColor(firstnameTextBoxColor); } private string GetFirstname() { return txtFirstname.Text; } private Color GetFirstnameTextBoxColor(string firstname) { //Firstname can be blank. //Hint them that they should *try* to get it with a bluish color. //If they do enter stuff: it better be not all spaces. if (firstname == "") { //Nothing there, hint it blue return GetControlRequiredColor(); } else if (firstname.Trim() == "") { //They entered spaces - bad user! return GetControlBadColor(); } else { //Entered stuff, remove coloring return GetControlDefaultColor(); } } private Color GetControlRequiredColor() { return ControlRequired; } private Color GetControlBadColor() { return ControlBad; } private Color GetControlGoodColor() { return ControlGood; } //am i doin it rite i've obfuscated the code, but it's still altogether. The next step in the MVC obfuscation, i gather, is to hide the code in 3 or 4 different files. It's that next step that i don't understand. What is the logical separation of which functions are moved into what other classes? Can someone translate my 3 simple examples above into full fledged MVC obfuscation? Edit: Not ASP/ASP.NET/Online. Pretend it's on a desktop, handheld, surface, kiosk. And pretend it's language agnostic.

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  • Voting Script, Possibility of Simplifying Database Queries

    - by Sev
    I have a voting script which stores the post_id and the user_id in a table, to determine whether a particular user has already voted on a post and disallow them in the future. To do that, I am doing the following 3 queries. SELECT user_id, post_id from votes_table where postid=? AND user_id=? If that returns no rows, then: UPDATE post_table set votecount = votecount-1 where post_id = ? Then SELECT votecount from post where post_id=? To display the new votecount on the web page Any better way to do this? 3 queries are seriously slowing down the user's voting experience Edit In the votes table, vote_id is a primary key In the post table, post_id is a primary key. Any other suggestions to speed things up?

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  • How to choose between UUIDs, autoincrement/sequence keys and sequence tables for database primary keys?

    - by Tim
    I'm looking at the pros and cons of these three primary methods of coming up with primary keys for database rows. So assuming I am using a database that supports more than one of these methods, is there a simple heuristic to determine what the best option would be for me? How do considerations such a distributed/multiple masters, performance requirements, ORM use, security and testing have on the choice? Any unexpected drawbacks that one might run into?

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  • Seeking free ODBC database optimization tool for non-experts

    - by mawg
    I'm a database n00b and am reading as many books as I can. I have been given responsibility for an ODBC tool where the databases were designed by a hardware engineer with some VB experience - which made him a s/w guru in the small firm at that time. Things are running slowly and I suspect that the db could have been designed better. I hope to learn enough to use Explain/Describe, etc maybe add some indices, but, in the meantime, is there any free for commercial use tool which can examine an ODBC database and suggest improvements. I'm just talking about db schema here, but maybe I should also be looking at optimizing Selects with Joins? Is there a tool for that? ODBC compliant.

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  • designing database tables using JDBC

    - by Noona
    I am creating a users table using JDBC and mysql, each user has a permissions list that comprises Integer values, I am wondering if I should use an array for storing these values and then have only 1 record for this user in the table, or simply create a new table that comprises 2 columns: user ID and permissions, and then have multiple records for each user that specify the user name in one columns and one permission value in the second column, the second option seems to be redundant since a permission value is a simple object that isn't associated with any other objects (like a student and courses list for example, because the course is associated with many other objects, like grade, teacher, etc, so in this case it is natural to have multiple records), but the first one seems to be a bit unnatural to me, so if someone has experience with these things and direct me? thanks

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  • Command Query Separation validating for retries

    - by Neil Barnwell
    So I'm comfortable with the basic concept of CQS, where you might have a command that writes to one database, and that updates the query database that you read from. However, consider the scenario where you are entering data, and want to prevent duplicates. Using new employee data entry an employee register as an example, working through a pile of application forms to key in the new employees' details: Take top sheet. Key in employee name and unique payroll number to UI. Submit. Put paper in "completed pile". Repeat. How would you now prevent the user from keying in the same payroll number again, say for instance if they get distracted and can't remember whether they've keyed one in already and the "message" hasn't got all the way back to the query db for the user to search?

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  • What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

    - by fabrizioM
    I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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  • C++ Array vs vector

    - by blue_river
    when using C++ vector, time spent is 718 milliseconds, while when I use Array, time is almost 0 milliseconds. Why so much performance difference? int _tmain(int argc, _TCHAR* argv[]) { const int size = 10000; clock_t start, end; start = clock(); vector<int> v(size*size); for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { v[i*size+j] = 1; } } end = clock(); cout<< (end - start) <<" milliseconds."<<endl; // 718 milliseconds int f = 0; start = clock(); int arr[size*size]; for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { arr[i*size+j] = 1; } } end = clock(); cout<< ( end - start) <<" milliseconds."<<endl; // 0 milliseconds return 0; }

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  • How to intercept an Exit event for a Windows Form in VB?

    - by Dooms101
    When a user clicks on the little red "x" a.k.a. the form close button on the form command bar, what even is activated besides FormClosed() I know FormClosing() is called, but I cannot really stop the form from closing after my code is run. I want to be able to show a messagebox that asks if the user wants to exit the form or not. Obviously if they click no, I want the form to stay open, how would I do this?

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  • Unable to find the cause of an annoying content gap in my HTML/CSS?

    - by user1472747
    I'm quite new to CSS / HTML, and can't find the cause of this little bugger. I want it gone, so that the banner and the nav bar touch each other. Any help is greatly appreciated!! Here is the code for the site. I took out some of the irrelevant code. <!DOCTYPE html> <html> <!-- *****CSS CODE START*****--> <style type="text/css"> #container { margin: 0 auto; width: 900px; background: #fff; } #header { margin-top: 0px; } #header h1 { margin: 0; } #navigation { float: left; width: 900px; background: #333; } #navigation ul { margin: 0; padding: 0; } #navigation ul li { list-style-type: none; display: inline; } #navigation li a { display: block; float: left; padding: 5px 10px; color: #fff; text-decoration: none; border-right: 1px solid #fff; } #navigation li a:hover { background: #383; } #content-container { float: left; width: 900px; background: #fff url(/wp-content/uploads/layout-two-fixed-background.gif) repeat-y 100% 0; } #content { clear: left; float: left; width: 619px; height: 720px; padding: 10px 0; margin: 0 0 0 0px; display: inline; overflow: auto; } #content h2 { margin: 0; color: #003D5D; padding:10px; } #contentBody { padding:10px; font-size:22px; } #aside { float: right; width: 280px; padding: 20px 0; margin: 0 0px 0 0; display: inline; background: #cccccc; height: 700px; border-left: 1px solid #333 ; } #aside h3 { margin: 0 20px; color: #003D5D; font-family: Times New Roman; } #asideText { margin: 0 20px; font-family: Times New Roman;} #footer { clear: both; background: #ccc; text-align: right; padding: 5px; height: 1%; border-top: 1px solid #333 ; } </style> <!-- *****CSS CODE END***** --> <!-- *****HTML CODE START***** --> <body> <div id="container"> <div id="header"> <img src = file:///Users/jduffy/Desktop/projectSite/banner1.jpg> </img> </div> <div id="navigation"> <ul> <li><a href="file:///Users/jduffy/Desktop/projectSite/home">Home</a></li> <li><a href="file:///Users/jduffy/Desktop/projectSite/theProject">The Project</a></li> <li><a href="file:///Users/jduffy/Desktop/projectSite/Pictures">Pictures</a></li> <li><a href="file:///Users/jduffy/Desktop/projectSite/Contact">Contact us</a></li> </ul> </div> <div id="content-container"> <div id="content"> <h2> Page heading </h2> <div id="contentBody"> <p> home pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome page home pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome page home pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome pagehome page </p> <p> test2 </p> <p> test3 </p> </div> </div> <div id="aside"> <div id="asideHeading"> <h3> Aside Heading </h3> </div> <div id="asideText"> <p> test5 </p> </div> </div> <div id="footer"> <text id="footerDate">0</text> </div> </div> </div> </body> <!-- *****HTML CODE END***** --> </html> <!-- *****JavaScript CODE START***** --> <script type="text/javascript"> /*date*/ var today = new Date(); document.getElementById("footerDate").innerHTML = today; </script> <!-- *****JavaScript CODE END***** -->

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  • How to evade writing a lot of repetitive code when mapping?

    - by JPCF
    I have a data access layer (DAL) using Entity Framework, and I want to use Automapper to communicate with upper layers. I will have to map data transfer objects (DTOs) to entities as the first operation on every method, process my inputs, then proceed to map from entities to DTOs. What would you do to skip writing this code? As an example, see this: //This is a common method in my DAL public CarDTO getCarByOwnerAndCreditStatus(OwnerDTO ownerDto, CreditDto creditDto) { //I want to automatize this code on all methods similar to this Mapper.CreateMap<OwnerDTO,Owner>(); Mapper.CreateMap<CreditDTO,Credit>(); Owner owner = Mapper.map(ownerDto); Owner credit = Mapper.map(creditDto) //... Some code processing the mapped DTOs //I want to automatize this code on all methods similar to this Mapper.CreateMap<Car,CarDTO>(); Car car = Mapper.map(ownedCar); return car; }

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  • SQL 2008 Select Top 1000 and update the selected database drop-down

    - by CWinKY
    When you right click and do a Select top 1000 rows from a table in sql 2008, it opens a tab and writes the sql and then executes it. This is okay, however I'll erase the sql and use the same tab often to do other sql statements. What annoys me is that I have to go to the database drop-down at the top of the window and change it to the current database I'm in because it says Master. How can I make sql 2008 update the selected database for this tab automatically when I right click a table and do select top 1000? On a side note, can I automatically hide the select statement that it generates and just show grid of results?

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  • How would you structure your entity model for storing arbitrary key/value data with different data t

    - by Nathan Ridley
    I keep coming across scenarios where it will be useful to store a set of arbitrary data in a table using a per-row key/value model, rather than a rigid column/field model. The problem is, I want to store the values with their correct data type rather than converting everything to a string. This means I have to choose either a single table with multiple nullable columns, one for each data type, or a set of value tables, one for each data type. I'm also unsure as to whether I should use full third normal form and separate the keys into a separate table, referencing them via a foreign key from the value table(s), or if it would be better to keep things simple and store the string keys in the value table(s) and accept the duplication of strings. Old/bad: This solution makes adding additional values a pain in a fluid environment because the table needs to be modified regularly. MyTable ============================ ID Key1 Key2 Key3 int int string date ---------------------------- 1 Value1 Value2 Value3 2 Value4 Value5 Value6 Single Table Solution This solution allows simplicity via a single table. The querying code still needs to check for nulls to determine which data type the field is storing. A check constraint is probably also required to ensure only one of the value fields contains non-nulll data. DataValues ============================================================= ID RecordID Key IntValue StringValue DateValue int int string int string date ------------------------------------------------------------- 1 1 Key1 Value1 NULL NULL 2 1 Key2 NULL Value2 NULL 3 1 Key3 NULL NULL Value3 4 2 Key1 Value4 NULL NULL 5 2 Key2 NULL Value5 NULL 6 2 Key3 NULL NULL Value6 Multiple-Table Solution This solution allows for more concise purposing of each table, though the code needs to know the data type in advance as it needs to query a different table for each data type. Indexing is probably simpler and more efficient because there are less columns that need indexing. IntegerValues =============================== ID RecordID Key Value int int string int ------------------------------- 1 1 Key1 Value1 2 2 Key1 Value4 StringValues =============================== ID RecordID Key Value int int string string ------------------------------- 1 1 Key2 Value2 2 2 Key2 Value5 DateValues =============================== ID RecordID Key Value int int string date ------------------------------- 1 1 Key3 Value3 2 2 Key3 Value6 How do you approach this problem? Which solution is better? Also, should the key column be separated into a separate table and referenced via a foreign key or be should it be kept in the value table and bulk updated if for some reason the key name changes?

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  • Debugging instance of another thread altering my data

    - by Mick
    I have a huge global array of structures. Some regions of the array are tied to individual threads and those threads can modify their regions of the array without having to use critical sections. But there is one special region of the array which all threads may have access to. The code that accesses these parts of the array needs to carefully use critical sections (each array element has its own critical section) to prevent any possibility of two threads writing to the structure simultaneously. Now I have a mysterious bug I am trying to chase, it is occurring unpredictably and very infrequently. It seems that one of the structures is being filled with some incorrect number. One obvious explanation is that another thread has accidentally been allowed to set this number when it should be excluded from doing so. Unfortunately it seems close to impossible to track this bug. The array element in which the bad data appears is different each time. What I would love to be able to do is set some kind of trap for the bug as follows: I would enter a critical section for array element N, then I know that no other thread should be able to touch the data, then (until I exit the critical section) set some kind of flag to a debugging tool saying "if any other thread attempts to change the data here please break and show me the offending patch of source code"... but I suspect no such tool exists... or does it? Or is there some completely different debugging methodology that I should be employing.

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  • Should I be using the command pattern? Seems like a lot of work...

    - by Fedor
    My Room class has a lot of methods I used before I decided to use the command pattern. Previously, I was invoking a lot of commands and now it seems I have to make a method in my roomParser class for every method. If I wanted to invoke say, setHotelCode I would have to create a method in roomParser that iterates through and invokes the method. Is this the way I should be using the command pattern? <?php interface Parseable { public function parse( $arr, $dept ); } class Room implements Parseable { protected $_adults; protected $_kids; protected $_startDate; protected $_endDate; protected $_hotelCode; protected $_sessionNs; protected $_minRate; protected $_maxRate; protected $_groupCode; protected $_rateCode; protected $_promoCode; protected $_confCode; protected $_currency = 'USD'; protected $_soapAction; protected $_soapHeaders; protected $_soapServer; protected $_responseXml; protected $_requestXml; public function __construct( $startdate,$enddate,$rooms=1,$adults=2,$kids=0 ) { $this->setNamespace(SESSION_NAME); $this->verifyDates( $startdate, $enddate ); $this->_rooms= $rooms; $this->_adults= $adults; $this->_kids= $kids; $this->setSoapAction(); $this->setRates(); } public function parse( $arr, $dept ) { $this->_price = $arr * $dept * rand(); return $this; } public function setNamespace( $namespace ) { $this->_sessionNs = $namespace; } private function verifyDates( $startdate, $enddate ) {} public function setSoapAction( $str= 'CheckAvailability' ) { $this->_soapAction = $str; } public function setRates( $rates='' ) { } public function setHotelCode($code ) { $this->_hotelCode = $code; } private function getSoapHeader() { return '<?xml version="1.0" encoding="utf-8"?> <soap:Header> </soap:Header>'; } private function getSoapFooter() { return '</soap:Envelope>'; } private function getSource() { return '<POS> <Source><RequestorId ID="" ID_Context="" /></Source> </POS>'; } function requestXml() { $this->_requestXml = $this->getSoapHeader(); $this->_requestXml .='<soap:Body></soap:Body>'; return $this->_requestXml; } private function setSoapHeaders ($contentLength) { $this->_soapHeaders = array('POST /url HTTP/1.1', 'Host: '.SOAP_HOST, 'Content-Type: text/xml; charset=utf-8', 'Content-Length: '.$contentLength); } } class RoomParser extends SplObjectStorage { public function attach( Parseable $obj ) { parent::attach( $obj ); } public function parseRooms( $arr, $dept ) { for ( $this->rewind(); $this->valid(); $this->next() ) { $ret = $this->current()->parse( $arr, $dept ); echo $ret->getPrice(), PHP_EOL; } } } $arrive = '12/28/2010'; $depart = '01/02/2011'; $rooms = new RoomParser( $arrive, $depart); $rooms->attach( new Room( '12/28/2010', '01/02/2011') ); $rooms->attach( new Room( '12/29/2010', '01/04/2011') ); echo $rooms->count(), ' Rooms', PHP_EOL; Edit: I'm thinking it may be easier if I made the RoomParser less generic by storing properties that all the objects will share. Though I'll probably have to make methods if I want to override for a certain object.

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  • What is MVC and what are the advantages of it?

    - by Teifion
    I found What are mvp and mvc and what is the difference but it didn't really answer this question. I've recently started using MVC because it's part of the framework that myself and my work-partner are going to use. We chose it because it looked easy and separated process from display, are there advantages besides this that we don't know about and could be missing out on? Pros Display and Processing are seperated Cons None so far

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  • An existing connection was forcibly closed by the remote host

    - by Alexander
    I am about to give up debugging SMTP servers to send email... My code is the following private void SendMail() { SmtpClient mailClient = new SmtpClient("smtp.mail.yahoo.com", 465); mailClient.EnableSsl = true; MailMessage message = new MailMessage(); message.To.Add("[email protected]"); message.Subject = "i wish it would work"; MailAddress fromAddress = new MailAddress(Email.Text, Name.Text); message.From = fromAddress; mailClient.Send(message); }

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  • How can several different datatypes be saved in one table

    - by poseidon
    This is my situation: I am constructing an ad-like application in Django and Mysql. I am using a flexible-ad approach where we have: a table with ad categories (several categories such as home, furniture, cars, etc.) id_category name a table with details for the ad categories (home: area, squared meters. car: seats, color.) id_detail id_category (the categ the detail describes) name type (boolean, char, int, long, etc.) the ad table (i am selling a house. i am selling a car.) id_ad id_category text date a table where i plan to consolidate the details of the ads (home: A-area, 500 sq-meters. car: 5 seats, red.) id_detail_ad id_ad id_detail value Is this possible? Can I have a table of details for all the ads, even if details include numbers, texts, booleans, etc? Or would I have to save them all as text and then interpret them via code accordingly? Please express your opinions. Thank you.

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