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  • MySQL - Calculating fields on the fly vs storing calculated data

    - by Christian Varga
    Hi Everyone, I apologise if this has been asked before, but I can't seem to find an answer to a question that I have about calculating on the fly vs storing fields in a database. I read a few articles that suggested it was preferable to calculate when you can, but I would just like to know if that still applies to the following 2 examples. Example 1. Say you are storing data relating to a car. You store the fuel tank size in litres, and how many litres it uses per 100km. You also want to know how many KMs it can travel, which can be calculated from the tank size and economy. I see 2 ways of doing this: When a car is added or updated, calculate the amount of KMs and store this as a static field in the database. Every time a car is accessed, calculate the amount of KMs on the fly. Because the cars economy/tank size doesn't change (although it could be edited), the KMs is a pretty static value. I don't see why we would calculate it every single time the car is accessed. Wouldn't this waste cpu time as opposed to simply storing it in a separate field in the database and calculating only when a car is added or updated? My next example, which is almost an entirely different question (but on the same topic), relates to counting children. Let's say we have a app which has categories and items. We have a view where we display all the categories, and a count of all the items inside each category. Again, I'm wondering what's better. To perform a MySQL query to count all the items in each category every single time the page is accessed? Or store the count in a field in the categories table and update when an item is added / deleted? I know it is redundant to store anything that can be calculated, but I worry that calculating fields or counting records might be slow as opposed to storing the data in a field. If it's not then please let me know, I just want to learn about when to use either method. On a small scale I guess it wouldn't matter either way, but apps like Facebook, would they really count the amount of friends you have every time someone views your profile or would they just store it as a field? I'd appreciate any responses to both of these scenarios, and any resource that might explain the benefits of calculating vs storing. Thanks in advance, Christian

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  • Core Data fetch request with array

    - by JK
    I am trying to set a fetch request with a predicate to obtain records in the store whose identifiers attribute match an array of identifiers specified in the predicate e.g. NSString *predicateString = [NSString stringWithFormat:@"identifier IN %@", employeeIDsArray]; The employeeIDsArray contains a number of NSNumber objects that match IDs in the store. However, I get an error "Unable to parse the format string". This type of predicate works if it is used for filtering an array, but as mentioned, fails for a core data fetch. How should I set the predicate please?

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  • [Reloaded] Error while sorting filtered data from a GridView

    - by Bogdan M
    Hello guys, I have an error I cannot solve, on a ASP.NET website. One of its pages - Countries.aspx, has the following controls: a CheckBox called "CheckBoxNAME": < asp:CheckBox ID="CheckBoxNAME" runat="server" Text="Name" /> a TextBox called "TextBoxName": < asp:TextBox ID="TextBoxNAME" runat="server" Width="100%" Wrap="False"> < /asp:TextBox> a SQLDataSource called "SqlDataSourceCOUNTRIES", that selects all records from a Table with 3 columns - ID (Number, PK), NAME (Varchar2(1000)), and POPULATION (Number) called COUNTRIES < asp:SqlDataSource ID="SqlDataSourceCOUNTRIES" runat="server" ConnectionString="< %$ ConnectionStrings:myDB %> " ProviderName="< %$ ConnectionStrings:myDB.ProviderName %> " SelectCommand="SELECT COUNTRIES.ID, COUNTRIES.NAME, COUNTRIES.POPULATION FROM COUNTRIES ORDER BY COUNTRIES.NAME, COUNTRIES.ID"> < /asp:SqlDataSource> a GridView called GridViewCOUNTRIES: < asp:GridView ID="GridViewCOUNTRIES" runat="server" AllowPaging="True" AllowSorting="True" AutoGenerateColumns="False" DataSourceID="SqlDataSourceCOUNTRIES" DataKeyNames="ID" DataMember="DefaultView"> < Columns> < asp:CommandField ShowSelectButton="True" /> < asp:BoundField DataField="ID" HeaderText="Id" SortExpression="ID" /> < asp:BoundField DataField="NAME" HeaderText="Name" SortExpression="NAME" /> < asp:BoundField DataField="POPULATION" HeaderText="Population" SortExpression="POPULATION" /> < /Columns> < /asp:GridView> a Button called ButtonFilter: < asp:Button ID="ButtonFilter" runat="server" Text="Filter" onclick="ButtonFilter_Click"/> This is the onclick event: protected void ButtonFilter_Click(object sender, EventArgs e) { Response.Redirect("Countries.aspx?" + (this.CheckBoxNAME.Checked ? string.Format("NAME={0}", this.TextBoxNAME.Text) : string.Empty)); } Also, this is the main onload event of the page: protected void Page_Load(object sender, EventArgs e) { if (Page.IsPostBack == false) { if (Request.QueryString.Count != 0) { Dictionary parameters = new Dictionary(); string commandTextFormat = string.Empty; if (Request.QueryString["NAME"] != null) { if (commandTextFormat != string.Empty && commandTextFormat.EndsWith("AND") == false) { commandTextFormat += "AND"; } commandTextFormat += " (UPPER(COUNTRIES.NAME) LIKE '%' || :NAME || '%') "; parameters.Add("NAME", Request.QueryString["NAME"].ToString()); } this.SqlDataSourceCOUNTRIES.SelectCommand = string.Format("SELECT COUNTRIES.ID, COUNTRIES.NAME, COUNTRIES.POPULATION FROM COUNTRIES WHERE {0} ORDER BY COUNTRIES.NAME, COUNTRIES.ID", commandTextFormat); foreach (KeyValuePair parameter in parameters) { this.SqlDataSourceCOUNTRIES.SelectParameters.Add(parameter.Key, parameter.Value.ToUpper()); } } } } Basicly, the page displays in the GridViewCOUNTRIES all the records of table COUNTRIES. The scenario is the following: - the user checks the CheckBox; - the user types a value in the TextBox (let's say "ch"); - the user presses the Button; - the page loads displaying only the records that match the filter criteria (in this case, all the countries that have names containing "Ch"); - the user clicks on the header of the column called "Name" in order to sort the data in the GridView Then, I get the following error: ORA-01036: illegal variable name/number. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Data.OracleClient.OracleException: ORA-01036: illegal variable name/number Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Any help is greatly appreciated, tnks. PS: I'm using ASP.NET 3.5, under Visual Studio 2008, with an OracleXE database.

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  • Get data from html form to ruby in Ruby on Rails

    - by Maestro1024
    Get data from html form to ruby in Ruby on Rails I have some html like this <html> <h1>Text to PDF</h1> <textarea name="comments" cols="40" rows="5"> Enter your Text here... </textarea><br> <input type="submit" value="Submit" /> </form> </body> </html> I want to give the value of the text into the controller for this page/view. How do I do this with rails? I am new to rails, what is the mechanism for this? I don't need to write to the database just want to hand it to the controller. If there is a good tutorial for this sort of thing that would be great, I am not convince I am approaching this correctly.

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  • Displaying Data on the Form with C#

    - by The.Anti.9
    I'm searching files and returning lines that include the search text, and I'm not really sure the best way to display the information I get. Every time I get a match, I want to show, in some sort of control, the File it came from, and the whole text line. (aka streamreader.ReadLine() result). First I tried just putting it all in a read-only text box, but it doesn't have a scroll bar. What is the best form control to help me display this data neatly?

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  • NSContextManagedObject - Problem Accessing it

    - by Jacob
    I have tab bar navigation application and The problem is that in my root controller I am able to set its NSContextManagedObject to the app delegates...However when I try to do the same on the other controller the application freezes... This only happens in the ViewDidLoad but thats where I need to set it so I can fetch the data

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  • Read data from a Gif

    - by kojof
    hi, i have a requirement to read data from a gif. The gif is exported from a Bloomberg terminal and contains Stock Prices. Is there anyway of reading the Stock Prices off this gif? I'd prefer to do it in C#, but if there is any other programming language that is recommended, i would be grateful if you can share that with me. regards

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  • how to use trigger in Jquery to pass parameter data as well as control (this)

    - by Shantanu Gupta
    I am trying to use same validation funtion for all my controls. But I dont know much in jquery and not been able to pass event handler to the trigger. I want to pass textbox id to my custom function. How can i do this <script src="http://code.jquery.com/jquery-latest.js"></script> <script type="text/javascript"> $(document).ready(function(){ $("#txtFirstName").bind('focusout', function() { $(this).trigger("customblurfocus",[$(this).val(), $(this).val() + " Required !", "Ok !"]); } ); $(this).bind('customblurfocus',function(defaultInputValue,ErrorMessage,ValidMessage) {alert($(this).val()); if($(this).val()=="" || $(this).val()==defaultInputValue) { $(this).val(defaultInputValue); $(this).siblings("span[id*='error']").toggleClass("error_set").text(ErrorMessage).fadeOut(3000); } else { $(this).siblings("span[id*='error']").toggleClass("error_ok").text(ValidMessage).show(1000); } } ); }); </script>

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  • How to query data from a password protected https website

    - by Addie
    I'd like my application to query a csv file from a secure website. I have no experience with web programming so I'd appreciate detailed instructions. Currently I have the user login to the site, manually query the csv, and have my application load the file locally. I'd like to automate this by having the user enter his login information, authenticating him on the website, and querying the data. The application is written in C# .NET. The url of the site is: https://www2.emidas.com/default.asp. I've tested the following code already and am able to access the file once the user has already authenticated himself and created a manual query. System.Net.WebClient Client = new WebClient(); Stream strm = Client.OpenRead("https://www3.emidas.com/users/<username>/file.csv"); Here is the request sent to the site for authentication. I've angle bracketed the real userid and password. POST /pwdVal.asp HTTP/1.1 Accept: image/jpeg, application/x-ms-application, image/gif, application/xaml+xml, image/pjpeg, application/x-ms-xbap, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/x-shockwave-flash, */* User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.2; Tablet PC 2.0; OfficeLiveConnector.1.4; OfficeLivePatch.1.3; .NET4.0C; .NET4.0E) Content-Type: application/x-www-form-urlencoded Accept-Encoding: gzip, deflate Cookie: ASPSESSIONID<unsure if this data contained password info so removed>; ClientId=<username> Host: www3.emidas.com Content-Length: 36 Connection: Keep-Alive Cache-Control: no-cache Accept-Language: en-US client_id=<username>&password=<password>

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  • Reverse regular expressions to generate data

    - by Anton Gogolev
    In one of the StackOverflow Podcasts (the one where guys were discussing data generation for testing DBs -- either #11 or #12), Jeff mentioned something like "reverse regular expressions", which are used exactly for that purpose: given a regex, produce a string which will eventually match said regex. What is the correct term for this whole concept? Is this a well-known concept?

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  • Send POST data with FBML on Facebook

    - by rebellion
    I'm new at this, and I can't seem to find the documentation that explains this. But I want to create a Facebook page, where you can send POST data to an external server, preferably with AJAX. Can someone please point me in the right direction, as I'm stumbling blind.

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  • C++ priority queue structure used ?

    - by John Retallack
    While searching for some functions in C++ STL documentation I read that push and pop for priority queues needs constant time. "Constant (in the priority_queue). Although notice that push_heap operates in logarithmic time." My question is what kind of data structure is used to mantain a priority queue with O(1) for push and pop ?

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  • Data Structures for hashMap, List and Set

    - by harigm
    Can any one please guide me to look in depth about the Data Structures used and how is it implemented in the List, Set and Maps of Util Collection page. In Interviews most of the questions will be on the Algorithms, but I never saw anywhere the implementation details, Can any one please share the information.

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  • Error when pushing data to Heroku: time zone displacement out of range

    - by J. Pablo Fernández
    I run the following command to push the contents of my local database to Heroku: heroku db:push --app my-app and from my home computer it works flawlessly but from my work computer I get this error: Taps Server Error: PGError: ERROR: time zone displacement out of range: "2011-11-15 12:00:00.000000+5894114400" I'm not sure where that date is coming from, I can't find it in the data anywhere. Any ideas what's going on and/or how to fix it? Thanks.

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  • Why does this code generate an error? [closed]

    - by user559601
    <link rel="search" type="application/opensearchdescription+xml" href="http://b.static.ak.fbcdn.net/rsrc.php/yJ/r/H2SSvhJMJA-.xml" title="" /> <link rel="shortcut icon" href="http://static.ak.fbcdn.net/rsrc.php/y7/r/5875srnzL-I.ico" /></head> <body class="WelcomePage UIPage_LoggedOut mac Locale_en_US"> <div id="FB_HiddenContainer" style="position:absolute; top:-10000px; width:0px; height:0px;" ></div> <div id="blueBar" class="loggedOut"></div> <div id="globalContainer"><div id="dialogContainer"></div><div id="dropmenu_container"></div> <div id="content" class="fb_content clearfix"><div ><!-- 2365fa3194ecdc0cab15721ce967a9f8663937c7 --> <div class="WelcomePage_Container"><div class="loggedout_menubar_container"><div class="clearfix loggedout_menubar"><a class="lfloat" href="/" title="Go to Home"><img class="fb_logo img" src="http://static.ak.fbcdn.net/rsrc.php/yp/r/kk8dc2UJYJ4.png" alt="Facebook logo" width="170" height="36" /></a><div class="rfloat"><div class="menu_login_container"><form method="POST" action="https://login.facebook.com/login.php?login_attempt=1" id="login_form" onsubmit="return Event.__inlineSubmit(this,event)"><input type="hidden" name="charset_test" value="&euro;,&acute;,€,´,?,?,?" /><input type="hidden" name="lsd" value="hEICz" autocomplete="off" /><input type="hidden" id="locale" name="locale" value="en_US" autocomplete="off" /><table cellspacing="0"><tr><td class="html7magic"><label for="email">Email</label></td><td class="html7magic"><label for="pass">Password</label></td></tr><tr><td><input type="text" class="inputtext" name="email" id="email" tabindex="1" /></td><td><input type="password" class="inputtext" name="pass" id="pass" tabindex="2" /></td><td><label class="uiButton uiButtonConfirm"><input value="Login" tabindex="4" type="submit" /></label></td></tr><tr><td class="login_form_label_field"><input type="checkbox" class="inputcheckbox" value="1" id="persistent" name="persistent" checked="1" /><input type="hidden" name="default_persistent" value="1" /><label id="label_persistent" for="persistent">Keep me logged in</label></td><td class="login_form_label_field"><a href="http://www.facebook.com/reset.php" rel="nofollow">Forgot your password?</a></td></tr></table><input type="hidden" name="charset_test" value="&euro;,&acute;,€,´,?,?,?" /><input type="hidden" id="lsd" name="lsd" value="hEICz" autocomplete="off" /></form> </div></div></div></div><div class="WelcomePage_MainSell"><div class="WelcomePage_MainSellCenter clearfix"><div class="WelcomePage_MainSellLeft"><div class="WelcomePage_MainMessage">Facebook helps you connect and share with the people in your life.</div><div class="WelcomePage_MainMap">&nbsp;</div></div><div class="WelcomePage_MainSellRight"><div class="WelcomePage_SignUpSection"><div class="WelcomePage_SignUpMessage"><div class="WelcomePage_SignUpHeadline">Sign Up</div><div class="WelcomePage_SignUpSubheadline">It's free, and always will be.</div></div><div class="WelcomePage_SimpleReg" id="registration_container"><div><noscript><div id="no_js_box"><h2>Javascript is disabled on your browser.</h2><p>Please enable JavaScript on your browser or upgrade to a Javascript-capable browser to register for Facebook.</p></div></noscript><div id="simple_registration_container" class="simple_registration_container"><div id="reg_box"><form method="post" id="reg" name="reg" onsubmit="return function(event)&#123;return false;&#125;.call(this,event)!==false &amp;&amp; Event.__inlineSubmit(this,event)"><input type="hidden" autocomplete="off" name="post_form_id" value="c3a2bed7243b9a85f53d69f23a38da9d" /><input type="hidden" name="lsd" value="hEICz" autocomplete="off" /><input type="hidden" autocomplete="off" id="reg_instance" name="reg_instance" value="bpgeTawHFSiHa5-7SR4gbif7" /><input type="hidden" autocomplete="off" id="locale" name="locale" value="en_US" /><input type="hidden" autocomplete="off" id="terms" name="terms" value="on" /><input type="hidden" autocomplete="off" id="abtest_registration_group" name="abtest_registration_group" value="1" /><input type="hidden" autocomplete="off" id="referrer" name="referrer" value="" /><input type="hidden" autocomplete="off" id="md5pass" name="md5pass" value="" /><input type="hidden" autocomplete="off" id="validate_mx_records" name="validate_mx_records" value="1" /><input type="hidden" autocomplete="off" id="ab_test_data" name="ab_test_data" value="" /><div id="reg_form_box" class="large_form"><table class="uiGrid editor" cellspacing="0" cellpadding="1"><tbody><tr><td class="label">First Name:</td><td><div class="field_container"><input type="text" class="inputtext" id="firstname" name="firstname" /></div></td></tr><tr><td class="label">Last Name:</td><td><div class="field_container"><input type="text" class="inputtext" id="lastname" name="lastname" /></div></td></tr><tr><td class="label">Your Email:</td><td><div class="field_container"><input type="text" class="inputtext" id="reg_email__" name="reg_email__" /></div></td></tr><tr><td class="label">Re-enter Email:</td><td><div class="field_container"><input type="text" class="inputtext" id="reg_email_confirmation__" name="reg_email_confirmation__" /></div></td></tr><tr><td class="label">New Password:</td><td><div class="field_container"><input type="password" class="inputtext" id="reg_passwd__" name="reg_passwd__" value="" /></div></td></tr><tr><td class="label">I am:</td><td><div class="field_container"><div class="hidden_elem"><select><option></option><option></option></select><select><option></option><option></option></select></div><select class="select" name="sex" id="sex"><option value="0">Select Sex:</option><option value="1">Female</option><option value="2">Male</option></select></div></td></tr><tr><td class="label">Birthday:</td><td><div class="field_container"> <select class="" id="birthday_month" name="birthday_month" onchange="return run_with(this, [&quot;editor&quot;], function() &#123;editor_date_month_change(this, &quot;birthday_day&quot;, &quot;birthday_year&quot;);&#125;);"><option value="-1">Month:</option><option value="1">Jan</option>

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  • How To create Multicolumn TreeView with header and sorting in WPF?

    - by sachin
    Hi! i have created tree view demo in Visual Studio 2008 C# in WPF but i want to give header and when header is clicked it sort data. i want to create demo like this header1………….header2……….header3 -parent1…………..parent2………..parent3 …-child1……………-child1………….child1 ……child1……………-child1…………child1 -parent2…………..parent2………..parent2 …-child2……………-child2………….child2 ……child……………-child2…………child2 parent3…………….parent3………..parent3 plz suggest any link or samples code. thank you!

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  • Good ways to map a 2D side shooter (somewhat like liero, or soldat)

    - by Blaze
    I'm wondering what way would be best to render a 2D map for a shooter (these will be static maps) similar to Soldat. Multiple options I've considered are a tile based map (stored in txt files), or just creating different classes for the different terrains I plan to use and creating a data structure to read/store them in a file. (I want to also be able to include things like jumping/running on walls, sliding down walls/slopes ect) I feel like there must be a better way than either of these, but haven't been able to find definitive information :/ Thanks :)

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