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  • How to refactor these generic methods?

    - by Steve Crane
    I have written two nearly identical generic extension methods and am trying to figure out how I might refactor them into a single method. They differ only in that one operates on List and the other on List, and the properties I'm interested in are AssetID for AssetDocument and PersonID for PersonDocument. Although AssetDocument and PersonDocument have the same base class the properties are defined in each class so I don't think that helps. I have tried public static string ToCSVList<T>(this T list) where T : List<PersonDocument>, List<AssetDocument> thinking I might then be able to test the type and act accordingly but this results in the syntax error Type parameter 'T' inherits conflicting constraints These are the methods that I would like to refactor into a single method but perhaps I am simply going overboard and they would besat be left as they are. I'd like to hear what you think. public static string ToCSVList<T>(this T list) where T : List<AssetDocument> { var sb = new StringBuilder(list.Count * 36 + list.Count); string delimiter = String.Empty; foreach (var document in list) { sb.Append(delimiter + document.AssetID.ToString()); delimiter = ","; } return sb.ToString(); } public static string ToCSVList<T>(this T list) where T : List<PersonDocument> { var sb = new StringBuilder(list.Count * 36 + list.Count); string delimiter = String.Empty; foreach (var document in list) { sb.Append(delimiter + document.PersonID.ToString()); delimiter = ","; } return sb.ToString(); }

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  • Replacement for deprecated SQL Server User Defined Type with a bound Rule and Default

    - by Adam Jones
    We have a User Defined Data Type of YesNo which has an which is an alias for char(1). The type has a bound Rule (must be Y or N) and a Default (N). The aim of this is that when any of the development team create a new field of type YesNo the rule and default are automatically bound to the new column. Rules and Defaults have been deprecated and won't be available in the next a future version of SQL Server, is there another way to achieve the same functionality? I should add that I'm aware that I could use CHECK and DEFAULT constraints to replicate the functionality of the bound Rule and Defalut objects, however these would have to be applied at each usage of the type, rather than getting the functionality 'for free' by using a UDT which has a bound Rule and Default. The post relates to a database that backs an existing application, rather than a new development, so I'm aware that our use of UDT's is less than optimal. I suspect the answer to the question is 'No', however normally when features are deprecated there's usually an alternative syntax that can be used as a drop in replacement so I wanted to pose the question in-case someone knew of an alternative.

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  • Using a class within a class?

    - by Josh
    I built myself a MySQL class which I use in all my projects. I'm about to start a project that is heavily based on user accounts and I plan on building my own class for this aswell. The thing is, a lot of the methods in the user class will be MySQL queries and methods from the MySQL class. For example, I have a method in my user class to update someone's password: class user() { function updatePassword($usrName, $newPass) { $con = mysql_connect('db_host', 'db_user', 'db_pass'); $sql = "UPDATE users SET password = '$newPass' WHERE username = '$userName'"; $res = mysql_query($sql, $con); if($res) return true; mysql_close($con); } } (I kind of rushed this so excuse any syntax errors :) ) As you can see that would use MySQL to update a users password, but without using my MySQL class, is this correct? I see no way in which I can use my MySQL class within my users class without it seeming dirty. Do I just use it the normal way like $DB = new DB();? That would mean including my mysql.class.php somewhere too... I'm quite confused about this, so any help would be appreciated, thanks.

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  • Subquery max sequence number

    - by Andy Levesque
    I'm hesitant to ask because I'm sure it's out there, but I just can't seem to come up with the keywords to find the answer. I'm stepping outside my boundaries by starting with subqueries (normally an Access user). I have a query that has TECH_ID, SEQ_NBR, and PELL_FT_AWD_AMT SELECT ISRS_V_NEED_ANAL_RESULT_PARENT.TECH_ID, ISRS_V_NEED_ANAL_RESULT_PARENT.AWD_YR, ISRS_V_NEED_ANAL_RESULT_PARENT.PELL_FT_AWD_AMT, ISRS_V_NEED_ANAL_RESULT_PARENT.SEQ_NBR FROM ISRS_V_NEED_ANAL_RESULT_PARENT GROUP BY ISRS_V_NEED_ANAL_RESULT_PARENT.TECH_ID, ISRS_V_NEED_ANAL_RESULT_PARENT.AWD_YR, ISRS_V_NEED_ANAL_RESULT_PARENT.PELL_FT_AWD_AMT, ISRS_V_NEED_ANAL_RESULT_PARENT.SEQ_NBR HAVING (((ISRS_V_NEED_ANAL_RESULT_PARENT.AWD_YR)="2013")) ORDER BY ISRS_V_NEED_ANAL_RESULT_PARENT.TECH_ID; What I want to return is add a subquery that selects only the max SEQ_NUM for each record, but I can't seem to get the syntax right. In the past I would cheat and have a separate query that first gave me the TECH_ID and max SEQ_NUM, and then have a second query that use the original table and the first query in a join to get the rest. How can I do this in one query? Example: TECH_ID SEQ_NUM PELL 1 1 4000 1 2 4000 1 3 5000 Using just the max of the sequence number still returns: 1; 2; 4000 and 1; 3; 5000 when I'm only wanting the latter.

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  • Trying to modify the text of a document onkeydown is inserting text incorrectly.

    - by Benny
    I have the following html: <html> <head> <script> function myKeyDown() { var myDiv = document.getElementById('myDiv'); myDiv.innerHTML = myDiv.innerHTML.replace(/(@[a-z0-9_]+)/gi, '<strong>$1</strong>'); } function init() { document.addEventListener('keydown', myKeyDown, false); document.designMode = "on"; } window.onload = init; </script> </head> <body> <div id="myDiv"> This is my variable name: @varname. If I type here things go wrong... </div> </body> </html> My goal is to do a kind of syntax highlighting on edit, to highlight variable names that begin with an @ symbol. However, when I edit the document's body, the function runs but the cursor is automatically shifted to the beginning of the body before the keystroke is performed. My hypothesis is that the keypress event is trying to insert the new character at a specified index, but when I run the replace function the indices get messed up so it defaults the character insertion point to the beginning. I'm using Firefox to test by the way. Any help would be appreciated. Thanks, B.J.

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  • Using Rails Helper Methods within ActionRecord Queries?

    - by Pygmalion
    I have a table of events (in a sqlite3 database for what it's worth) with a column called "when" that contains a timestamp detailing precisely when the event that particular row denotes is set to occur. Right now, I have @events = Event.find(:all) in my controller and I am using template helper methods to calculate where to place each event on my display page based on the day of the week it occurs on. For example: <% if(event.when.wday == 6) %> # DO SOMETHING <% end %> I want to abstract this logic to the controller however. My idea was to do the following: @thursday_events = Event.find(:all, :conditions => ["when.wday=4"]) Obviously (I guess?) this didn't work. Throwing the error "SQLite3::SQLException: near "when": syntax error: SELECT * FROM "events" WHERE (when.wday=4)". I'm assuming this is because I tried to use a helper method within a find condition but I don't know a better way to do this. Any advice? Thanks!

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  • Why can't I pass an argument to create this window using wxpython?

    - by somefreakingguy
    I am trying to learn how to make a GUI in python! Following an online tutorial, I found that the following code 'works' in creating an empty window: import wx from sys import argv class bucky(wx.Frame): def __init__(self, parent, id): wx.Frame.__init__(self, parent, id, 'Frame aka window', size=(300, 200)) if __name__=='__main__': app=wx.PySimpleApp() frame=bucky(parent=None,id=-1) frame.Show() app.MainLoop() That gives me a window, which is great. However, what if I want to get an argument passed onto the program to determine the window size? I thought something like this ought to do the trick: import wx from sys import argv script, x, y = argv class mywindow(wx.Frame): def __init__(self, parent, id): wx.Frame.__init__(self, parent, id, 'Frame aka window', size=(x, y)) if __name__=='__main__': app=wx.PySimpleApp() frame=mywindow(parent=None,id=-1) frame.Show() app.MainLoop() But, alas, that does not work! Nor does the raw_input() function pass on the value. I keep getting the following error: C:/Python26/pythonw.exe -u "C:/Documents and Settings/Owner/Desktop/wz.py" File "C:/Documents and Settings/Owner/Desktop/wz.py", line 8 wx.Frame.__init__(self, parent, id, 'Frame aka window', size=(x y)) ^ SyntaxError: invalid syntax Thanks for the help!

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  • Handling XMLHttpRequest to call external application

    - by Ian
    I need a simple way to use XMLHttpRequest as a way for a web client to access applications in an embedded device. I'm getting confused trying to figure out how to make something thin and light that handles the XMLHttpRequests coming to the web server and can translate those to application calls. The situation: The web client using Ajax (ExtJS specifically) needs to send and receive asynchronously to an existing embedded application. This isn't just to have a thick client/thin server, the client needs to run background checking on the application status. The application can expose a socket interface, with a known set of commands, events, and configuration values. Configuration could probably be transmitted as XML since it comes from a SQLite database. In between the client and app is a lighttpd web server running something that somehow handles the translation. This something is the problem. What I think I want: Lighttpd can use FastCGI to route all XMLHttpRequest to an external process. This process will understand HTML/XML, and translate between that and the application's language. It will have custom logic to simulate pushing notifications to the client (receive XMLHttpRequest, don't respond until the next notification is available). C/C++. I'd really like to avoid installing Java/PHP/Perl on an embedded device. So I'll need more low level understanding. How do I do this? Are there good C++ libraries for interpreting the CGI headers and HTML so that I don't have to do any syntax processing, I can just deal with the request/response contents? Are there any good references to exactly what goes on, server side, when handling the XMLHttpRequest and CGI interfaces? Is there any package that does most of this job already, or will I have to build the non-HTTP/CGI stuff from scratch? Thanks for any help! I am really having trouble learning about the server side of these technologies.

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  • How to non-greedy multiple lookbehind matches

    - by ArtK
    Source: <prefix><content1><suffix1><prefix><content2><suffix2> Engine: PCRE RegEx1: (?<=<prefix>)(.*)(?=<suffix1>) RegEx2: (?<=<prefix>)(.*)(?=<suffix2>) Result1: <content1> Result2: <content1><suffix1><prefix><content2> The desired result for RegEx2 is just <content2> but it is obviously greedy. How do I make RegEx2 non-greedy and use only the last matching lookbehind? [I hope I have translated this correctly from the NoteTab syntax. I don't do much RegEx coding. The <prefix>, <content> & <suffix> terms are just meant to represent arbitrary strings. Only the "<" in the "?<=" lookbehind command is significant.] I suspect it is something simple but after too many hours of searching I'm giving up on solving it myself. Thanks for the help Art

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  • Destructuring assignment in JavaScript

    - by Anders Rune Jensen
    As can be seen in the Mozilla changlog for JavaScript 1.7 they have added destructuring assignment. Sadly I'm not very fond of the syntax (why write a and b twice?): var a, b; [a, b] = f(); Something like this would have been a lot better: var [a, b] = f(); That would still be backwards compatible. Python-like destructuring would not be backwards compatible. Anyway the best solution for JavaScript 1.5 that I have been able to come up with is: function assign(array, map) { var o = Object(); var i = 0; $.each(map, function(e, _) { o[e] = array[i++]; }); return o; } Which works like: var array = [1,2]; var _ = assign[array, { var1: null, var2: null }); _.var1; // prints 1 _.var2; // prints 2 But this really sucks because _ has no meaning. It's just an empty shell to store the names. But sadly it's needed because JavaScript doesn't have pointers. On the plus side you can assign default values in the case the values are not matched. Also note that this solution doesn't try to slice the array. So you can't do something like {first: 0, rest: 0}. But that could easily be done, if one wanted that behavior. What is a better solution?

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  • SQL Server Reset Identity Increment for all tables

    - by DanSpd
    Basically I need to reset Identity Increment for all tables to its original. Here I tried some code, but it fails. http://pastebin.com/KSyvtK5b actual code from link: USE World00_Character GO -- Create a cursor to loop through the System Ojects and get each table name DECLARE TBL_CURSOR CURSOR -- Declare the SQL Statement to cursor through FOR ( SELECT Name FROM Sysobjects WHERE Type='U' ) -- Declare the @SQL Variable which will hold our dynamic sql DECLARE @SQL NVARCHAR(MAX); SET @SQL = ''; -- Declare the @TblName Variable which will hold the name of the current table DECLARE @TblName NVARCHAR(MAX); -- Open the Cursor OPEN TBL_CURSOR -- Setup the Fetch While that will loop through our cursor and set @TblName FETCH NEXT FROM TBL_CURSOR INTO @TblName -- Do this while we are not at the end of the record set WHILE (@@FETCH_STATUS <> -1) BEGIN -- Appeand this table's select count statement to our sql variable SET @SQL = @SQL + ' ( SELECT '''+@TblName+''' AS Table_Name,COUNT(*) AS Count FROM '+@TblName+' ) UNION'; -- Delete info EXEC('DBCC CHECKIDENT ('+@TblName+',RESEED,(SELECT IDENT_SEED('+@TblName+')))'); -- Pull the next record FETCH NEXT FROM TBL_CURSOR INTO @TblName -- End the Cursor Loop END -- Close and Clean Up the Cursor CLOSE TBL_CURSOR DEALLOCATE TBL_CURSOR -- Since we were adding the UNION at the end of each part, the last query will have -- an extra UNION. Lets trim it off. SET @SQL = LEFT(@SQL,LEN(@SQL)-6); -- Lets do an Order By. You can pick between Count and Table Name by picking which -- line to execute below. SET @SQL = @SQL + ' ORDER BY Count'; --SET @SQL = @SQL + ' ORDER BY Table_Name'; -- Now that our Dynamic SQL statement is ready, lets execute it. EXEC (@SQL); GO error message: Error: Msg 102, Level 15, State 1, Line 1 Incorrect syntax near '('. How can I either fix that SQL or reset identity for all tables to its original? Thank you

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  • Databinding to Classmember of Classmember

    - by Walter
    Hello, I need some help about WPF and Databinding. Let's say I have a ClassA with a member of ClassB. ClassB has again a member, maybe an int: ClassB { public int MemberOfB { get; set; } } ClassA { private ClassB _theB; public ClassB MemberOfA { get {return _theB;} set { _theB = value; // Need to do something here... } } } When I have a Databinding in XAML like this: <TextBox Text="{Binding Path=MemberOfA.MemberOfB}"/> Where the Datacontext of the Textbox is an object of type ClassA. As you can see, i need to do some computations in the setter of MemberOfA in ClassA. But with the databinding above, this setter is of course never called, because it binds to the member of ClassB. So, how can i get to be informed if the MemberOfA changes (when I Type something into the Textbox)? Are there any best practices? (Didn't check the code in Visual Studio, so there may be some syntax errors). Thanks, Walter

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  • wordpress categories and their subcategories

    - by Ayrton
    Hi I'm looking to obtain all the (parent) categories with their children accordingly (assuming you don't have grandchildren) and make the following structure <div class="box"> <h3><a href="#">Parent Category I</a></h3> <ul> <li><a href="#">sub cat 1</a></li> <li><a href="#">sub cat 2</a></li> <li><a href="#">sub cat 3</a></li> </ul> </div> <div class="box"> <h3><a href="#">Parent Category II</a></h3> <ul> <li><a href="#">sub cat 1</a></li> <li><a href="#">sub cat 2<</a></li> <li><a href="#">sub cat 3</a></li> </ul> </div> I figured it's something like (don't mind the syntax) however I don't know how to obtain those (parent)categories and their children: $parents = ... ; foreach($parents as $parent){ <div> <h3>$parent</h3> $children = ...; <ul> foreach ($children as $child){ <li>$child</li> } </ul> </div> }

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  • how do i execute a stored procedure with vici coolstorage?

    - by lincolnk
    I'm building an app around Vici Coolstorage (asp.net version). I have my classes created and mapped to my database tables and can pull a list of all records fine. I've written a stored procedure where the query jumps across databases that aren't mapped with Coolstorage, however, the fields in the query result map directly to one of my classes. The procedure takes 1 parameter. so 2 questions here: how do i execute the stored procedure? i'm doing this CSParameterCollection collection = new CSParameterCollection(); collection.Add("@id", id); var result = Vici.CoolStorage.CSDatabase.RunQuery("procedurename", collection); and getting the exception "Incorrect syntax near 'procedurename'." (i'm guessing this is because it's trying to execute it as text rather than a procedure?) and also, since the class representing my table is defined as abstract, how do i specify that result should create a list of MyTable objects instead of generic or dynamic or whatever objects? if i try Vici.CoolStorage.CSDatabase.RunQuery<MyTable>(...) the compiler yells at me for it being an abstract class.

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  • How do I reset a form in an ajax callback?

    - by B.Gordon
    I am sending a form using simple ajax and returning the results in a div above the form. The problem is that after the form is submitted and validated, I display a thank you and want to reset the form so they don't just press the submit button again... Can't seem to find the right code to do this... <form id="myForm" target="sendemail.php" method="post"> <div id="results"></div> <input type="text" name="value1"> <input type="text" name="value2"> <input type="submit" name="submit"> </form> So, my sendemail.php validation errors and success messages appear in #results without problems. But... when I try to send back a javascript form reset command, it does not work. Naturally I cannot see it in the source code since it is an AJAX callback so I don't know if that is the issue or if I am just using the wrong syntax. echo "<p>Thank you. Your message has been accepted for delivery.</p>"; echo "<script type=\"text/javascript\">setTimeout('document.getElementById('myForm').reset();',1000);</script>"; Any ideas gurus?

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  • Best way to organize filetype settings in .vim and .vimrc?

    - by dimatura
    I'm going through my vim dotfiles to tidy them up. I've noticed that through time I've added various filetype specific settings in various inconsistent ways. Let's suppose I'm customizing for Python: au BufRead,BufNewfFile *.py (do something). I don't like this because some Python files might not have the .py termination. au FileType python (do something). This seems a better option because it doesn't depend on the file having the .py termination. The drawback is that Vim doesn't know about some filetypes. I can make Vim recognize additional filetypes, but I also have various inconsistent ways of doing it: a .vim/filetype.vim file, another in .vim/after/filetype.vim and various set filetype commands in .vimrc. Add a .vim/ftplugin/python.vim file with filetype specific settings. I understand the $VIMRUNTIME/ftplugin/python.vim can override whatever settings I make here. One problem is that I'm not sure how this interacts with .vim/filetype.vim and .vim/after/filetype.vim. Add a .vim/after/ftplugin/python.vim. I understand that this is loaded after $VIMRUNTIME/ftplugin/python.vim so it can overwrite settings from there. As in the previous method I'm not sure how it interacts with the filetype.vim files. So I have at least four ways of doing this, not mentioning syntax files and filetype-specific plugins. It seems to me the best way to do this is to put my filetype specific settings in after/ftplugin so they don't get overwritten, and filetypes.vim in after for the same reason. However, before I proceed I'd like to ask if anyone has suggestions about the best way to deal with filetype specific settings.

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  • Javascript for loop with variable

    - by Jascination
    I'm doing some simple javascript learning at the moment and I'm stuck on how to solve this problem. (the basic form comes from Code Academy). The task is to create 3 rabbit objects, each with a different adjective as an attribute. Then, print describeMyself() for each rabbit. Instead of repeating myself 3 times, I'd like to find a way to solve the problem with a for loop to make it more streamlined/challenging for myself. Here's what I tried: function Rabbit(adjective) { this.adjective = adjective; this.describeMyself = function() { console.log("I am a " + this.adjective + " rabbit"); }; } var rabbit1 = new Rabbit(fluffy); var rabbit2 = new Rabbit(happy); var rabbit3 = new Rabbit(sleepy); for (i=1; i<=3; i++){ ("rabbit"+i).describeMyself(); } Obviously, the ("rabbit"+i).describeMyself() is wrong. I want the loop to create "rabbit1", "rabbit2" and "rabbit3". What's the proper syntax here?

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  • C++ classes with members referencing each other

    - by Saad Imran.
    I'm trying to write 2 classes with members that reference each other. I'm not sure if I'm doing something wrong or it's just not possible. Can anyone help me out here... Source.cpp #include "Headers.h" using namespace std; void main() { Network* network = new Network(); system("pause"); return; } Headers.h #ifndef Headers_h #define Headers_h #include <iostream> #include <vector> #include "Network.h" #include "Router.h" #endif Network.h #include "Headers.h" class Network { protected: vector<Router> Routers; }; Router.h #include "Headers.h" class Router { protected: Network* network; public: }; The errors I'm getting are: error C2143: syntax error : missing ';' before '<' error C2238: unexpected token(s) preceding ';' error C4430: missing type specifier - int assumed. I'm pretty sure I'm not missing any semicolons or stuff like that. The program works find if I take out one of the members. I tried finding similar questions and the solution was to use pointers, but that's what I'm doing and it does't seem to be working!

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  • Moving a large number of files in one directory to multiple directories

    - by Axsuul
    I am looking to create a Windows batch script to move about 2,000 files and splitting them up so that there are 10 files per folder. I have attempted creating a batch script but the syntax really boggles my mind. Here is what I have so far @echo off :: Config parameters set /a groupsize = 10 :: initial counter, everytime counter is 1, we create new folder set /a n = 1 :: folder counter set /a nf = 1 for %%f in (*.txt) do ( :: if counter is 1, create new folder if %n% == 1 ( md folder%nf% set /a n += 1 ) :: move file into folder mv -Y %%f folder%nf%\%%f :: reset counter if larger than group size if %n% == %groupsize% ( set /a n = 1 ) else ( set /a n += 1 ) ) pause Basically what this script does is loop through each .txt file in the directory. It creates a new directory in the beginning and moves 10 files into that directory, then creates a new folder again and moves another 10 files into that directory, and so on. However, I'm having problems where the n variable is not being incremented in the loop? I'm sure there's other errors too since the CMD window closes on me even with pause. Any help or guidance is appreciated, thanks for your time!

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  • backbone js or knockout js as a web framework with jquery mobile

    - by Dan
    without trying to cause a mass discussion I would like some advice from the fellow users of stack overflow. I am about to start building a mobile website that gets it data from JSON that comes from a PHP rest api. I have looked into different mobile frameworks and feel that JQM will work best for us as we have the knowledge of jQuery even though a little large. Currently at work however we are using jQuery for all our sites and realise that now we are building a mobile website I need to think about javascript frameworks to move us onto a more MV* approach, which I understand the benefits of and will bring much needed structure to this mobile site and future web applications we may bring. I have made a comparision table where I have managed to bring the selection down to 2 - backbone and knockout. I have been looking around the web and it seems that there is more support for backbone in general and maybe even more support for backbone with JQM. http://jquerymobile.com/test/docs/pages/backbone-require.html One thing I have noticed however is that backbone doesnt support view bindings (declarative approach) whereas knockout does - is this a massive bonus? one of the main reasons for using a mv* for us is to get more structure - so I would like to use the library that will intergrate best with jQuery and especially jQuery mobile. neither of them seem to have that similar syntax... Thanks

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  • Row Source - combo box, filtering what pops up in a combo box by date

    - by primus285
    so I have a combo box that I want to pop up when somebody wants to search by year. It will allow them to see in that combo box only results that happened in a certain year. so far I have something like SELECT DISTINCT Database_New.ASEC FROM Database_New WHERE (((Database_New.Date) >= DateValue('01/01/2001') AND (((Database_New.Date) <= DateValue('12/031/2001'))); or SELECT DISTINCT Database_New.ASEC FROM Database_New WHERE (((Database_New.Date) >= BETWEEN DateValue('01/01/2001') AND DateValue('12/31/2001’))); as you can see, the kicker is that I am already sorting the thing with SELECT DISTINCT under the ASEC field. But I want to filter it one more by year so a whole bunch of ASEC values that didnt happen in that year (and there are quite a few that happen rarely, or would onyl be associeted with one year) do not pop up as avalible. so far I get an error like "Syntax error in query expression '(((Database_New.Date) = DateValue('01/01/2001') AND (((Database_New.Date) <= DateValue('12/031/2001')))' and I am a VBA person, not quite as good at debuggin SQL. Is it something easy? or will it simply not work the way I have it set up.

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  • Why can't I build this Javascript object?

    - by Alex Mcp
    I have an object I'm trying to populate from another object (that is, iterate over a return object to produce an object with only selected values from the original). My code looks like this: var collect = {}; function getHistoricalData(username){ $.getJSON("http://url/" + username + ".json?params", function(data){ for (var i=0; i < data.length; i++) { console.log(i); collect = { i : {text : data[i].text}}; $("#wrap").append("<span>" + data[i].text + "</span><br />"); }; console.log(collect); }); } So I'm using Firebug for debugging, and here's what I know: The JSON object is intact console.log(i); is showing the numbers 1-20 as expected When I log the collect object at the end, it's structure is this: var collect = { i : {text : "the last iteration's text"}}; So the incrementer is "applying" to the data[i].text and returning the text value, but it's not doing what I expected, which is create a new member of the collect object; it's just overwriting collect.i 20 times and leaving me with the last value. Is there a different syntax I need to be using for assigning object members? I tried collect.i.text = and collect[i].text = and the error was that whatever I tried was undefined. I'd love to know what's going on here, so the more in-depth an explanation the better. Thanks!

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  • Why put a DAO layer over a persistence layer (like JDO or Hibernate)

    - by Todd Owen
    Data Access Objects (DAOs) are a common design pattern, and recommended by Sun. But the earliest examples of Java DAOs interacted directly with relational databases -- they were, in essence, doing object-relational mapping (ORM). Nowadays, I see DAOs on top of mature ORM frameworks like JDO and Hibernate, and I wonder if that is really a good idea. I am developing a web service using JDO as the persistence layer, and am considering whether or not to introduce DAOs. I foresee a problem when dealing with a particular class which contains a map of other objects: public class Book { // Book description in various languages, indexed by ISO language codes private Map<String,BookDescription> descriptions; } JDO is clever enough to map this to a foreign key constraint between the "BOOKS" and "BOOKDESCRIPTIONS" tables. It transparently loads the BookDescription objects (using lazy loading, I believe), and persists them when the Book object is persisted. If I was to introduce a "data access layer" and write a class like BookDao, and encapsulate all the JDO code within this, then wouldn't this JDO's transparent loading of the child objects be circumventing the data access layer? For consistency, shouldn't all the BookDescription objects be loaded and persisted via some BookDescriptionDao object (or BookDao.loadDescription method)? Yet refactoring in that way would make manipulating the model needlessly complicated. So my question is, what's wrong with calling JDO (or Hibernate, or whatever ORM you fancy) directly in the business layer? Its syntax is already quite concise, and it is datastore-agnostic. What is the advantage, if any, of encapsulating it in Data Access Objects?

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  • sqlalchemy relation through another (declarative)

    - by clayg
    Is anyone familiar with ActiveRecord's "has_many :through" relations for models? I'm not really a Rails guy, but that's basically what I'm trying to do. As a contrived example consider Projects, Programmers, and Assignments: from sqlalchemy import create_engine from sqlalchemy.orm import sessionmaker from sqlalchemy import Column, ForeignKey from sqlalchemy.types import Integer, String, Text from sqlalchemy.orm import relation from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() class Assignment(Base): __tablename__ = 'assignment' id = Column(Integer, primary_key=True) description = Column(Text) programmer_id = Column(Integer, ForeignKey('programmer.id')) project_id = Column(Integer, ForeignKey('project.id')) def __init__(self, description=description): self.description = description def __repr__(self): return '<Assignment("%s")>' % self.description class Programmer(Base): __tablename__ = 'programmer' id = Column(Integer, primary_key=True) name = Column(String(64)) assignments = relation("Assignment", backref='programmer') def __init__(self, name=name): self.name = name def __repr__(self): return '<Programmer("%s")>' % self.name class Project(Base): __tablename__ = 'project' id = Column(Integer, primary_key=True) name = Column(String(64)) description = Column(Text) assignments = relation("Assignment", backref='project') def __init__(self, name=name, description=description): self.name = name self.description = description def __repr__(self): return '<Project("%s", "%s...")>' % (self.name, self.description[:10]) engine = create_engine('sqlite://') Base.metadata.create_all(engine) Session = sessionmaker(bind=engine) session = Session() Projects have many Assignments. Programmers have many Assignments. (understatement?) But in my office at least, Programmers also have many Projects - I'd like this relationship to be inferred through the Assignments assigned to the Programmer. I'd like the Programmer model to have a attribute "projects" which will return a list of Projects associated to the Programmer through the Assignment model. me = session.query(Programmer).filter_by(name='clay').one() projects = session.query(Project).\ join(Project.assignments).\ join(Assignment.programmer).\ filter(Programmer.id==me.id).all() How can I describe this relationship clearly and simply using the sqlalchemy declarative syntax? Thanks!

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  • Understanding F# Asynchronous Programming

    - by Yin Zhu
    I kind of know the syntax of asynchronous programming in F#. E.g. let downloadUrl(url:string) = async { let req = HttpWebRequest.Create(url) // Run operation asynchronously let! resp = req.AsyncGetResponse() let stream = resp.GetResponseStream() // Dispose 'StreamReader' when completed use reader = new StreamReader(stream) // Run asynchronously and then return the result return! reader.AsyncReadToEnd() } In F# expert book (and many other sources), they say like let! var = expr simply means "perform the asynchronous operation expr and bind the result to var when the operation completes. Then continue by executing the rest of the computation body" I also know that a new thread is created when performing async operation. My original understanding was that there are two parallel threads after the async operation, one doing I/O and one continuing to execute the async body at the same time. But in this example, I am confused at let! resp = req.AsyncGetResponse() let stream = resp.GetResponseStream() What happens if resp has not started yet and the thread in the async body wants to GetResponseStream? Is this a possible error? So maybe my original understanding was wrong. The quoted sentences in the F# expert book actually means that "creating a new thread, hang the current thread up, when the new thread finishes, wake up the body thread and continue", but in this case I don't see we could save any time. In the original understanding, the time is saved when there are several independent IO operations in one async block so that they could be done at the same time without intervention with each other. But here, if I don't get the response, I cannot create the stream; only I have stream, I can start reading the stream. Where's the time gained?

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