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  • How to program and calculate multiple subtotal and grandtotal using jquery?

    - by Victor
    I'm stump figuring out how to do this in jquery, I need to do it without any plug-in. Imagine a shopping cart for books, each change of quantity (using select dropdown) will update the total price, grandtotal and then the hidden input value. <table> <tr> <td class="qty"> <select class="item-1"> <option value="1">1</option> <option value="2">2</option> <option value="3">3</option> ... </select> </td> <td class="product"> Book 1 </td> <td class="price-item-1"> $20 </td> <td class="total-item-1"> $20 </td> </tr> <tr> <td class="qty"> <select class="item-2"> <option value="1">1</option> <option value="2">2</option> <option value="3">3</option> ... </select> </td> <td class="product"> Book 2 </td> <td class="price-item-2"> $10 </td> <td class="total-item-2"> $10 </td> </tr> ... ... <tr> <td colspan="3" align="right"> <strong>Grand Total:</strong> </td> <td class="grandtotal"> </td> </tr> </table> <input type="hidden" id="qty-item-1" value="0" /> <input type="hidden" id="total-item-1" value="0" /> <input type="hidden" id="qty-item-2" value="0" /> <input type="hidden" id="total-item-2" value="0" />

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  • In Ruby, how does coerce() actually work?

    - by Jian Lin
    It is said that when we have a class Point and knows how to perform point * 3 like the following: class Point def initialize(x,y) @x, @y = x, y end def *(c) Point.new(@x * c, @y * c) end end point = Point.new(1,2) p point p point * 3 Output: #<Point:0x336094 @x=1, @y=2> #<Point:0x335fa4 @x=3, @y=6> but then, 3 * point is not understood: Point can't be coerced into Fixnum (TypeError) So we need to further define an instance method coerce: class Point def coerce(something) [self, something] end end p 3 * point Output: #<Point:0x3c45a88 @x=3, @y=6> So it is said that 3 * point is the same as 3.*(point) that is, the instance method * takes an argument point and invoke on the object 3. Now, since this method * doesn't know how to multiply a point, so point.coerce(3) will be called, and get back an array: [point, 3] and then * is once again applied to it, is that true? point * 3 which is the same as point.*(3) and now, this is understood and we now have a new Point object, as performed by the instance method * of the Point class. The question is: 1) who invokes point.coerce(3) ? Is it Ruby automatically, or is it some code inside of * method of Fixnum by catching an exception? Or is it by case statement that when it doesn't know one of the known types, then call coerce? 2) Does coerce always need to return an array of 2 elements? Can it be no array? Or can it be an array of 3 elements? 3) And is the rule that, the original operator (or method) * will then be invoked on element 0, with the argument of element 1? (element 0 and element 1 are the two elements in that array returned by coerce) Who does it? Is it done by Ruby or is it done by code in Fixnum? If it is done by code in Fixnum, then it is a "convention" that everybody follows when doing a coerce? So could it be the code in * of Fixnum do something like this: if (something.typeof? ...) else if ... # other type else if ... # other type else # if it is not a type I know array = something.coerce(self) return array[0].*(array[1]) end

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  • Does Ruby on Rails "has_many" array provide data on a "need to know" basis?

    - by Jian Lin
    On Ruby on Rails, say, if the Actor model object is Tom Hanks, and the "has_many" fans is 20,000 Fan objects, then actor.fans gives an Array with 20,000 elements. Probably, the elements are not pre-populated with values? Otherwise, getting each Actor object from the DB can be extremely time consuming. So it is on a "need to know" basis? So does it pull data when I access actor.fans[500], and pull data when I access actor.fans[0]? If it jumps from each record to record, then it won't be able to optimize performance by doing sequential read, which can be faster on the hard disk because those records could be in the nearby sector / platter layer -- for example, if the program touches 2 random elements, then it will be faster just to read those 2 records, but what if it touches all elements in random order, then it may be faster just to read all records in a sequential way, and then process the random elements. But how will RoR know whether I am doing only a few random elements or all elements in random?

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  • Did anyone have this issue with a simple Facebook app or know how to solve it?

    - by Jian Lin
    I have a really simple few lines of Facebook app, using the new Facebook API: <pre> <?php require 'facebook.php'; // Create our Application instance. $facebook = new Facebook(array( 'appId' => '117676584930569', 'secret' => '**********', // hidden here on the post... 'cookie' => true, )); var_dump($facebook); ?> but it is giving me the following output: http://apps.facebook.com/woolaladev/i2.php would give out object(Facebook)#1 (6) { ["appId:protected"]=> string(15) "117676584930569" ["apiSecret:protected"]=> string(32) "**********" <--- just hidden on this post ["session:protected"]=> NULL ["sessionLoaded:protected"]=> bool(false) ["cookieSupport:protected"]=> bool(true) ["baseDomain:protected"]=> string(0) "" } Session is NULL for some reason, but I am logged in and can access my home and profile and run other apps on Facebook (to see that I am logged on). I am following the sample on: http://github.com/facebook/php-sdk/blob/master/examples/example.php http://github.com/facebook/php-sdk/blob/master/src/facebook.php (download using raw URL: wget http://github.com/facebook/php-sdk/raw/master/src/facebook.php ) Trying on both hosting companies at dreamhost.com and netfirms.com, and the results are the same.

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  • In CSS, how to not float a 300px wide Div to the next line?

    - by Jian Lin
    Say, there is a bar that is styled at the bottom of the viewport, using position: fixed; bottom: 0; left: 0; width: 100%; height 50px; overflow: hidden and then there are 4 Divs inside it, each one floated to the left. Each Div is about 300px wide or can be more (depending on the content) Now, when the window is 1200 pixel wide, and we see all 4 Divs, but when the window is resize to be 1180 pixel wide (just 20 pixels less), then the whole 300px wide Div will disappear, because it is "floated" to the next line. So how can this be made so that, the Div will stay there and showing 280px of itself, rather than totally disappear? By the way, white-space: nowrap won't work as that probably has to do with not wrapping inline content. I was thinking of putting another Div inside this Div, having a fixed width of 1200px or 2000px, so that all Divs will float on the same level in this inner Div, and the outer Div will cut it off with the overflow: hidden. But this seems more like a hack... since the wide of all those Divs can be dynamic, and setting a fixed width of 1200px or 2000px seems like too much of a hack.

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  • Strange behaviour with mediaplayer and seekTo

    - by Mathias Lin
    I'm implementing a custom video player because I need custom video controls. I have an app with only one activity, which on startup shall start playing a video right away. Now, the problem I have is: I don't want the video to start from the beginning, but from a later position. Therefore I do a seekTo(16867). Since seekTo is asynchronous, I place the start call of the mediaplayer (player.start()) in the onSeekComplete of the onSeekCompleteListener. The strange behaviour I experience though is that I can see/hear the video playing from the beginning for a few millisecs before it actually plays from/jumps to the position I seeked to. But - on the other hand - the Log output I call before the player.start returns the correct position 16867, where I seeked to. Below is the relevant code section, the complete class is at http://pastebin.com/jqAAFsuX (I'm on Nexus One / 2.2 StageFright) private void playVideo(String url) { try { btnVideoPause.setEnabled(false); if (player==null) { player=new MediaPlayer(); player.setScreenOnWhilePlaying(true); } else { player.stop(); player.reset(); } url = "/sdcard/myapp/main/videos/main.mp4"; // <--- just for test purposes hardcoded here now player.setDataSource(url); player.setDisplay(holder); player.setAudioStreamType(AudioManager.STREAM_MUSIC); player.setOnCompletionListener(this); player.setOnPreparedListener(this); player.setOnSeekCompleteListener(new MediaPlayer.OnSeekCompleteListener() { public void onSeekComplete(MediaPlayer mediaPlayer) { Log.d("APP", "current pos... "+ player.getCurrentPosition() ); player.start(); // <------------------ start video on seek completed player.setOnSeekCompleteListener(null); } }); player.prepareAsync(); } catch (Throwable t) { Log.e(TAG, "Exception in btnVideoPause prep", t); } } public void onPrepared(MediaPlayer mediaplayer) { width=player.getVideoWidth(); height=player.getVideoHeight(); if (width!=0 && height!=0) { holder.setFixedSize(width, height); progressBar.setProgress(0); progressBar.setMax(player.getDuration()); player.seekTo(16867); // <------------------ seeking to position } btnVideoPause.setEnabled(true); }

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  • How to skip all the column names in MySQL when the table has auto increment primary key?

    - by Jian Lin
    A table is: mysql> desc gifts; +---------------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------------+-------------+------+-----+---------+----------------+ | giftID | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(80) | YES | | NULL | | | filename | varchar(80) | YES | | NULL | | | effectiveTime | datetime | YES | | NULL | | +---------------+-------------+------+-----+---------+----------------+ the following is ok: mysql> insert into gifts -> values (10, "heart", "heart_shape.jpg", now()); Query OK, 1 row affected (0.05 sec) but is there a way to not specify the "10"... and just let each one be 11, 12, 13... ? I can do it using mysql> insert into gifts (name, filename, effectiveTime) -> values ("coffee", "coffee123.jpg", now()); Query OK, 1 row affected (0.00 sec) but the column names need to be all specified. Is there a way that they don't have to be specified and the auto increment of primary key still works? thanks.

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  • Thinking of an Inner Join as a Cross Join and then satisfying some condition(s)?

    - by Jian Lin
    It seems like the safest way to think of an Inner Join is to think of it as a Cross Join and then satisfying some condition(s)? Because the equi-join can be obvious, but the non-equi-join can be a bit confusing. But if we always use the Cross Join, and then filter out the ones satisfying the condition, then we get the resulting table. In other words, we can always analyze it by using the first record on the left table, and then go through every single records on the right, and then repeat that for 2nd record on the left, and for the 3rd, 4th, ... etc. So in our mind, we can analyze it using this way, and it is like O(n^2), although what happens in the DBMS maybe that it is a lot faster (when an index is present). Is there another good way to think of it besides this method?

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  • How can this closure test be written in other languages?

    - by Jian Lin
    I wonder how the following closure test can be written in other languages, such as C and Java. Can the same result be expected also in Perl, Python, and PHP? Ideally, we don't need to make a new local variable such as x and assign it the value of i inside the loop, but just so that i has a new copy in the new scope each time. (if possible). (some discussion is in this question.) The following is in Ruby, the "1.8.6" on the first line of result is the Ruby version which can be ignored. p RUBY_VERSION $foo = [] (1..5).each do |i| $foo[i] = lambda { p i } end (1..5).each do |j| $foo[j].call() end the print out is: [MacBook01:~] $ ruby scope.rb "1.8.6" 1 2 3 4 5 [MacBook01:~] $ Contrast that with another test, with i defined outside: p RUBY_VERSION $foo = [] i = 0 (1..5).each do |i| $foo[i] = lambda { p i } end (1..5).each do |j| $foo[j].call() end the print out: [MacBook01:~] $ ruby scope2.rb "1.8.6" 5 5 5 5 5 [MacBook01:~] $

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  • First programming language: PHP, Ruby, Python?

    - by Victor
    I've been a Web developer for over 5 years and am looking to start building more complex Web apps. Currently, I know HTML/CSS/Javascript but I feel it's time to start learning something else. I work with a lot of applications based on PHP. I created a vBulletin forum on my own time and I would definitely want to build off of that since it has gained a bit of popularity. I also work with Wordpress quite often. All of the software I work with tends to be based on PHP but I hear a lot of people say Ruby or Python is better. Since I'm starting out, I really don't care which one I learn but I want to start right. Any recommendations for someone with HTML/CSS/Javascript knowledge but wants to branch out?

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  • How can I modify my classes to use it's collections in WPF TreeView

    - by Victor
    Hello, i'am trying to modify my objects to make hierarchical collection model. I need help. My objects are Good and GoodCategory: public class Good { int _ID; int _GoodCategory; string _GoodtName; public int ID { get { return _ID; } } public int GoodCategory { get { return _GoodCategory; } set { _GoodCategory = value; } } public string GoodName { get { return _GoodName; } set { _GoodName = value; } } public Good(IDataRecord record) { _ID = (int)record["ID"]; _GoodtCategory = (int)record["GoodCategory"]; } } public class GoodCategory { int _ID; string _CategoryName; public int ID { get { return _ID; } } public string CategoryName { get { return _CategoryName; } set { _CategoryName = value; } } public GoodCategory(IDataRecord record) { _ID = (int)record["ID"]; _CategoryName = (string)record["CategoryName"]; } } And I have two Collections of these objects: public class GoodsList : ObservableCollection<Good> { public GoodsList() { string goodQuery = @"SELECT `ID`, `ProductCategory`, `ProductName`, `ProductFullName` FROM `products`;"; using (MySqlConnection conn = ConnectToDatabase.OpenDatabase()) { if (conn != null) { MySqlCommand cmd = conn.CreateCommand(); cmd.CommandText = productQuery; MySqlDataReader rdr = cmd.ExecuteReader(); while (rdr.Read()) { Add(new Good(rdr)); } } } } } public class GoodCategoryList : ObservableCollection<GoodCategory> { public GoodCategoryList () { string goodQuery = @"SELECT `ID`, `CategoryName` FROM `product_categoryes`;"; using (MySqlConnection conn = ConnectToDatabase.OpenDatabase()) { if (conn != null) { MySqlCommand cmd = conn.CreateCommand(); cmd.CommandText = productQuery; MySqlDataReader rdr = cmd.ExecuteReader(); while (rdr.Read()) { Add(new GoodCategory(rdr)); } } } } } So I have two collections which takes data from the database. But I want to use thats collections in the WPF TreeView with HierarchicalDataTemplate. I saw many post's with examples of Hierarlichal Objects, but I steel don't know how to make my objects hierarchicaly. Please help.

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  • Why is the ( ) mandatory in the SQL statement select * from gifts INNER JOIN sentgifts using (giftID

    - by Jian Lin
    Why is the ( ) mandatory in the SQL statement select * from gifts INNER JOIN sentgifts using (giftID); ? The ( ) usually is for specifying grouping of something. But in this case, are we supposed to be able to use 2 or more field names... in the example above, it can be all clear that it is 1 field, is it just that the parser is not made to bypass the ( ) when it is all clear? (such as in the language Ruby).

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  • In Ruby, why is a method invocation not be able to be treated as a unit when "do" and "end" is used?

    - by Jian Lin
    The following question is related to the question "Ruby Print Inject Do Syntax". My question is, can we insist on using do and end and make it work with puts or p? This works: a = [1,2,3,4] b = a.inject do |sum, x| sum + x end puts b # prints out 10 so, is it correct to say, inject is a class method of the Array class, which takes a block of code, and then returns a number. If so, then it should be no different from calling a function and getting back a return value: b = foo(3) puts b or b = circle.getRadius() puts b In the above two cases, we can directly say puts foo(3) puts circle.getRadius() so, there is no way to make it work directly by using the following 2 ways: a = [1,2,3,4] puts a.inject do |sum, x| sum + x end but it gives ch01q2.rb:7:in `inject': no block given (LocalJumpError) from ch01q2.rb:4:in `each' from ch01q2.rb:4:in `inject' from ch01q2.rb:4 grouping the method call using ( ) doesn't work either: a = [1,2,3,4] puts (a.inject do |sum, x| sum + x end) and this gives: ch01q3.rb:4: syntax error, unexpected kDO_BLOCK, expecting ')' puts (a.inject do |sum, x| ^ ch01q3.rb:4: syntax error, unexpected '|', expecting '=' puts (a.inject do |sum, x| ^ ch01q3.rb:6: syntax error, unexpected kEND, expecting $end end) ^ finally, the following version works: a = [1,2,3,4] puts a.inject { |sum, x| sum + x } but why doesn't the grouping of the method invocation using ( ) work in the earlier example? What if a programmer insist that he uses do and end, can it be made to work?

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  • It seems like the safest way to think of an Inner Join is to think of it as a Cross Join and then sa

    - by Jian Lin
    It seems like the safest way to think of an Inner Join is to think of it as a Cross Join and then satisfying some condition(s)? Because the equi-join can be obvious, but the non-equi-join can be a bit confusing. But if we always use the Cross Join, and then filter out the ones satisfying the condition, then we get the resulting table. In other words, we can always analyze it by using the first record on the left table, and then go through every single records on the right, and then repeat that for 2nd record on the left, and for the 3rd, 4th, ... etc. So in our mind, we can analyze it using this way, and it is like O(n^2), although what happens in the DBMS maybe that it is a lot faster (when an index is present). Is there another good way to think of it besides this method?

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  • file input - prevent selection of certain types of files and size

    - by Victor
    Is there a way to prevent the user from selecting a file that is not a specified file type when they browser for the file on their computer? For example, when a user browseses to upload an image file I would for them to only see images (jpg, png, ect.) that are less than 20mb. Is this something that can be accomplished with asp.net mvc and jquery or do I need to use flash or a java applet?

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  • Using jQuery's animate(), if the clicked on element is "<a href="#" ...> </a>", the fucntion should

    - by Jian Lin
    I was reading jQuery's page for animate() http://api.jquery.com/animate/ Its examples don't mention about if using <a href="#" id="clickme">click me</a> ... $('#clickme').click(function() { $('#someDiv').animate({left: "+=60"}); }) we actually still have to return false like in the old days? $('#clickme').click(function() { $('#someDiv').animate({left: "+=60"}); return false; }) (but then, those examples didn't use a <a> for the "click me"... but used something else. Otherwise the page will jump back to the beginning of the page? Does jQuery have a more elegant or magical way of doing it?

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  • Why in Ruby, a || 1 will throw an error when `a` is undefined, but a = a || 1 will not?

    - by Jian Lin
    When a is undefined, then a || 1 will throw an error, but a = a || 1 will not. Isn't that a little bit inconsistent? irb(main):001:0> a NameError: undefined local variable or method `a' for main:Object from (irb):1 from c:/ruby/bin/irb:12:in `<main>' irb(main):002:0> a || 1 NameError: undefined local variable or method `a' for main:Object from (irb):2 from c:/ruby/bin/irb:12:in `<main>' irb(main):003:0> a = a || 1 => 1

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  • Question about best practices and Macros from the book 'C++ Coding Standards'

    - by Victor T.
    From Herb Sutter and Andrei Alexandrescu's 'C++ Coding Standards', Item 16: Avoid Macros under Exceptions for this guideline they wrote: For conditional compilation (e.g., system-dependent parts), avoid littering your code with #ifdefs. Instead, prefer to organize code such that the use of macros drives alternative implementations of one common interface, and then use the interface throughout. I'm having trouble understanding exactly what they mean by this. How can you drive alternate implementations without the use of #ifdef conditional compile macro directives? Can someone provide an example to help illustrate what's being proposed by the above paragraph? Thanks

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  • C++ explicit template specialization of templated constructor of templated class

    - by Victor Liu
    I have a class like template <class T> struct A{ template <class U> A(U u); }; I would like to write an explicit specialization of this for a declaration like A<int>::A(float); In the following test code, if I comment out the specialization, it compiles with g++. Otherwise, it says I have the wrong number of template parameters: #include <iostream> template <class T> struct A{ template <class U> A(T t, U *u){ *u += U(t); } }; template <> template <> A<int>::A<int,float>(int t, float *u){ *u += U(2*t); } int main(){ float f = 0; int i = 1; A<int>(i, &f); std::cout << f << std::endl; return 0; }

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  • In SQL, we can use "Union" to merge two tables. What are different ways to do "Intersection"?

    - by Jian Lin
    In SQL, there is an operator to "Union" two tables. In an interview, I was told that, say one table has just 1 field with 1, 2, 7, 8 in it, and another table also has just 1 field with 2, and 7 in it, how do I get the intersection. I was stunned at first, because I never saw it that way. Later on, I found that it is actually a "Join" (inner join), which is just select * from t1, t2 where t1.number = t2.number (although the name "join" feels more like "union" rather than "intersect") another solution seems to be select * from t1 INTERSECT select * from t2 but it is not supported in MySQL. Are there different ways to get the intersection besides these two methods?

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  • Using Mercurial (hg), how to push just one file or one directory out?

    - by Jian Lin
    Using Mercurial, we can commit one file by using hg commit file.rb or 1 folder hg commit foldername But how can we push just 1 file or 1 folder out? The whole project can be pushed using hg push ssh://[email protected]//project/code/preliminary but there seems to be no way to push out just 1 file or 1 folder? I tried the following and they don't work: hg push ssh://[email protected]//project/code/preliminary app/views/index.html.erb or hg push ssh://[email protected]//project/code/preliminary/app/views/index.html.erb

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  • Recreation of DB using "mysql mydb < mydb.sql" is really slow when the table has tens of millions of

    - by Jian Lin
    It seems that a MySQL database that has a table with tens of millions of records will get a big INSERT INTO statement when the following mysqldump some_db > some_db.sql is done to back up the database. (is it 1 insert statement that handles all the records?) So when reconstructing the DB using mysql some_db < some_db.sql then the CPU is hardly busy (about 1.8% usage by the mysql process... I don't see a mysqld either?) and also the hard disk doesn't seem to be too busy... Last time, the whole restore process took 5 hours. Is there a way to make it faster? Such as, when doing mysqldump, can it break the INSERT statement into shorter ones, so that the mysql doesn't need to parse the line so hard when restoring the DB?

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  • In SQL, can we always write an inner join statement as a main query and subquery if we only want to

    - by Jian Lin
    In SQL, can we always write an inner join statement as a main query and subquery or vice versa if we only want to find the intersection? For example, select * from gifts g where g.giftID in (select giftID from sentGifts); can do a join and show the gifts sent in the sentGifts table, but it won't be able to show the sentTime because that is inside the subquery. But if all we care is to find the intersection, without caring what is being displayed, then we can always convert one to the other?

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