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  • SQL query - choosing 'last updated' record in a group, better db design?

    - by Jimmy
    Hi, Let's say I have a MySQL database with 3 tables: table 1: Persons, with 1 column ID (int) table 2: Newsletters, with 1 column ID (int) table 3: Subscriptions, with columns Person_ID (int), Newsletter_ID (int), Subscribed (bool), Updated (Datetime) Subscriptions.Person_ID points to a Person, and Subscription.Newsletter_ID points to a Newsletter. Thus, each person may have 0 or more subscriptions to 0 or more magazines at once. The table Subscriptions will also store the entire history of each person's subscriptions to each newsletter. If a particular Person_ID-Newsletter_ID pair doesn't have a row in the Subscriptions table, then it's equivalent to that pair having a subscription status of 'false'. Here is a sample dataset Persons ID 1 2 3 Newsletters ID 4 5 6 Subscriptions Person_ID Newsletter_ID Subscribed Updated 2 4 true 2010-05-01 3 4 true 2010-05-01 3 5 true 2010-05-10 3 4 false 2010-05-15 Thus, as of 2010-05-16, Person 1 has no subscription, Person 2 has a subscription to Newsletter 4, and Person 3 has a subscription to Newsletter 5. Person 3 had a subscription to Newsletter 4 for a while, but not anymore. I'm trying to do 2 kinds of query. A query that shows everyone's active subscriptions as of query time (we can assume that updated will never be in the future -- thus, this means returning the record with the latest 'updated' value for each Person_ID-Newsletter_ID pair, as long as Subscribed is true (if the latest record for a Person_ID-Newsletter_ID pair has a Subscribed status of false, then I don't want that record returned)). A query that returns all active subscriptions for a specific newsletter - same qualification as in 1. regarding records with 'false' in the Subscribed column. I don't use SQL/databases often enough to tell if this design is good, or if the SQL queries needed would be slow on a database with, say, 1M records in the Subscriptions table. I was using the Visual query builder tool in Visual Studio 2010 but I can't even get the query to return the latest updated record for each Person_ID-Newsletter_ID pair. Is it possible to come up with SQL queries that don't involve using subqueries (presumably because they would become too slow with a larger data set)? If not, would it be a better design to have a separate Subscriptions_History table, and every time a subscription status for a Person_ID-Newsletter-ID pair is added to Subscriptions, any existing record for that pair is moved to Subscriptions_History (that way the Subscriptions table only ever contains the latest status update for any Person_ID-Newsletter_ID pair)? I'm using .net on Windows, so would it be easier (or the same, or harder) to do this kind of queries using Linq? Entity Framework? Thanks!

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  • Please suggest me the best way to design my database.

    - by Raymond Ho
    I have a table named "Pages" and a table named "Categories". Each entry of the table "Pages" is linked to the table "Categories". The "Categories" table have 5 entries, they are: "Car", "Websites", "Technology", "Mobile Phones", and "Interest". So each time I put an entry to the "Pages" table, I need to map it to the "Categories" table so are arranged properly. Here's my table: Pages ______ id [PK] name url Categories ______ id [PK] Categoryname Pages2Categories ______ Pages.id Categories.id So my question is, is this the most efficient way to create this kind of relationships between tables? It seems very amateur

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  • What OpenGL functions are not GPU accelerated?

    - by Xavier Ho
    I was shocked when I read this (from the OpenGL wiki): glTranslate, glRotate, glScale Are these hardware accelerated? No, there are no known GPUs that execute this. The driver computes the matrix on the CPU and uploads it to the GPU. All the other matrix operations are done on the CPU as well : glPushMatrix, glPopMatrix, glLoadIdentity, glFrustum, glOrtho. This is the reason why these functions are considered deprecated in GL 3.0. You should have your own math library, build your own matrix, upload your matrix to the shader. For a very, very long time I thought most of the OpenGL functions use the GPU to do computation. I'm not sure if this is a common misconception, but after a while of thinking, this makes sense. Old OpenGL functions (2.x and older) are really not suitable for real-world applications, due to too many state switches. This makes me realise that, possibly, many OpenGL functions do not use the GPU at all. So, the question is: Which OpenGL function calls don't use the GPU? I believe knowing the answer to the above question would help me become a better programmer with OpenGL. Please do share some of your insights.

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  • Ruby proc vs lambda in initialize()

    - by Jimmy Chu
    I found out this morning that proc.new works in a class initialize method, but not lambda. Concretely, I mean: class TestClass attr_reader :proc, :lambda def initialize @proc = Proc.new {puts "Hello from Proc"} @lambda = lambda {puts "Hello from lambda"} end end c = TestClass.new c.proc.call c.lambda.call In the above case, the result will be: Hello from Proc test.rb:14:in `<main>': undefined method `call' for nil:NilClass (NoMethodError) Why is that? Thanks!

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  • Reading a line backwards

    - by Jimmy
    Hi, I'm using regular expression to count the total spaces in a line (first occurrence). match(/^\s*/)[0].length; However this reads it from the start to end, How can I read it from end to start. Thanks

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  • Which OpenGL functions are not GPU-accelerated?

    - by Xavier Ho
    I was shocked when I read this (from the OpenGL wiki): glTranslate, glRotate, glScale Are these hardware accelerated? No, there are no known GPUs that execute this. The driver computes the matrix on the CPU and uploads it to the GPU. All the other matrix operations are done on the CPU as well : glPushMatrix, glPopMatrix, glLoadIdentity, glFrustum, glOrtho. This is the reason why these functions are considered deprecated in GL 3.0. You should have your own math library, build your own matrix, upload your matrix to the shader. For a very, very long time I thought most of the OpenGL functions use the GPU to do computation. I'm not sure if this is a common misconception, but after a while of thinking, this makes sense. Old OpenGL functions (2.x and older) are really not suitable for real-world applications, due to too many state switches. This makes me realise that, possibly, many OpenGL functions do not use the GPU at all. So, the question is: Which OpenGL function calls don't use the GPU? I believe knowing the answer to the above question would help me become a better programmer with OpenGL. Please do share some of your insights.

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  • how to check some assembly is present in client and register that if not.

    - by Jimmy
    hi there, what i wana know is that how can i use assembly that is register in GAC in my C# application. Detail: What i wana achieved is that 1) Check ABC assembly that is register in my client machine or not from my windows application 2) If not then register that assemble in GAC of client from my windows application 3) And use this assembly and perform some functions Remember that that ABC assemble is my assembly having some of my function.

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  • MySQL + Joomla + remote c# access

    - by Jimmy
    Hello, I work on a Joomla web site, installed on a MySQL database and running on IIS7. It's all working fine. I now need to add functionality that lets (Joomla-)registered users change some configuration data. Though I haven't done this yet, it looks straightforward enough to do with Joomla. The data is private so all external access will be done through HTTPS. I also need an existing c# program, running on another machine, to read that configuration data. Sure enough, this data access needs to be as fast as possible. The data will be small (and filtered by query), but the latency should be kept to a minimum. A short-term, client-side cache (less than a minute, in case a user updates his configuration data) seems like a good idea. I have done practically zero database/asp programming so far, so what's the best way of doing that last step? Should the c# program access the database 'directly' (using what? LINQ?) or setup some sort of Facade (SOAP?) service? If a service should be used, should it be done through Joomla or with ASP on IIS? Thanks

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  • What is a great resource for learning about the implementation details of .NET generic collections?

    - by Jimmy W
    Hi all, I'm interested in understanding the underlying implementation details of generic collections in .NET. What I have in mind are details such as how the collections are stored, how each member of a collection is accessed by the CLR, etc. For collections that are analogous to traditional data structures, such as LinkedList and Dictionary, I think I have an understanding of what's going on underneath. However, I'm not as certain about collections like List (how is set up such that it is both indexable and expandable?) and SortedList, so any leads as to what I could look up to learn more about them would be greatly appreciated.

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  • Is 'donation' considered as commerical?

    - by Horace Ho
    I want to port an open source program to iPhone, the license prohibited any commercial use of the code. I emailed the author and he sent back an email saying freeware is ok. Of course I cannot (should not) charge anything on top of the code. Still, I want to get compensation for my work on UI design, graphics and integration work. So I wonder: Is donation (via PayPal) OK for my case? Is in-app purchase OK? i.e. the program is free, the user has the option to buy addition theme graphics? Thanks

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  • before filter not working as expected

    - by Jimmy
    Hey guys I have a ruby on rails app with a before filter setup in my application controller to ensure only the owner can edit a document, but my permission check is always failing even when it shouldn't. Here is the code: def get_logged_in_user id = session[:user_id] unless id.nil? @current_user = User.find(id) end end def require_login get_logged_in_user if @current_user.nil? session[:original_uri] = request.request_uri flash[:notice] = "You must login first." redirect_to login end end def check_current_user_permission require_login logger.debug "user id is #{params[:user_id]}" logger.debug "current user id is #{session[:user_id]}" if session[:user_id] != params[:user_id] flash[:notice] = "You don't have permission to do that." redirect_to :controller => 'home' end end The code to note is in the check_current_user_permission. Here is an example of my log output: user id is 3 current user id is 3 Redirected to http://localhost:3000/home Filter chain halted as [:check_current_user_permission] rendered_or_redirected. Can anyone shed some light into why this is failing? Obviously the user_id of 3 is equal to the session's user_id of 3. What is going wrong?

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  • Manage bad_alloc exception in C++ construtor

    - by Jimmy zhang
    I have Java experience and recently am doing some C++ coding. My question is that if I have class A, in which I have to instantiate class B and class C as two of the member variables of A. If in the constructor of A, should I assume that allocations of class B and C never fail, and handle the bad allocation exception in the destructor of A? If I don't make that assumption, meaning that I add some try catch block to catch bad_alloc of class B and class C, then if the allocation exception occurs, should I do clean up in the constructor of A? What are the recommended practices? If "new" generates a bad allocation, what value does the pointer carry?

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  • MySQL 5 in MySQL 4 compatible mode for one database?

    - by Horace Ho
    In a recent project, I have to maintain some PHP code. I set up a development server and installed MySQL, Apache, PHP, ..etc. The program is terminated with an error: Unknown column _ _ _ in 'on clause' Cannot select .... Google shows that it's a change of syntax around JOINs, parentheses are needed. As you may imagine, fixing all that PHP SQL strings will be the last resort. _< Is is possible to config MySQL 5 to run at MySQL 4 compatible mode? Or even better, for only one database? Thanks! p.s. Since we are going to host the code on a new production server (MySQL 5 on a CentOS box), the chance to install MySQL 4 on the new server might be slim.

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  • Get Data from Windows Form into C# program

    - by Jimmy
    I want my C# program to collect data. Then, when the OK button is clicked, I want this data to be loaded into my program -- such as into variables in Main(), or into data members of a class I have constructed, and I want the form to then go away -- not be hidden, but actually closed. Alas, read as I might in the book I have, the data collected by the form stays in the form, execution proceeds within the form, and the same form is used to display the result of the program's computations. Sheesh. All I want is to capture the form's information, close the form and proceed with my program. I would appreciate some tips on geting data from a form into Main() or into a class's data members. Thanks, Lucky

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