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  • Declarative JDOQL vs Single-String JDOQL : performance

    - by DrDro
    When querying with JDOQL is there a performance difference between using the declarative version and the Single-String version: Example from the JDOQL doc: //Declarative JDOQL : Query q = pm.newQuery(org.jpox.Person.class, "lastName == \"Jones\" && age < age_limit"); q.declareParameters("double age_limit"); List results = (List)q.execute(20.0); //Single-String JDOQL : Query q = pm.newQuery("SELECT FROM org.jpox.Person WHERE lastName == \"Jones\"" + " && age < :age_limit PARAMETERS double age_limit"); List results = (List)q.execute(20.0); Other then performance, are there any reasons for which one is better to use then the other or is it just about the one with which we feel more comfortable.

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  • When to use identity comparison instead of equals?

    - by maaartinus
    I wonder why would anybody want to use identity comparison for fields in equals, like here (Java syntax): class C { private A a; public boolean equals(Object other) { // standard boring prelude if (other==this) return true; if (other==null) return false; if (other.getClass() != this.getClass()) return false; C c = (C) other; // the relevant part if (c.a != this.a) return false; // more tests... and then return true; } // getter, setters, hashCode, ... } Using == is a bit faster than equals and a bit shorter (due to no need for null tests), too, but in what cases (if any) you'd say it's really better to use == for fields inside equals?

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  • What is use of universal character names in identifiers in C++

    - by Jan Hudec
    The C++ standard (I noticed it in the new one, but it did already exist in C++03) specifies universal character names, written as \uNNNN and \UNNNNNNNN and representing the characters with unicode codepoints NNNN/NNNNNNNN. This is useful with string literals, especially since explicitly UTF-8, UTF-16 and UCS-4 string literals are also defined. However, the universal character literals are also allowed in identifiers. What is the motivation behind that? The syntax is obviously totally unreadable, the identifiers may be mangled for the linker and it's not like there was any standard function to retrieve symbols by name anyway. So why would anybody actually use an identifier with universal character literals in it? Edit: Since it actually existed in C++03 already, additional question would be whether you actually saw a code that used it?

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  • Using Delegates in C# (Part 1)

    - by rajbk
    This post provides a very basic introduction of delegates in C#. Part 2 of this post can be read here. A delegate is a class that is derived from System.Delegate.  It contains a list of one or more methods called an invocation list. When a delegate instance is “invoked” with the arguments as defined in the signature of the delegate, each of the methods in the invocation list gets invoked with the arguments. The code below shows example with static and instance methods respectively: Static Methods 1: using System; 2: using System.Linq; 3: using System.Collections.Generic; 4: 5: public delegate void SayName(string name); 6: 7: public class Program 8: { 9: [STAThread] 10: static void Main(string[] args) 11: { 12: SayName englishDelegate = new SayName(SayNameInEnglish); 13: SayName frenchDelegate = new SayName(SayNameInFrench); 14: SayName combinedDelegate =(SayName)Delegate.Combine(englishDelegate, frenchDelegate); 15: 16: combinedDelegate.Invoke("Tom"); 17: Console.ReadLine(); 18: } 19: 20: static void SayNameInFrench(string name) { 21: Console.WriteLine("J'ai m'appelle " + name); 22: } 23: 24: static void SayNameInEnglish(string name) { 25: Console.WriteLine("My name is " + name); 26: } 27: } We have declared a delegate of type SayName with return type of void and taking an input parameter of name of type string. On line 12, we create a new instance of this delegate which refers to a static method - SayNameInEnglish.  SayNameInEnglish has the same return type and parameter list as the delegate declaration.  Once a delegate is instantiated, the instance will always refer to the same target. Delegates are immutable. On line 13, we create a new instance of the delegate but point to a different static method. As you may recall, a delegate instance encapsulates an invocation list. You create an invocation list by combining delegates using the Delegate.Combine method (there is an easier syntax as you will see later). When two non null delegate instances are combined, their invocation lists get combined to form a new invocation list. This is done in line 14.  On line 16, we invoke the delegate with the Invoke method and pass in the required string parameter. Since the delegate has an invocation list with two entries, each of the method in the invocation list is invoked. If an unhandled exception occurs during the invocation of one of these methods, the exception gets bubbled up to the line where the invocation was made (line 16). If a delegate is null and you try to invoke it, you will get a System.NullReferenceException. We see the following output when the method is run: My name is TomJ'ai m'apelle Tom Instance Methods The code below outputs the same results as before. The only difference here is we are creating delegates that point to a target object (an instance of Translator) and instance methods which have the same signature as the delegate type. The target object can never be null. We also use the short cut syntax += to combine the delegates instead of Delegate.Combine. 1: public delegate void SayName(string name); 2: 3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: Translator translator = new Translator(); 9: SayName combinedDelegate = new SayName(translator.SayNameInEnglish); 10: combinedDelegate += new SayName(translator.SayNameInFrench); 11:  12: combinedDelegate.Invoke("Tom"); 13: Console.ReadLine(); 14: } 15: } 16: 17: public class Translator { 18: public void SayNameInFrench(string name) { 19: Console.WriteLine("J'ai m'appelle " + name); 20: } 21: 22: public void SayNameInEnglish(string name) { 23: Console.WriteLine("My name is " + name); 24: } 25: } A delegate can be removed from a combination of delegates by using the –= operator. Removing a delegate from an empty list or removing a delegate that does not exist in a non empty list will not result in an exception. Delegates are invoked synchronously using the Invoke method. We can also invoke them asynchronously using the BeginInvoke and EndInvoke methods which are compiler generated.

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  • iPhone OSStatus -25308 or errSecInteractionNotAllowed SFHFKeychainUtils

    - by George Octavio
    Hi again guys. I'm trying to access my iPhone's device keychain. I want to access in order to create a simple user-password value intended for a log in function. This is the code I'm using from SFHFKeychainUtils NSArray *keys = [[[NSArray alloc] initWithObjects: (NSString *) kSecClass, kSecAttrService, kSecAttrLabel, kSecAttrAccount, kSecValueData, nil] autorelease]; NSArray *objects = [[[NSArray alloc] initWithObjects: (NSString *) kSecClassGenericPassword, serviceName, serviceName, @"TestUser", @"TestPass", nil] autorelease]; NSDictionary *query = [[[NSDictionary alloc] initWithObjects: objects forKeys: keys] autorelease]; OSStatus status = SecItemAdd((CFDictionaryRef) query, NULL); } else if (status != noErr) { //Output to screen with error code goes here return NO; } return YES; } The error code I'm getting is OSStatus-25308 or errSecInteractionNotAllowed. I'm guessing this means I don't actually have access to my iPhone's keychain? Is there a way to allow access? Thanks for your time.

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  • Django DecimalField returns "None" instead of empty value

    - by Ed
    Is there a way to force django to display nothing instead of "None" for a Decimal Field that's been left blank? In my template, I show a list of all the values for a particular field. Each value is hyperlinked to a page that displays the results of a query filtered on that value. But because there are some entries with null value, my list includes actual DecimalField entries and "None" for all those that are empty. When a user clicks on None, django throws a validation error because you cannot query a DecimalField using a string. I could write if statements checking all instances of decimal fields for Nones and skipping them, but that is far from an elegant solution. Any advice? This is one part of the code, though there are other templates that derive the None value in slightly different manners: {% for item in choices %} <a href={% url app_views.field_choice item %}>{{ item }}</a><br> {% endfor %}

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  • Visual Studio error on valid SQL

    - by Sam
    I'm getting an annoying error in visual studio for SQL that executes fine. SELECT InvoiceLines.LineID, InvoiceLines.InvoiceID, InvoiceLines.Text, InvoiceLines.Rate, InvoiceLines.Count, InvoiceLines.Rate * InvoiceLines.Count AS LineTotal, ((InvoiceLines.Rate * InvoiceLines.Count) * (1 + Invoices.VatRate / 100)) * (1 - CAST(Invoices.Discount AS money) * InvoiceLines.ApplyDiscount / 100) AS LineTotalIncVat, InvoiceLines.ApplyDiscount FROM InvoiceLines LEFT JOIN Invoices ON Invoices.InvoiceID = InvoiceLines.InvoiceID What LineTotalIncVat is trying to do is compute the total for the invoice item while adding the vat and subtracting the discount, and yes, probably better to do this in code (would if I could) The error visual studio gives is: There was an error parsing the query [token line number =1, token line offset =14, token in error = InvoiceLines] Even though it will validate and execute without a problem in the query builder...

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  • What are good reasons to use explicit interface implementation for the sole purpose of hiding members?

    - by Nathanus
    During one of my studies into the intricacies of C#, I came across an interesting passage concerning explicit interface implementation. While this syntax is quite helpful when you need to resolve name clashes, you can use explicit interface implementation simply to hide more "advanced" members from the object level. The difference between allowing the use of object.method() or requiring the casting of ((Interface)object).method() seems like mean-spirited obfuscation to my inexperienced eyes. The text noted that this will hide the method from Intellisense at the object level, but why would you want to do that if it was not necessary to avoid name conflicts?

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  • How do I become a programmer and not some guy that can type some C?

    - by Phoxxent
    From what I understand, programming has a lot more to it than learning syntax, that it involves an understanding of what happens under-the-hood and even more. Currently, I am just a guy that can pump out a few loops in Python or C and maybe make a small-scope Zork clone as the hight of skill. So, what can I do to become an actual programmer? How can I find out what I need to know and learn it? I know this has been vaguely asked before, but I kind of want an answer of how as opposed to the whats that I have seen. Would it be nice to know how real programmers define being a programmer? yes. Is that going to actually help me (or anyone else) learn what they need to learn? no. (well, maybe.)

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  • Does SQL Server Compact Edition (SqlCe) have a SNAPSHOT table like Oracle Lite?

    - by MusiGenesis
    In Oracle Lite, you can create a SNAPSHOT table which is like a normal table except that it tracks changes to itself. The syntax is CREATE SNAPSHOT TABLE tblWhatever ... and you can perform CRUD operations on it like a normal table. To get the change information, you query the table like this: SELECT * FROM tblWhatever + WHERE ... which returns all the rows in the table (including deleted ones) meeting the WHERE clause, and you can access each row's row_state column as a normal field (which is invisible to a normal SELECT * FROM tblWhatever WHERE ... query). Is there some way to do the same thing with Sql Compact Edition (3.5) - i.e. create a table that tracks changes without using RDA?

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  • Point[] and Tri not "could not be found"

    - by Craig Dannehl
    Hi I'm trying to learn how to load a .obj file using OpenTK in windows Forms. I have seen a lot of examples out there, but I do see almost everyone uses List, and Point[]. Code example show these highlighted like there IDE know what these are; for example List<Tri> tris = new List<Tri>(); but mine just returns "The type or namespace name 'Tri' could not be found" is there an include I need to add or a using I am missing. Currently have this using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.IO; using System.Drawing; using OpenTK; using OpenTK.Graphics; using OpenTK.Graphics.OpenGL;

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  • Which numeral systems are useful in computer science?

    - by authchir
    I am wondering which numeral system different programmers are using, or would use if their language has support for them. As an example, in C++ we can use: Octal by prefixing with 0 (e.g. 0377) Decimal by default (e.g. 255) Hexadecimal by prefixing with 0x (e.g. 0xff) When working with bitmask, I am using hexadecimal but would sometimes want to be able to express binary numbers directly. I know some programming language support it with 0b syntax (e.g. 0b11111111). Is there any other numeric system useful in some computer science domain (e.g. cryptography, codecs, 3D graphics, etc)?

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  • How to combine two sql queries?

    - by plasmuska
    Hi Guys, I have a stock table and I would like to create a report that will show how often were items ordered. "stock" table: item_id | pcs | operation apples | 100 | order oranges | 50 | order apples | -100 | delivery pears | 100 | order oranges | -40 | delivery apples | 50 | order apples | 50 | delivery Basically I need to join these two queries together. A query which prints stock balances: SELECT stock.item_id, Sum(stock.pcs) AS stock_balance FROM stock GROUP BY stock.item_id; A query which prints sales statistics SELECT stock.item_id, Sum(stock.pcs) AS pcs_ordered, Count(stock.item_id) AS number_of_orders FROM stock GROUP BY stock.item_id, stock.operation HAVING stock.operation="order"; I think that some sort of JOIN would do the job but I have no idea how to glue queries together. Desired output: item_id | stock_balance | pcs_ordered | number_of_orders apples | 0 | 150 | 2 oranges | 10 | 50 | 1 pears | 100 | 100 | 1 This is just example. Maybe, I will need to add more conditions because there is more columns. Is there a universal technique of combining multiple queries together?

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  • SQL joining 3 tables when 1 table is emty

    - by AdRock
    I am trying to write a query that connects 3 tables. The first table is info about each festival The second table is the number of votes for each festival The third table is reviews for each festival I want to join all 3 tables so i get all the feilds from table1, join table1 with table2 on the festivalid but i also need to count the number of records in table 3 that applys to each festival. The first 2 tables give me a result becuase they both have data in them but table 3 is empty becuase there are no reviews yet so adding that to my query fives me no results SELECT f.*, v.total, v.votes, v.festivalid, r.reviewcount as count FROM festivals f INNER JOIN vote v ON f.festivalid = v.festivalid INNER JOIN (SELECT festivalid, count(*) as reviewcount FROM reviews) GROUP BY festivalid) as r on r.festivalid = v.festivalid

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  • How to make a non-english clone of CoffeeScript?

    - by Ans
    I want to make a non-english programming language that is identical to what CoffeeScript is to JavaScript. What I mean is that I don't want to build my own design or syntax. Just want to have a non-english programming language that compiles to JavaScript. I want to follow everything CoffeeScript fellows so I don't really want to make any design decisions. For example: This is coffeescript: number = 42 opposite = true number = -42 if opposite I want my language to be something like: ??? = 42 ??? = ???? ??? = -42 ??? ??? that get compiled to: var number, opposite; number = 42; opposite = true; if (opposite) { number = -42; }

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  • SQL: select random row from table where the ID of the row isn't in another table?

    - by johnrl
    I've been looking at fast ways to select a random row from a table and have found the following site: http://74.125.77.132/search?q=cache:http://jan.kneschke.de/projects/mysql/order-by-rand/&hl=en&strip=1 What I want to do is to select a random url from my table 'urls' that I DON'T have in my other table 'urlinfo'.The query I am using now selects a random url from 'urls' but I need it modified to only return a random url that is NOT in the 'urlinfo' table. Heres the query: SELECT url FROM urls JOIN (SELECT CEIL(RAND() * (SELECT MAX(urlid) FROM urls ) ) AS urlid ) AS r2 USING(urlid); And the two tables: CREATE TABLE urls ( urlid INT NOT NULL AUTO_INCREMENT PRIMARY KEY, url VARCHAR(255) NOT NULL, ) ENGINE=INNODB; CREATE TABLE urlinfo ( urlid INT NOT NULL PRIMARY KEY, urlinfo VARCHAR(10000), FOREIGN KEY (urlid) REFERENCES urls (urlid) ) ENGINE=INNODB;

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  • Can I combine values from multiple rows in another table into multiple columns of one row using SQL?

    - by Jordi
    I have two tables: T1: | M_ID | P_ID1 | P_ID2 | rest of T1 columns | | 0 | 0 | 1 | ... | | 1 | 2 | 3 | ... | T2: | P_ID | Type | A | B | | 0 | 1 | a | e | | 1 | 2 | b | f | | 2 | 1 | c | g | | 3 | 2 | d | h | Now, I want to have a query that selects this: | M_ID | P_1a | P_1b | P_2a | P_2b | rest of T1 columns | | 0 | a | e | b | f | ... | | 1 | c | g | c | h | ... | So, in words: I want to select all columns from T1, but I want to replace P_ID1 with the columns from T2, where the P_ID is equal to P_ID1, and the type is 1, and basically the same for P_ID2. I can obviously get the information I need with multiple queries, but I was wondering if there is a way that I can do this with one query. Any ideas? I'm currently using SQL Server 2008r2, but I'd also be interested in solutions for other database software. Thanks for the help!

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  • How to calculate change in ANSI SQL

    - by morpheous
    I have a table that contains sales data. The data is stored in a table that looks like this: CREATE table sales_data ( sales_time timestamp , sales_amt double ) I need to write parameterized queries that will allow me to do the following: Return the change in sales_amt between times t2 and t1, where t2 and t1 are separated by a time interval (integer) of N. This query will allow for querying for weekly changes in sales (for example). Return the change in change of sales_amt between times t2 and t1, and time t3 and t4. Thats is to calculate the value (val(t2)-val(t1)) - (val(t4)-val(t3)). where t2 and t1 are separated by the same time interval (interval N) as the interval between t4 and t3. This query will allow for querying for changes in weekly changes in sales (for example).

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  • codeigniter: how to redirect after login to current controller (php_self in regular php)

    - by krike
    Well it's not really a problem but I check if the user exist and log them in and redirect to site/members_area, but I don't want to send the user to a specific page but i want to reload the current controller. So if I login in index/home I would like to be redirected at index/home, how should I proceed? in regular php I would put in the action to redirect to current page <?php echo $_SERVER['PHP_SELF']; ?> This is the code in the framework function validate_credentials() { $this->load->model('membership_model'); $query = $this->membership_model->validate(); if($query) // if the user's credentials validated... { $data = array( 'username' => $this->input->post('username'), 'is_logged_in' => true ); $this->session->set_userdata($data); redirect('site/members_area'); //<-- this line here should be dynamic } else // incorrect username or password { $this->index(); } }

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  • mysql result set joining existing table

    - by Yang
    is there any way to avoid using tmp table? I am using a query with aggregate function (sum) to generate the sum of each product: the result looks like this: product_name | sum(qty) product_1 | 100 product_2 | 200 product_5 | 300 now i want to join the above result to another table called products. so that i will have a summary like this: product_name | sum(qty) product_1 | 100 product_2 | 200 product_3 | 0 product_4 | 0 product_5 | 300 i know 1 way of doing this is the dump the 1st query result to a temp table then join it with products table. is there a better way?

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  • Which tips helped you learn touch-typing? [closed]

    - by julien
    I've been learning touch-typing for about two weeks now, and I'm really commited to mastering this skill. Eventhough I'm doing ok with prose already, I'm struggling with programming syntax and even more with keybindings. Those stray you away from the home row more than regular words, and aren't as easy to practice. So I often hunt and peck in order to just get it out, but when reverting to old habits like this, I find it hard to get back into the touch-typing mindframe quickly. One little trick that has helped me so far when getting lost is to reposition every finger on its home row key, and mentally visualize the layout bias of the keyboard, ie the backslash kind of alignment of key columns. It's hard to describe though and probably a bit weird... Hope you guys have better tips !

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  • How do I select the number of distinct days in a date range?

    - by isme
    I'm trying to use the T-SQL function DATEDIFF to select the number of distinct dates in a time period. The following query: SELECT DATEDIFF(DAY, '2012-01-01 01:23:45', '2012-01-02 01:23:45') selects 1, which is one less than I want. There are two distinct dates in the range: 2012-01-01 and 2012-01-02. It is not correct to add one to the result in the general case. The following query: SELECT DATEDIFF(DAY, '2012-01-01 00:00:00', '2012-01-02 00:00:00') selects 1, which is correct, because there is only one distinct date in the range. I'm sure there is a simple bit of arithmetic that I'm missing to calculate this. Can someone help me?

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  • Rendering a variable with erb.

    - by TZer0
    I've got the following problem: I have rhtml (html minced together with ruby inside <% % and <%= % tags) stored in a database which I want to render. The information is acquired through a query. I need to be able to evaluate the information I get from the database as though as it was normal content inside the .erb-file. What I currently have: <% @mymods.each do |mod| %> <%= render_text(mod["html"])%> <% end %> Where mod["html"] is the variable containing the rhtml-code and @mymods an array of objects from the query. I have currently no idea what function I should use (render_text does, of course, not work). Help is greatly appreciated. /TZer0

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