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• Google App Engine - Dealing with concurrency issues of storing an object

  - by Spines

  My User object that I want to create and store in the datastore has an email, and a username. How do I make sure when creating my User object that another User object doesn't also have either the same email or the same username? If I just do a query to see if any other users have already used the username or the email, then there could be a race condition. UPDATE: The solution I'm currently considering is to use the MemCache to implement a locking mechanism. I would acquire 2 locks before trying to store the User object in the datastore. First a lock that locks based on email, then another that locks based on username. Since creating new User objects only happens at user registration time, and it's even rarer that two people try to use either the same username or the same email, I think it's okay to take the performance hit of locking. I'm thinking of using the MemCache locking code that is here: http://appengine-cookbook.appspot.com/recipe/mutex-using-memcache-api/ What do you guys think?

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• javax.persistence.NoResultException: getSingleResult() did not retrieve any entities

  - by apple1988

  Hello, i have created a namedquery with ejb to check if the username is used. When the singleResult is null, then i get the following Exception : javax.persistence.NoResultException: getSingleResult() did not retrieve any entities But this exception is the result that i want when the username is free. ^^ Here is the code: public User getUserByUsername(String username) throws DAOException{ try{ Query q = em.createNamedQuery(User.getUserByUsername); q.setParameter("username", username); return (User) q.getSingleResult(); }catch(Exception e){ throwException(username, e); return null; } } Does anybody know what the problem is. :( I will return null andy don`t get an Exception. Thank you very much

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• HQL multiple updates. Is there a better way?

  - by folone

  I have a Map, that I want to persist. The domain object is something like this: public class Settings { private String key; private String value; public String getKey() { ... } public String getValue() { ... } public void setKey() { ... } public void setValue() { ... } } The standard approach is to generate a Setting for each pair, and saveOrUpdate() it. But it generates way too much queries, because I need to save lots of settings at a time, and it really affects perfomance. Is there a way to do this using one update query?

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• How much Stored Procedures created everyday ?

  - by Space Cracker

  I make a query that return to me the count of Stored Procedure that created everyday as follow SELECT convert(varchar, crdate, 103) as Date,Count(*) as Counter FROM sysobjects WHERE (xtype = 'p') AND (name NOT LIKE 'dt%') Group by convert(varchar, crdate, 103) and its already work but dates appear in string format that i can't order it such as below 01/03/2010 3 01/04/2008 4 01/05/2010 5 01/11/2008 1 01/12/2008 4 02/03/2008 1 02/03/2010 2 02/04/2008 4 02/05/2010 2 02/11/2008 2 02/11/2009 2 02/12/2008 4 03/01/2010 1 03/02/2010 2 03/03/2010 2 03/04/2008 2 03/04/2010 2 03/05/2008 1 03/05/2010 2 I want to make that in which date is in datetime format that i can make order by successfully, i tried convert(datetime, crdate, 103) but it show Full date any idea of how to do ?

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• Why is String final in Java?

  - by Alex

  From when I learned that the class java.lang.String is declared as final in Java, I was wondering why is that? I didn't find any answer back then, but this post: How to create a replica of String class in Java? reminded me of my query. Sure, String provides all the functionality I ever needed, and never thought of any operation that would require an extension of class String, but still you'll never know what someone might need! So, does anyone know what was the intent of the designers when they decided to make it final? See also: Why is String a sealed class in C#?

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• Android: Width and Height of View After Orientation Change

  - by David

  I need to get the width and height of a WebView and pass them in the query string of the URL I am loading in the WebView. I have found a way to do this in onResume(). Since the width and height are not calculated at this point, I post a Runnable to the WebView to be queued for after the UI loads. Here's my problem: when the orientation changes, I am handling it in onConfigurationChanged. When I try to post a Runnable in onConfigurationChanged to the WebView, the WebView's width and height end up being the old orientation's width and height. At what point can I intercept the new width and height after orientation change?

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• ASP.NET MVC: Is is possible to set a global variable?

  - by Sergio

  Hello, I have a process within my MVC 2 application that takes a large amount of time and alters many rows in the database in the process. There is a chance that two or more users could attempt to perform this action at the same time, which would lead to undesirable effects. Is there a way to set a global flag somewhere within asp.net that I can check against all requests to see if the action in question is currently being executed? (a bit that I flip prior to running query, and then then flip back on completition) Or is there a better way of handling this situation? Thanks

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• What's the correct way to stop a background process on Mac OS X?

  - by mcsheffrey

  I have an application with 2 components: a desktop application that users interact with, and a background process that can be enabled from the desktop application. Once the background process is enabled, it will run as a user launch agent independently of the desktop app. However, what I'm wondering is what to do when the user disables the background process. At this point I want to stop the background process but I'm not sure what the best approach is. The 3 options that I see are: Use the 'kill' command. Direct, but not reliable and just seems somewhat "wrong". Use an NSMachPort to send an exit request from the desktop app to the background process. This is the best approach I've thought of but I've run into an implementation problem (I'll be posting this in a separate query) and I'd like to be sure that the approach is right before going much further. Something else??? Thank you in advance for any help/insight that you can offer.

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• How do I request a single random row from a force.com database in SOQL?

  - by Ollie C

  Total row-count is in the range 10k-100k rows. Can I use RAND() on force.com? Unfortunately although all the rows have a unique numeric identifier, there are many gaps, and I'd often want to select a random row from a filtered subset anyway. I suspect there's no particularly efficient way to do this, but is it possible at all? Ultimately all I want to do is to extract one row from a table (or a subset based on specific filter criteria) at random. If force.com doesn't let me select a random row, then can I query the rows to select from, and assign sequential IDs to all the rows, say 1-1,035, and then select a random number in that range locally, say 349, and then get row 349?

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• Convert the code from PHP to Ruby on rails

  - by theband

  public function getFtime() { $records=array(); $sql="SELECT * FROM `finishedtime`"; $result=mysql_query($sql); if(!$result){throw new Exception(mysql_error());} if(mysql_num_rows($result)==0){return $records;} while($row=mysql_fetch_assoc($result)){$records[]=$row;} return $records; } I am in the process of learning Ruby, can anyone convert this code into Ruby. This will make me construe on how to run a query and thrown the fetched result back.

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• Php/ODBC encoding problem

  - by JohnM2

  I use ODBC to connect to SQL Server from PHP. In PHP I read some string (nvarchar column) data from SQL Server and then want to insert it to mysql database. When I try to insert such value to mysql database table I get this mysql error: Incorrect string value: '\xB3\xB9ow...' for column 'name' at row 1 For string with all ASCII characters everything is fine, the problem occurs when non-ASCII characters (from some European languages) exist. So, in more general terms: there is a Unicode string in MS SQL Server database, which is retrieved by PHP trough ODBC. Then it is put in sql insert query (as value for utf-8 varchar column) which is executed for mysql database. Can someone explain to me what is happening in this situation in terms of encoding? At which step what character encoding convertions may take place? I use: PHP 5.2.5, MySQL5.0.45-community-nt, MS Sql Server 2005.

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• Django: text fixture fails to load

  - by Esteban Feldman

  Hi all, Did a dumpdata of my project, then in my new test I added it to fixtures. from django.test import TestCase class TestGoal(TestCase): fixtures = ['test_data.json'] def test_goal(self): """ Tests that 1 + 1 always equals 2. """ self.failUnlessEqual(1 + 1, 2) When running the test I get: Problem installing fixture 'XXX/fixtures/test_data.json': DoesNotExist: XXX matching query does not exist. But manually doing loaddata works fine does not when the db is empty. I do a dropdb, createdb a simple syncdb the try loaddata and it fails, same error. Any clue? Python version 2.6.5, Django 1.1.1

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• Django: order by count of a ForeignKey field?

  - by AP257

  This is almost certainly a duplicate question, in which case apologies, but I've been searching for around half an hour on SO and can't find the answer here. I'm probably using the wrong search terms, sorry. I have a User model and a Submission model. Each Submission has a ForeignKey field called user_submitted for the User who uploaded it. class Submission(models.Model): uploaded_by = models.ForeignKey('User') class User(models.Model): name = models.CharField(max_length=250 ) My question is pretty simple: how can I get a list of the three users with the most Submissions? I trued creating a num_submissions method on the User model: def num_submissions(self): num_submissions = Submission.objects.filter(uploaded_by=self).count() return num_submissions and then doing: top_users = User.objects.filter(problem_user=False).order_by('num_submissions')[:3] but this fails, as do all the other things I've tried. Can I actually do it using a smart database query? Or should I just do something more hacky in the views file?

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• Access Codeigniter database functions from file

  - by Manny Calavera

  Hello. I am using a SWFupload script and I can't make a request from flash with mod_rewrite, I don't know why... I just need to point the Flash request to that file directly. This file runs an upload script that works ok but now I need to save some info to the database and I would like to know what should I write to have access from that file that is not called from the controller and does not extend the model in order to run a mysql query. Thanks.

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• How to delete refClass record in Doctrine?

  - by terrani

  Hi all! I have many-to-many relations with the following tables. post tag post_tag I created three classes with Doctrine, so I have the following classes as well. BasePost BaseTag BasePostTag in the setUp() method, I defined relations. I like to delete tag record when I delete post record. So I simply put cascade as descirbed on Doctrine document. $this->hasMany("Tag as Tags",array( 'refClass' => 'PostTag', 'local'=>'object_id', 'foreign'=>'tag_id', 'cascade'=> array('delete') )); it works without a problem. My questions is, how do I delete a record from post_tag table? Do I need to create a query myself?

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• Not able to send POST request through jQuery Ajax

  - by Amit

  Hi, I was trying to send an ajax request as POST request. But when i verified it on httpFox on firefox, the request is sent as GET. I tried pbht $.ajax() and $.post(). Many had a query regarding the same and had missed the "type" in $.ajax(), but even if i mention the type as "POST", the request will be of type GET. Here is my code: $('.test').click(function(){ alert("clicked"); $.ajax({ type: "POST", url: "www.testsite.com", data: "name=John&location=Boston", success: function(msg){ alert( "Data Saved: " + msg ); } }); }); Any idea why it happens?

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• linq "let" translation

  - by luke

  I understand that when the C# compiler sees a linq query comprehension, it basically does a straight translation to the corresponding Linq Extension methods and lambdas. i.e. from x in list select x.property gets translated to: list.Select(x => x.property) my question is what do let clauses get translated to. for example how would this get translated by the compiler. from x in list let v = SomeComplexExpressionDependingOnx select v (p.s. i know this could be reduced to just select SomeComplexExpressionDependingOnx but i want to know how this is done in general) Thanks!

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• PHP & MySQL form question.

  - by peakUC

  How do I allow all users to have there username field empty without having them to enter a username when they submit the form using PHP and MySQL? Here is part my PHP and MySQL code. $username = mysqli_real_escape_string($mysqli, $purifier->purify(htmlentities(strip_tags($_POST['username'])))); if(isset($_POST['username'])) { // Make sure the username address is available: $u = "SELECT * FROM users WHERE username = '$username' AND user_id <> '$user_id'"; $r = mysqli_query ($mysqli, $u) or trigger_error("Query: $q\n<br />MySQL Error: " . mysqli_error($mysqli)); if (mysqli_num_rows($r) == TRUE) { // Unavailable. echo '<p class="error">Your username is unavailable!</p>'; $username = NULL; } else if(mysqli_num_rows($r) == 0) { // Available. $username = mysqli_real_escape_string($mysqli, $purifier->purify(htmlentities(strip_tags($_POST['username'])))); } }

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• How to get number of rows deleted from mysql in shell script

  - by simonlord

  Hi all I can't work out how to get the mysql client to return the number of rows deleted to the shell when running a delete. Does anyone know what option will enable this? Or ways around it? Here's what i'm trying, but i get no output: #!/bin/bash deleted=`mysql mydb -e "delete from mytable where insertedtime < '2010-04-01 00:00:00'"|tail -n 1` I was expecting something like this as the output from mysql: deleted 999999 Which is why i have the tail -n 1 so i only pick up the count and not the column name. When running the command by hand (mysql mydb -e "delete from mytable where insertedtime < '2010-04-01 00:00:00'") there is no output. When running the command interactively when running the mysql client i ge the following: mysql>delete from mytable where insertedtime < '2010-04-01 00:00:00'; Query OK, 0 rows affected (0.00 sec) I want to get the rows affected count into my shell variable. Any help would be most appreciated.

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• Get the last N rows in the database in order?

  - by Kristopher

  Let's say I have the following database table: record_id | record_date | record_value -----------+-------------+-------------- 1 | 2010-05-01 | 195.00 2 | 2010-07-01 | 185.00 3 | 2010-09-01 | 175.00 4 | 2010-05-01 | 189.00 5 | 2010-06-01 | 185.00 6 | 2010-07-01 | 180.00 7 | 2010-08-01 | 175.00 8 | 2010-09-01 | 170.00 9 | 2010-10-01 | 165.00 I want to grab the last 5 rows with the data ordered by record_date ASC. This is easy to do with: SELECT * FROM mytable ORDER BY record_date ASC LIMIT 5 OFFSET 4 Which would give me: record_id | record_date | record_value -----------+-------------+-------------- 6 | 2010-07-01 | 180.00 7 | 2010-08-01 | 175.00 3 | 2010-09-01 | 175.00 8 | 2010-09-01 | 170.00 9 | 2010-10-01 | 165.00 But how do I do this when I don't know how many records there are and can't compute the magic number of 4? I've tried this query, but if there are less than 5 records, it results in a negative OFFSET, which is invalid: SELECT * FROM mytable ORDER BY record_date ASC LIMIT 5 OFFSET (SELECT COUNT(*) FROM mytable) - 5; So how do I accomplish this?

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• mysql ignores not null constraint?

  - by Marga Keuvelaar

  I have created a table with NOT NULL constraints on some columns in MySQL. Then in PHP I wrote a script to insert data, with an insert query. When I omit one of the NOT NULL columns in this insert statement I would expect an error message from MySQL, and I would expect my script to fail. Instead, MySQL inserts empty strings in the NOT NULL fields. In other omitted fields the data is NULL, which is fine. Could someone tell me what I did wrong here? I'm using this table: CREATE TABLE IF NOT EXISTS tblCustomers ( cust_id int(11) NOT NULL AUTO_INCREMENT, custname varchar(50) NOT NULL, company varchar(50), phone varchar(50), email varchar(50) NOT NULL, country varchar(50) NOT NULL, ... date_added timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (cust_id) ) ; And this insert statement: $sql = "INSERT INTO tblCustomers (custname,company) VALUES ('".$customerName."','".$_POST["CustomerCompany"]."')"; $res = mysqli_query($mysqli, $sql);

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• FieldError when annotating over foreign keys

  - by X_9

  I have a models file that looks similar to the following: class WithDate(models.Model): adddedDate = models.DateTimeField(auto_now_add=True) modifiedDate = models.DateTimeField(auto_now=True) class Meta: abstract = True class Match(WithDate): ... class Notify(WithDate): matchId = models.ForeignKey(Match) headline = models.CharField(null=True, blank=True, max_length=10) For each Match I'm trying to get a count of notify records that have a headline. So my call looks like matchObjs = Match.objects.annotate(notifies_made=Count('notify__headline__isnull')) This keeps throwing a FieldError. I've simplified the query down to matchObjs = Match.objects.annotate(notifies_made=Count('notify')) And I still get the same FieldError... I've seen this work in other cases (other documentation, other SO questions like this one) but I can't figure out why I'm getting an error. The specific error that is returned is as follows: Cannot resolve keyword 'notify' into field. Choices are: (all fields from Match model) Does anyone have a clue as to why I can't get this annotation to work across tables? I'm baffled after looking at the other SO question and various Django docs where I've seen this done. Edit: I am using Django 1.1.1

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• Java source code generation frameworks

  - by Superfilin

  I have a set of Java 5 source files with old-style Doclet tags, comments and annotations. And based on that I would like to write a generator for another set of Java classes. What is the best way to do that? And are there any good standalone libraries for code analysis/generation in Java? Any shared exprience in this field is appreciated. So, far I have found these: JaxME's Java Source Reflection - seems good, but it does not seem to support annotations. Also it had no release since 2006. Annogen - uses JDK's Doclet generator, which has some bugs under 1.5 JDK. Also it had no releases for a long time. Javaparser - seems good as well and pretty recent, but only supports Visitor pattern for a single class i.e. no query mechanism like in the 2 above packages.

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• Find overdrawn accounts in SQL

  - by mazzzzz

  Hey guys, I have a program that allows me to run queries against a large database. I have two tables that are important right now, Deposits and withdraws. Each contains a history of every user. I need to take each table, add up every deposit and withdraws (per user), then subtract the withdraws from the deposits. I then need to return every user whos result is negative (aka they withdrew more then they deposited). Is this possible in one query? Example: Deposit Table: |ID|UserName|Amount| |1 | Use1 |100.00| |2 | Use1 |50.00 | |3 | Use2 |25.00 | |4 | Use1 | 5.00 | WithDraw Table: |ID|UserName|Amount| |2 | Use2 | 5.00 | |1 | Use1 |100.00| |4 | Use1 | 5.00 | |3 | Use2 |25.00 | So then the result would output: |OverWithdrawers| | Use2 | Is this possible (I sure don't know how to do it)? Thanks for any help, Max

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• How to retrieve the ordered list of best articles having a minimum number of votes by using HSQL ?

  - by fabien7474

  I have a Vote domain class from my grails application containing properties like article_id and note I want to HQL query the Vote domain class in order to retrieve the 5 best rated articles having at least 10 votes. I tried : SELECT v.article_id, avg(v.note), count(*) FROM vote v where count(*) >= 10 group by v.article_id order by avg(v.note) desc limit 5; But unfortunately the insertion of where count(*) >= 10 throws an error. How can I do that in a simple way? Thank you for your help.

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