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• How can I get data off of a damaged thumb drive?

  - by Lord Torgamus

  A guy I work with just came by to ask me about a damaged thumb drive/USB flash drive. Apparently his son dropped it on a hard surface and it won't power up anymore. They've tried plugging it into multiple machines without success, even though each port they tried was able to power other USB devices. He knows it's not a lost cause because a local tech store is offering to recover the data for $500, but he says they're not worth that much. I figured someone on SU would have an idea about this; he doesn't care about using the drive in the future, just wants to salvage a few files that would be a pain to recreate. Is this possible without advanced equipment, and if so, how? He said he already tried the advice on the Internet about typing in different drive letters and such, but that failed because there was no power going to the drive. He also said that he opened the case up at one point, but I'm not sure what, if anything, he did inside.

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• Error in connection in ruby.

  - by piemesons

  require 'rubygems' require 'mysql' db = Mysql.connect('localhost', 'root', '', 'mohit') //db.rb:4: undefined method `connect' for Mysql:Class (NoMethodError) //undefined method `real_connect' for Mysql:Class (NoMethodError) db.query("CREATE TABLE people ( id integer primary key, name varchar(50), age integer)") db.query("INSERT INTO people (name, age) VALUES('Chris', 25)") begin query = db.query('SELECT * FROM people') puts "There were #{query.num_rows} rows returned" query.each_hash do |h| puts h.inspect end rescue puts db.errno puts db.error end error i am geting is: undefined method `connect' for Mysql:Class (NoMethodError) OR undefined method `real_connect' for Mysql:Class (NoMethodError) EDIT return value of Mysql.methods ["private_class_method", "inspect", "name", "tap", "clone", "public_methods", "object_id", "__send__", "method_defined?", "instance_variable_defined?", "equal?", "freeze", "extend", "send", "const_defined?", "methods", "ancestors", "module_eval", "instance_method", "hash", "autoload?", "dup", "to_enum", "instance_methods", "public_method_defined?", "instance_variables", "class_variable_defined?", "eql?", "constants", "id", "instance_eval", "singleton_methods", "module_exec", "const_missing", "taint", "instance_variable_get", "frozen?", "enum_for", "private_method_defined?", "public_instance_methods", "display", "instance_of?", "superclass", "method", "to_a", "included_modules", "const_get", "instance_exec", "type", "<", "protected_methods", "<=>", "class_eval", "==", "class_variables", ">", "===", "instance_variable_set", "protected_instance_methods", "protected_method_defined?", "respond_to?", "kind_of?", ">=", "public_class_method", "to_s", "<=", "const_set", "allocate", "class", "new", "private_methods", "=~", "tainted?", "__id__", "class_exec", "autoload", "untaint", "nil?", "private_instance_methods", "include?", "is_a?"] return value of Mysql.methods(false) is []... blank array

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• JPA/Hibernate Parent/Child relationship

  - by NubieJ

  Hi I am quite new to JPA/Hibernate (Java in general) so my question is as follows (note, I have searched far and wide and have not come across an answer to this): I have two entities: Parent and Child (naming changed). Parent contains a list of Children and Children refers back to parent. e.g. @Entity public class Parent { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "PARENT_ID", insertable = false, updatable = false) private int id; /* ..... */ @OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.LAZY) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID", nullable = true) private Set<child> children; /* ..... */ } @Entity public class Child { @Id @Basic @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name = "CHILD_ID", insertable = false, updatable = false) private int id; /* ..... */ @ManyToOne(cascade = { CascadeType.REFRESH }, fetch = FetchType.EAGER, optional = false) @JoinColumn(name = "PARENT_ID", referencedColumnName = "PARENT_ID") private Parent parent; /* ..... */ } I want to be able to do the following: Retrieve a Parent entity which would contain a list of all its children (List), however, when listing Parent (getting List, it of course should omit the children from the results, therefore setting FetchType.LAZY. Retrieve a Child entity which would contain an instance of the Parent entity. Using the code above (or similar) results in two exceptions: Retrieving Parent: A cycle is detected in the object graph. This will cause infinitely deep XML... Retrieving Child: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xxxxxxxxxxx, no session or session was closed When retrieving the Parent entity, I am using a named query (i.e. calling it specifically) @NamedQuery(name = "Parent.findByParentId", query = "SELECT p FROM Parent AS p LEFT JOIN FETCH p.children where p.id = :id") Code to get Parent (i.e. service layer): public Parent findByParentId(int parentId) { Query query = em.createNamedQuery("Parent.findByParentId"); query.setParameter("id", parentId); return (Parent) query.getSingleResult(); } Why am I getting a LazyInitializationException event though the List property on the Parent entity is set as Lazy (when retrieving the Child entity)?

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• Best practice accessing an array set within a class

  - by user350599

  I have created a basic class for a customer. I haven't done this before and want to know the best way to access the data. Should I have a get() method for every field in the customer array or should I simply pass the customer array back and access with the page. i.e. Just return the array class Customer { protected $id; protected $customer; public function __construct($customer_id) { $this->id = $customer_id; $this->set_customer(); } protected function set_customer() { $query = mysql_query("SELECT * FROM customer WHERE id = '$this->id'"); $this->customer = mysql_fetch_row($query); } public function get_customer() { return $this->customer; } } versus create a method for each item in the array class Customer { protected $id; protected $customer; public function __construct($customer_id) { $this->id = $customer_id; $this->set_customer(); } protected function set_customer() { $query = mysql_query("SELECT * FROM customer WHERE id = '$this->id'"); $this->customer = mysql_fetch_row($query); } public function get_customer_name() { return $this->customer->customer_name; } ... ... } versus option 3 based on Tobias' feedback: (not sure if syntax is correct) class Customer { protected $id; protected $customer; public function __construct($customer_id) { $this->id = $customer_id; return $this->set_customer(); } protected function set_customer() { $query = mysql_query("SELECT * FROM customer WHERE id = '$this->id'"); return mysql_fetch_row($query); } }

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• The question about the basics of LINQ to SQL working

  - by Alex

  I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance. I used to think that when doing LINQ queries like from Customer in DB.Customers where Customer.Age > 30 select Customer Get all customers from the database ("SELECT * FROM Customers"), move them to the Customers array and then make a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application. Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string SELECT * FROM Customers WHERE Age > 30 And only when necessary it will run the query. So my question is: am I right? And when is the query actually run? The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem. I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query: from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books: var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID; BUT when I try to do the query now: from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?

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• Computer powers off then tries to start up but resets repeatedly.

  - by Sam Holder

  My machine has started shutting itself off after a few minutes on, everything goes off. A few seconds (3-5) after everything has stopped the lights come back on, the cpu fan and gfx card come on again. They spin for a second, then everything goes off again. A few seconds later same things happens again, light come back on, fans spin for a few seconds then go off. This repeats seemingly forever. If I leave it for a while I can power the machine back on for a while and it will boot again. It will then stay on for a little while again before power off. Rinse and repeat. Is this likely to be power supply or something else? The machine has been up and running for a couple of years before this.

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• Is it safe to operate a laptop without battery?

  - by leladax

  I know it's 'unsafe' in terms of data loss but I noticed motherboards still have some of their circuits on power when they are plugged in [e.g. a circuit that must wait for power-on signals is certainly one of them]. Hence, I wondered if it would increase the life of the laptop if the battery was simply off. Let alone that may also increase battery life, but that's the least of my concerns. Notice the main point is to plug it off on hibernate and have no power source whatsoever for the duration of being off (apart from the clock battery). (i.e. saving having to plug off the battery every time)

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• Linq. Help me tune this!

  - by dtrick

  I have a linq query that is causing some timeout issues. Basically, I have a query that is returning the top 100 results from a table that has approximately 500,000 records. Here is the query: using (var dc = CreateContext()) { var accounts = string.IsNullOrEmpty(searchText) ? dc.Genealogy_Accounts .Where(a => a.Genealogy_AccountClass.Searchable) .OrderByDescending(a => a.ID) .Take(100) : dc.Genealogy_Accounts .Where(a => (a.Code.StartsWith(searchText) || a.Name.StartsWith(searchText)) && a.Genealogy_AccountClass.Searchable) .OrderBy(a => a.Code) .Take(100); return accounts.Select(a => } } Oddly enough it is the first linq query that is causing the timeout. I thought that by doing a 'Take' we wouldn't need to scan all 500k of records. However, that must be what is happening. I'm guessing that the join to find what is 'searchable' is causing the issue. I'm not able to denormalize the tables... so I'm wondering if there is a way to rewrite the linq query to get it to return quicker... or if I should just write this query as a Stored Procedure (and if so, what might it look like). Thanks.

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• Computer hangs on start-up, but re-start always works

  - by user10604

  I press the power switch; the fans start whirring; then precisely nothing happens. The monitor lights (I have two monitors) blink to indicate that they aren't receiving any signal - no BIOS splash screen, nothing. This scenario occurs about 80 percent of the time, the other 20 percent being normal starts. Noticing that the computer has not started properly, I press the power switch for four seconds to turn the computer off, and then I press it again to start the computer for the second time. It always starts normally the second time. Always. The power supply is a 750W from SilverStone. The motherboard is a Gigabyte P55A-UD3P. The video card is an Asus EN9800GT. There's 8 GB of RAM. I don't know what other information might be pertinent. Help!

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• Paginating requests to an API

  - by user332912

  I'm consuming (via urllib/urllib2) an API that returns XML results. The API always returns the total_hit_count for my query, but only allows me to retrieve results in batches of, say, 100 or 1000. The API stipulates I need to specify a start_pos and end_pos for offsetting this, in order to walk through the results. Say the urllib request looks like "http://someservice?query='test'&start_pos=X&end_pos=Y". If I send an initial 'taster' query with lowest data transfer such as http://someservice?query='test'&start_pos=1&end_pos=1 in order to get back a result of, for conjecture, total_hits = 1234, I'd like to work out an approach to most cleanly request those 1234 results in batches of, again say, 100 or 1000 or... This is what I came up with so far, and it seems to work, but I'd like to know if you would have done things differently or if I could improve upon this: hits_per_page=1000 # or 1000 or 200 or whatever, adjustable total_hits = 1234 # retreived with BSoup from 'taster query' base_url = "http://someservice?query='test'" startdoc_positions = [n for n in range(1, total_hits, hits_per_page)] enddoc_positions = [startdoc_position + hits_per_page - 1 for startdoc_position in startdoc_positions] for start, end in zip(startdoc_positions, enddoc_positions): if end total_hits: end = total_hits print "url to request is:\n ", print "%s&start_pos=%s&end_pos=%s" % (base_url, start, end) p.s. I'm a long time consumer of StackOverflow, especially the Python questions, but this is my first question posted. You guys are just brilliant.

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• Dividing numbers between rows in MySQL + PHP

  - by André Figueira

  Hi I am working on a kind of raffle system which divides 1 million random numbers into an x amount of tickets, e.g. 1 million random numbers to 10,000 tickets. Each ticket is a row in a database, we then have another table ticket numbers in which i need to give 100 numbers to each ticket they are related by the ticket id. So at the moment this is my code: //Amount of the 1 million tickets divided to the tickets $numbersPerTickets = $_POST['numbersPerTicket']; //The total cost of the property $propertyPrice = $_POST['propertyPrice']; //The total amount of tickets $totalTickets = NUMBER_CIELING / $numbersPerTickets; //The ticket price $ticketPrice = $propertyPrice / $totalTickets; //Generate array with random numbers up to 999,999 $randomTicketNumbers = createTicketNumbers(); //Creation loop counter $ticketCreationCount = 1; //Loop and create each ticket while($ticketCreationCount <= $totalTickets) { //Create a padded ticket number $ticketNumber = str_pad($ticketCreationCount, 6, 0, STR_PAD_LEFT); $query = ' INSERT INTO tickets( propertyID, ticketNumber, price ) VALUES( "'.$propertyID.'", "'.$ticketNumber.'", "'.$ticketPrice.'" ) '; $db->query($query); //Get the ID of the inserted ticket to use to insert the ticket numbers $ticketID = $db->insert_id; $loopBreak = $numbersPerTickets; $addedNumberCount = 1; foreach($randomTicketNumbers as $key => $value) { $query = ' INSERT INTO ticketNumbers( ticketID, number ) VALUES( "'.$ticketID.'", "'.$value.'" ) '; $db->query($query); unset($randomTicketNumbers[$key]); if($addedNumberCount == $loopBreak){ break; }else{ $addedNumberCount++; } } $ticketCreationCount++; } But this isn't working it adds the right amount of tickets, which in the case for testing is 10,000 but then adds far too many ticket numbers, it ends up exceeding the million numbers in the random tickets array, The random tickets array is just a simple 1 tier array with 1 million numbers sorted randomly.

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• How to properly set CPU Units for OpenVz VEs

  - by gucki

  According to all the sources I read (openvz wiki, various mailinglists, forums, ..) the values of the cpuunits settings are relative to each other. So when all are equal and the system is busy, all receive the same cpu share. But something still puzzles me with that: why is there a tool "vzcpucheck" which shows "the power of the node/ host": Current CPU utilization: 18000 Power of the node: 880001 Why is there (do I need) an absolute number when all settings are only relative? Shouldn't those two settings result in exactly the same? ve1: 1 ve2: 1 ve3: 1 = 3 ve1: 293334 ve1: 293334 ve1: 293334 = 880001 (power of the node) What's the difference?

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• Motherboard or Processor Problem

  - by bradlis7

  My computer is broken, but I'm having trouble narrowing down the issue. I replaced the power supply, because I assumed that was the issue, but it has the same problem. The issue started with my computer starting the fans and running, but it didn't get to the BIOS screen for about 10 seconds. Now it refuses to do anything when the power button is pressed, except when I turn off the machine and take the processor out for 10-20 seconds, then put it back in, I came hit the power button immediately, and the fans start for 1/2 second, and quit. Does this sound like a is a processor or motherboard issue? I removed all components, so I know that the issue is with one of these two things.

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• How can I prevent my computer from waking up accidentally?

  - by Ivo Flipse

  When I put my computer into sleep mode, it will wake up while I'm away from it. There's nothing near the computer that could move the mouse or accidentally press a button and I have no idea what might be causing it. I tried checking what woke it, apparently LASTWAKE only tells me that it has been in sleep mode, not what woke it up. I also couldn't find anything in my Power Options regarding Sleep that seems off. Poking around in the Event Viewer I notice the following: The Power-Troubleshooter event at the top notes the following: The system has returned from a low power state. Sleep Time: ?2012?-?10?-?27T11:31:53.408927000Z Wake Time: ?2012?-?10?-?27T12:25:51.887029300Z Wake Source: Unknown So does anyone have an idea to find out what might be causing it and how I can prevent my computer from randomly waking up?

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• Qt XQuery into a QStringList

  - by Stewart

  Hi, I'm trying to use QtXmlQuery to extract some data from XML. I'd like to put this into a QStringList. I try the following: QByteArray in = "this is where my xml lives"; QBuffer received; received.setData(in); received.open(QIODevice::ReadOnly); QXmlQuery query; query.bindVariable("data", &received); query.setQuery(NAMESPACE //contains definition of the t namespace "doc($data)//t:service/t:serviceID/text()"); QBuffer outb; outb.open(QIODevice::ReadWrite); QXmlSerializer s(query, &outb); query.evaluateTo(&s); qDebug() << "buffer" << outb.data(); //This works perfectly! QStringList * queryResult = new QStringList(); query.evaluateTo(queryResult); qDebug() << "string list" << *queryResult; //This gives me no output! As you can see, everything works fine when I send the output into a QBuffer via a QXmlSerializer... but I get nothing when I try to use a QStringList.

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• Why is only 2 of my querys working? (PHP/Mysql)

  - by ggfan

  When I remove a posting, I want it to remove the posting itself, any comments related to it, and like/dislike of the comments, and favorites that people added. So there are 4 queries that do this, but somehow only 2 of the 4 are working. When I switch say query 2 for query 3, then query 2 works and query 3 doesn't... The table names are correct and it is getting the data via $_GET. // Grab the data from the GET $posting_id = $_GET['posting_id']; // Delete the posting from the database $query = "DELETE FROM posting WHERE posting_id=$posting_id LIMIT 1"; mysqli_query($dbc, $query) or die(mysql_error()); // Delete the comments $query2 = "DELETE FROM comments WHERE posting_id=$posting_id "; mysqli_query($dbc, $query2) or die(mysql_error()); // Delete the like/dislike $query3 = "DELETE FROM comment_likedislike WHERE posting_id=$posting_id "; mysqli_query($dbc, $query3) or die(mysql_error()); // Delete the favorites $query4 = "DELETE FROM favorite WHERE posting_id=$posting_id "; mysqli_query($dbc, $query4) or die(mysql_error());

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• Passing arguments and conditions to model in codeigniter

  - by stormdrain

  I'm adding some models to a project, and was wondering if there is a "best practice" kind of approach to creating models: Does it make sense to create a function for each specific query? I was starting to do this, then had the idea of creating a generic function that I could pass parameters to. e.g: Instead of function getClients(){ return $this->db->query('SELECT client_id,last FROM Names ORDER BY id DESC'); } function getClientNames($clid){ return $this->db->query('SELECT * FROM Names WHERE client_id = '.$clid); } function getClientName($nameID){ return $this->db->query('SELECT * FROM Names WHERE id ='.$nameID); } } Something like function getNameData($args,$cond){ if($cond==''){ $q=$this->db->query('SELECT '.$args.' FROM Names'); return $q; }else{ $q=$this->db->query('SELECT '.$args.' FROM Names WHERE '.$cond); return $q; } } where I can pass the fields and conditions (if applicable) to the model. Is there a reason the latter example would be a bad idea? Thanks!

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• Need a design approach or suggestion for a simple structure using Servlet.

  - by akshay

  Hi I have to design such that whenever user pass a query I process it using servlet and then call the js page to draw the chart 1 user writes a query on a page 2 the page call the servelt class public class MyServlet extends Httpservlet implements DataSourceServlet {..... return data The user see a beautiful string like this.. google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); 3 when the user hits on different html page myhtml.js it draws the chart. I want the Myservlet class itself call the myhtml.js page and draw the chart directly. and want to eliminate the beautiful string google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); from coming on user's browser What should i do? I tried using functions to call another page like request dispatcher(), redirect() calling myhtml.js page directly after myservlet process the query results. But i get the result like this google.visualization.Query.setResponse......... /Tiger'},{v:80.0}, {v:false}]}]}}); and the entire myhtml.js code page below it on the browsers that to without the chart been draw. Is there anyway to element the beautiful string from coming on clients browser and only show them the chart been drawn ? :) This is the small tutorial i am following http://code.google.com/apis/visualization/documentation/dev/dsl_get_started.html

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• Java program will read from database, but not write to it

  - by ck1221

  I have a Java program that successfully connects to a mysql database that is hosted on godaddy's server. I can read from that db with out issue, however, when I try to write to it with INSERT or UPDATE for example, the query does not execute. I am using the 'admin' account that I set up through godaddy, I realize this is not the root account. I have checked and verified that the connection is not read only, and have logged out of phpmyadmin while the query ran. I'm not sure what else I can try or if anyone has experienced this issue. Maybe a setting to the connection I have failed to set? Or maybe its not possible since the db is hosted on godaddy's servers? Any help is great! Thanks. Here is some relevant code: Connection to db: Connection con; public DBconnection(String url, String user, String pass) { try { Class.forName("com.mysql.jdbc.Driver").newInstance(); con = DriverManager.getConnection (url,user,pass); if(!con.isClosed()) System.out.println("connecton open"); } catch (InstantiationException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();} catch (SQLException e) {e.printStackTrace();} } Send Query: public ResultSet executeQuery(String query) { ResultSet rs = null; try { Statement stmt = (Statement) con.createStatement(); rs = stmt.executeQuery(query); //while(rs.next()) //System.out.println(rs.getString("ticket_num")); } catch (SQLException e) {} return rs; } Insert Query (works in phpmyadmin): conn.executeQuery("INSERT INTO tickets VALUES(55555,'12/01/2012','me','reports','test','','','0','Nope')");

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• Asus Z8NA-D6, not powering up/no signal for monitor

  - by s093294

  I have a Asus Z8NA-D6 motherboard. Been running fine so far with one E5504 Xeon processor. I have added another Xeon E5504 CPU to the second slot and it will not power up (or there is no signal to the monitor). The status lights turn on as normal. no error led. Nothing happens other then the leds start and both cpus/fans power up. HDD power up. I tried clearing CMOS. Any sugestions? http://www.asus.com/Server_Workstation/Server_Motherboards/Z8NAD6/#download Update. Removing ram for second cpu makes it boot atleast. itboots with memory pluged in for cpu 1. (2 4gb modules) when addin one more to the second cpu it still boots but bios only see the 2 blocks at cpu 1)

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• Viewsonic monitor keeps showing its on-screen menu incessantly

  - by markvgti

  Since yesterday my Viewsonic 22" monitor (VX2255wmb) keeps showing its on-screen menu incessantly, without my touching any of its buttons. The menu comes on in the centre of the screen, stays on for 8-10 seconds, disappears for a second or two, then repeats the cycle. This happens whenever there's a signal being sent to the monitor. I can't actually navigate the menu when it appears on-screen. Pressing the power button, or the Up and Down buttons on its right edge dismiss the menu, only for it to reappear again. These symptoms have appeared before, but earlier they'd stop after 5-10 mins. The power button on the monitor has always been iffy, but now it doesn't seem to be working at all--have to switch off power supply from mains when I leave my desk. Using DVI input on this monitor as my HP desktop has DVI output.

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• vmware takes too much time to shut down

  - by user33754

  Each time I shuting down my virtual machine - it takes like 30 minutes for VM Ware to complete the process. The shut down is done, but it shows a black screen and doesn't respond to any command. I can't do a Power Power OFF or Power Suspend. When I click it - nothing changes. When trying to close - it says "still busy". This happens only when using a Virtual Machine stored on an external hard drive. When Virtual Machine files are stored on a local drive - everything is OK. Hard drive is working good. Any suggestions how can I investigate the issue?

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• Applying iterative algorithm to a set of rows from database

  - by Corvin

  Hello, this question may seem too basic to some, but please bear with be, it's been a while since I dealt with decent database programming. I have an algorithm that I need to program in PHP/MySQL to work on a website. It performs some computations iteratively on an array of objects (it ranks the objects based on their properties). In each iteration the algorithm runs through all collection a couple of times, accessing various data from different places of the whole collection. The algorithm needs several hundred iterations to complete. The array comes from a database. The straightforward solution that I see is to take the results of a database query and create an object for each row of the query, put the objects to an array and pass the array to my algorithm. However, I'm concerned with efficacy of such solution when I have to work with an array of several thousand of items because what I do is essentially mirror the results of a query to memory. On the other hand, making database query a couple of times on each iteration of the algorithm also seems wrong. So, my question is - what is the correct architectural solution for a problem like this? Is it OK to mirror the query results to memory? If not, which is the best way to work with query results in such an algorithm? Thanks!

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• Efficient way to call .Sum() on multiple properties

  - by SherCoder

  I have a function that uses Linq to get data from the database and then I call that function in another function to sum all the individual properties using .Sum on each individual property. I was wondering if there is an efficient way to sum all the properties at once rather than calling .Sum() on each individual property. I think the way I am doing as of right now, is very slow (although untested). public OminitureStats GetAvgOmnitureData(int? fnsId, int dateRange) { IQueryable<OminitureStats> query = GetOmnitureDataAsQueryable(fnsId, dateRange); int pageViews = query.Sum(q => q.PageViews); int monthlyUniqueVisitors = query.Sum(q => q.MonthlyUniqueVisitors); int visits = query.Sum(q => q.Visits); double pagesPerVisit = (double)query.Sum(q => q.PagesPerVisit); double bounceRate = (double)query.Sum(q => q.BounceRate); return new OminitureStats(pageViews, monthlyUniqueVisitors, visits, bounceRate, pagesPerVisit); }

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• Composable FLinq expressions

  - by Daniel

  When doing linq-to-sql in c#, you could do something like this: var data = context.MyTable.Where(x => x.Parameter > 10); var q1 = data.Take(10); var q2 = data.Take(3); q1.ToArray(); q2.ToArray(); This would generate 2 separate SQL queries, one with TOP 10, and the other with TOP 3. In playing around with Flinq, I see that: let data = query <@ seq { for i in context.MyTable do if x.Parameter > 10 then yield i } @> data |> Seq.take 10 |> Seq.toList data |> Seq.take 3 |> Seq.toList is not doing the same thing. Here it seems to do one full query, and then do the "take" calls on the client side. An alternative that I see used is: let q1 = query <@ for i in context.MyTable do if x.Param > 10 then yield i } |> Seq.take 10 @> let q2 = query <@ for i in context.MyTable do if x.Param > 10 then yield i } |> Seq.take 3 @> These 2 generate the SQL with the appropriate TOP N filter. My problem with this is that it doesn't seem composable. I'm basically having to duplicate the "where" clause, and potentially would have to duplicate other other subqueries that I might want to run on a base query. Is there a way to have F# give me something more composable? (I originally posted this question to hubfs, where I have gotten a few answers, dealing with the fact that C# performs the query transformation "at the end", i.e. when the data is needed, where F# is doing that transformation eagerly.)

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