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  • How do I get save (no exclamation point) semantics in an ActiveRecord transaction?

    - by James A. Rosen
    I have two models: Person and Address which I'd like to create in a transaction. That is, I want to try to create the Person and, if that succeeds, create the related Address. I would like to use save semantics (return true or false) rather than save! semantics (raise an ActiveRecord::StatementInvalid or not). This doesn't work because the user.save doesn't trigger a rollback on the transaction: class Person def save_with_address(address_options = {}) transaction do self.save address = Address.build(address_options) address.person = self address.save end end end (Changing the self.save call to an if self.save block around the rest doesn't help, because the Person save still succeeds even when the Address one fails.) And this doesn't work because it raises the ActiveRecord::StatementInvalid exception out of the transaction block without triggering an ActiveRecord::Rollback: class Person def save_with_address(address_options = {}) transaction do save! address = Address.build(address_options) address.person = self address.save! end end end The Rails documentation specifically warns against catching the ActiveRecord::StatementInvalid inside the transaction block. I guess my first question is: why isn't this transaction block... transacting on both saves?

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  • Systems design question: DB connection management in load-balanced n-tier

    - by aoven
    I'm wondering about the best approach to designing a DB connection manager for a load-balanced n-tier system. Classic n-tier looks like this: Client -> BusinessServer -> DBServer A load-balancing solution as I see it would then look like this: +--> ... +--+ +--> BusinessServer +--+--> SessionServer --+ Client -> Gateway --+--> BusinessServer +--| +--> DBServer +--> BusinessServer +--+--------------------+ +--> ... +--+ As pictured, the business server component is being load-balanced via multiple instances, and a hardware gateway is distributing the load among them. Session server probably needs to be situated outside the load-balancing array, because it manages state, which mustn't be duplicated. Barring any major errors in design so far, what is the best way to implement DB connection management? I've come up with a couple of options, but there may be others I'm not aware of: Introduce a new Broker component between the DBServer and the other components and let it handle the DB connections. The upside is that all the connections can be managed from a single point, which is very convenient. The downside is that now there is an additional "single point of failure" in the system. Other components must go through it for every request that involves DB in some way, which also makes this a bottleneck. Move the DB connection management into BusinessServer and SessionServer components and let each handle its own DB connections. The upside is that there is no additional "single point of failure" or bottleneck components. The downside is that there is also no control over possible conflicts and deadlocks apart from what DBServer itself can provide. What else can be done? FWIW: Technology is .NET, but none of the vendor-specific stacks are used (e.g. no WCF, MSMQ or the like).

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  • Question About DateCreated and DateModified Columns - MS SQL Server

    - by user311509
    CREATE TABLE Customer ( customerID int identity (500,20) CONSTRAINT . . dateCreated datetime DEFAULT GetDate() NOT NULL, dateModified datetime DEFAULT GetDate() NOT NULL ); When i insert a record, dateCreated and dateModified gets set to default date/time. When i update/modify the record, dateModified and dateCreated remains as is? What should i do? Obviously, i need to dateCreated value to remain as was inserted the first time and dateModified keeps changing when a change/modification occurs in the record fields. In other words, can you please write a sample quick trigger? I don't know much yet... Any help will be appreciated.

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  • Updating multiple tables with LinqToSql in one unit of work

    - by zsharp
    Table 1: int ID-a(pk) Table 2: int ID-a(pk), int ID-b(pk) Table 3: int ID-b(pk), string C I have the data to insert into Table 1. But I do not have the ID-a, which is autogenerated. I have many string C to insert in Table 3. I am trying to insert row into Table 1, get the ID-a to insert in Table 2 along with the ID-b that is auto-Generated in Table 3 when I submit each string C, all in one submission to db. Right now I am calling dc.SubmitChanges twice in same call. Is it efficient to have to submit changes twice on same DataContext or can this be combined further?

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  • Comparing COUNT values within a query?

    - by outsyncof
    I have the following tables in a relation: person(ssn,sex) employment(ssn,workweeksperyear) assume ssn is a key. My assignment was to do this: Given as input the number of weeks per year a person has worked, determine whether there are more males than females who work more weeks than the input value. SELECT COUNT(sex) AS NumMales FROM person WHERE sex = 'Male' AND ssn IN (SELECT ssn FROM employment WHERE workweeksperyear > 48); The above query gets me the number of males for an input value and I could do the same for number of females but how do I compare the 2 results? Any help will be greatly appreciated!

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  • Question About DateCreated and DateModified Columns - SQL Server

    - by user311509
    CREATE TABLE Customer ( customerID int identity (500,20) CONSTRAINT . . dateCreated datetime DEFAULT GetDate() NOT NULL, dateModified datetime DEFAULT GetDate() NOT NULL ); When i insert a record, dateCreated and dateModified gets set to default date/time. When i update/modify the record, dateModified and dateCreated remains as is? What should i do? Obviously, i need to dateCreated value to remain as was inserted the first time and dateModified keeps changing when a change/modification occurs in the record fields. In other words, can you please write a sample quick trigger? I don't know much yet...

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  • How do you determine an acceptable response time for DB requests?

    - by qiq
    According to this discussion of Google App Engine on Hacker News, A DB (read) request takes over 100ms on the datastore. That's insane and unusable for about 90% of applications. How do you determine what is an acceptable response time for a DB read request? I have been using App Engine without noticing any issues with DB responsiveness. But, on the other hand, I'm not sure I would even know what to look for in that regard :)

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  • SQL Compact import DB from SQL Server Express with Server Management Studio

    - by Sasha
    Hi! I try to import sql script, generated with Server Management Studio, into SQL Compact 3.5 and get a lot of error. What I am doing wrong? I generate script with "Task/Generate Script" context menu. Part of my script: CREATE TABLE [LogMagazines]( [IdUser] [int] NOT NULL, [Text] [nvarchar](500) NULL, [TypeLog] [int] NOT NULL, [DateAndTime] [datetime] NOT NULL, [DetailMessage] [nvarchar](max) NULL, [Id] [int] IDENTITY(1,1) NOT NULL, CONSTRAINT [PK_LogMagazines] PRIMARY KEY ( [Id] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] Knowledge Base: http://stackoverflow.com/questions/1525063/how-to-import-data-in-sql-compact-edition http://stackoverflow.com/questions/1515969/exporting-data-in-sql-server-as-insert-into/1515975

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  • Which is better practice: complex SQL statements or Recordset manipulation in Access VBA?

    - by mazi
    I'm doing some VBA development and I found creating SQLs quite efficient way of getting everything done (selecting and updating). But I got to this stage where my SQL statements contain complex Switches and WHERE conditions where I have another Selects to update appropriate records. Therefore, I create this SQLs and I simply run it via "CurrentDb.Execute strSQL" and it does everything fine. The question is, why would I declare ADODB.connections etc, set recordsets, loop through it and manipulate the data one by one?

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  • Fastest method for SQL Server inserts, updates, selects from C# ASP.Net 2.0+

    - by Ian
    Hi All, long time listener, first time caller. I use SPs and this isn't an SP vs code-behind "Build your SQL command" question. I'm looking for a high-throughput method for a backend app that handles many small transactions. I use SQLDataReader for most of the returns since forward only works in most cases for me. I've seen it done many ways, and used most of them myself. Methods that define and accept the stored procedure parameters as parameters themselves and build using cmd.Parameters.Add (with or without specifying the DB value type and/or length) Assembling your SP params and their values into an array or hashtable, then passing to a more abstract method that parses the collection and then runs cmd.Parameters.Add Classes that represent tables, initializing the class upon need, setting the public properties that represent the table fields, and calling methods like Save, Load, etc I'm sure there are others I've seen but can't think of at the moment as well. I'm open to all suggestions.

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  • html-encode output && incorrect string error

    - by fusion
    my data includes arabic characters which looks like garbage in mysql but displays correctly when run on browser. my questions: how do i html-encode the output? if i add this to all my files: <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> i get this error: Error: Incorrect string value: '\xE4\xEE\xC3\xD8\xEF\xE6...' for column 'cQuotes' at row 1 i'm working on php/mysql platform. insertion form in html: <!doctype html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Your Favorite Quotes</title> <link rel="stylesheet" type="text/css" href="style.css" /> <link rel="stylesheet" href="css/validationEngine.jquery.css" type="text/css" media="screen" charset="utf-8" /> <script type="text/javascript" src="scripts/jquery-1.4.2.js"></script> <script src="scripts/jquery.validationEngine-en.js" type="text/javascript"></script> <script src="scripts/jquery.validationEngine.js" type="text/javascript"></script> <script type="text/javascript"> $(document).ready(function() { $("#submitForm").validationEngine() }) </script> </head> <body> <div class="container"> <div class="center_div"> <h2>Submit Your Quote</h2> <fieldset> <form id="submitForm" action="qinsert.php" method="post"> <div class="field"> <label>Author: </label> <input id="author" name="author" type="text" class="validate[required,custom[onlyLetter],length[0,100]]"> </div><br /> <div class="field"> <label>Quote: </label> <textarea id="quote" name="quote" class="validate[required, length[0,1000]]"></textarea> <br /> </div> <input id="button1" type="submit" value="Submit" class="submit" /><br /> <input id="button2" type="reset" value="Reset" /> </form> </fieldset> </div> </div> </body> </html> ////////////////////// query in php: //<?php //header('Content-Type: text/html; charset=UTF-8'); //?> <!doctype html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <link rel="stylesheet" type="text/css" href="style2.css" /> <title>Your Quote Databank</title> </head> <body> <?php include 'config.php'; echo "Connected <br />"; //check for quotes and apostrophes $author = ''; $quote = ''; $author = $_POST['author']; $quote = $_POST['quote']; $author = mysql_real_escape_string(trim($author)); $quote = mysql_real_escape_string(trim($quote)); //************************** //validating data $query = "SELECT * FROM Quotes where cQuotes = '$quote' limit 1;"; $result = mysql_query($query, $conn); //now check that the number of rows is 0 if (mysql_num_rows($result) > 0 ) { header("Location: /error.html"); exit; } //inserting data //mysql_query("SET NAMES 'utf8'"); //mysql_query("SET CHARACTER SET utf8"); $sql="INSERT INTO Quotes (vauthor, cquotes) VALUES ('$author', '$quote')"; if (!mysql_query($sql,$conn)) { die('Error: ' . mysql_error()); } echo "<div class='container'><p><label class='lbl_record'> Record Added Successfully!</label>"; echo "<a href='qform.html'> Submit a New Quote!</a></p>"; //************************** //selecting data $result = mysql_query("SELECT * FROM Quotes ORDER BY idQuotes DESC"); echo "<div class='center_div'>"; echo "<table> <thead> <tr> <th>Author</th> <th>Quotes</th> </tr> </thead>"; while($row = mysql_fetch_array($result)) { echo "<tbody><tr>"; echo "<td width='150px'>" . $row['vAuthor'] . "</td>"; echo "<td>" . $row['cQuotes'] . "</td>"; echo "</tr>"; } echo "</tbody></table>"; echo "</div></div>"; //************************** include 'close_config.php'; ?> </body> </html>

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  • Single HTML Table from multiple MySQL tables

    - by David Chouinard
    Hi! I've been struggling for a while with this one; I'll try to explain it here as simply as possible. Consider this MySQL table: +----------+-----------+---------+--------+ |status_id |session_id |pilot_id |present | +----------+-----------+---------+--------+ |1 |61 |901 |1 | |2 |63 |901 |1 | |3 |62 |901 |0 | |4 |62 |902 |1 | |5 |63 |903 |1 | +----------+-----------+---------+--------+ Both session_id and pilot_id are foreign keys making reference to a primary key in another table. The same pilot_id can be associated with different session_id, but every pilot_id-session_id combination is unique. I need to make an HTML table (in PHP) that would display the data like this: +----------+---------+---------+---------+ | |61 |62 |63 | +----------+---------+---------+---------+ |901 |X | |X | |902 | |X | | |903 | | |X | +----------+---------+---------+---------+ Hence, rows are pilot_id and columns are session_id. When a pilot_id-session_id combination has a present value of 1, the corresponding cell should be checked. (ie. when the row-combination is zero or the combination does not exist in the MySQL table, nothing should appear in the HTML table) Phew. Any ideas? Thanks!

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  • Update MySQL table from jsp

    - by vishnu
    I have these in a jsp file. But these values are not updated in the mysql table. May be it is not commiting. How can i solve this ? String passc1 = request.getParameter("passc1"); String accid = request.getParameter("accid"); int i = 0; String sql = " update customertb " + " set passwd = ?" + " where acc_no = ?;"; try { PreparedStatement ps = con.prepareStatement(sql); ps.setString(1, passc1); ps.setString(2, accid); i = ps.executeUpdate(); } catch (Exception e) { // do something with Exception here. Maybe just throw it up again } finally { con.close(); }

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  • MongoDB RSS Feed Entries, Embed the Entries in the Feed Object?

    - by Patrick Klingemann
    I am saving a reference to an RSS Feed in MongoDB, each Feed has an ever growing list of Entries. As I'm designing my schema, I'm concerned about this statement from the MongoDB Schema Design - Embed vs. Reference Documentation: If the amount of data to embed is huge (many megabytes), you may read the limit on size of a single object. This will surely happen if I understand the statement correctly. So the question is, I am correct to assume that I should not embed the Feed Entries within a Feed because I'll eventually reach the limit on size of a single object?

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  • Combining cache methods - memcache/disk based

    - by Industrial
    Hi! Here's the deal. We would have taken the complete static html road to solve performance issues, but since the site will be partially dynamic, this won't work out for us. What we have thought of instead is using memcache + eAccelerator to speed up PHP and take care of caching for the most used data. Here's our two approaches that we have thought of right now: Using memcache on all<< major queries and leaving it alone to do what it does best. Usinc memcache for most commonly retrieved data, and combining with a standard harddrive-stored cache for further usage. The major advantage of only using memcache is of course the performance, but as users increases, the memory usage gets heavy. Combining the two sounds like a more natural approach to us, even though the theoretical compromize in performance. Memcached appears to have some replication features available as well, which may come handy when it's time to increase the nodes. What approach should we use? - Is it stupid to compromize and combine the two methods? Should we insted be focusing on utilizing memcache and instead focusing on upgrading the memory as the load increases with the number of users? Thanks a lot!

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  • SQLAlchemy - relationship limited on more than just the foreign key

    - by Marian
    I have a wiki db layout with Page and Revisions. Each Revision has a page_id referencing the Page, a page relationship to the referenced page; each Page has a all_revisions relationship to all its revisions. So far so common. But I want to implement different epochs for the pages: If a page was deleted and is recreated, the new revisions have a new epoch. To help find the correct revisions, each page has a current_epoch field. Now I want to provide a revisions relation on the page that only contains its revisions, but only those where the epochs match. This is what I've tried: revisions = relationship('Revision', primaryjoin = and_( 'Page.id == Revision.page_id', 'Page.current_epoch == Revision.epoch', ), foreign_keys=['Page.id', 'Page.current_epoch'] ) Full code (you may run that as it is) However this always raises ArgumentError: Could not determine relationship direction for primaryjoin condition ...`, I've tried all I had come to mind, it didn't work. What am I doing wrong? Is this a bad approach for doing this, how could it be done other than with a relationship?

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  • Any difference in performance/compatibility of different languages in PostgreSQL?

    - by Igor
    In nowadays the PostgreSQL offers plenty of procedural languages: pl/pgsql, pl/perl, etc Are there any difference in the speed/memory consumption in procedures written in different languages? Does anybody have done any test? Is it true that to use the native pl/pgsql is the most correct choice? How the procedure written in C++ and compiled into loadable module differs in all parameter w.r.t. the user function written with pl/* languages?

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  • I am not able to drop foreign key in mysql Error 150. Please help

    - by Shantanu Gupta
    i am trying to create a foreign key in my table. But when i executes my query it shows me error 150 Error Code : 1005 Can't create table '.\vts#sql-6ec_1.frm' (errno: 150) (0 ms taken) My Queries are Query to create a foreign Key alter table `vts`.`tblguardian` add constraint `FK_tblguardian` FOREIGN KEY (`GuardianPickPointId`) REFERENCES `tblpickpoint` (`PickPointId`) EDIT: Now I am trying to drop this constraint But it fails again and shows me same error as it was giving when i was trying to create foreign key. alter table `vts`.`tblguardian` drop index `FK_tblguardian` Primary Key table CREATE TABLE `tblpickpoint` ( `PickPointId` int(4) NOT NULL auto_increment, `PickPointName` varchar(500) default NULL, `PickPointLabel` varchar(500) default NULL, `PickPointLatLong` varchar(100) NOT NULL, PRIMARY KEY (`PickPointId`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 CHECKSUM=1 DELAY_KEY_WRITE=1 ROW_FORMAT=DYNAMIC Foreign Key Table CREATE TABLE `tblguardian` ( `GuardianId` int(4) NOT NULL auto_increment, `GuardianName` varchar(500) default NULL, `GuardianAddress` varchar(500) default NULL, `GuardianMobilePrimary` varchar(15) NOT NULL, `GuardianMobileSecondary` varchar(15) default NULL, `GuardianPickPointId` int(4) default NULL, PRIMARY KEY (`GuardianId`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1

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