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• Implementing Transparent Persistence

  - by Jules

  Transparent persistence allows you to use regular objects instead of a database. The objects are automatically read from and written to disk. Examples of such systems are Gemstone and Rucksack (for common lisp). Simplified version of what they do: if you access foo.bar and bar is not in memory, it gets loaded from disk. If you do foo.bar = baz then the foo object gets updated on disk. Most systems also have some form of transactions, and they may have support for sharing objects across programs and even across a network. My question is what are the different techniques for implementing these kind of systems and what are the trade offs between these implementation approaches?

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• How to make schema and code dynamic?

  - by Jonarch

  I want to make my database schema and application code as dynamic as possible to handle "unknown" use cases and changes. Developing in PHP and MySQL. Twice now I have had to change my entire schema including table and column names and this means the developers have to go back to the application code and modify all the SQL queries and table/columns names. So to prevent this I want to if just like we do on pages where we have page content, title bar etc dynamic like a %variable%, can we do it for the schema and maybe even for the php code functions and classes somehow? It takes weeks to re-do all changes like this vs if it is dynamic it can be done in under a day.

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• Help regarding no sql databases like hadoop, hbase etc

  - by user560370

  I am new to the distributed NoSQL databases like Hadoop, Cassandra, etc. I have few questions for which I seek an expert advice: Can you list problems/challenges one will generally face when making a shift from the present conventional database like MySQL to these large cluster-based databases? What are the difficulties, if any, when one needs to adapt to a newer version of these open source projects? Can you list out the things which are generally stored/kept in memcached for fast rendering of the page? How can I understand the source code of open-source projects so that I can build on it and maybe give back to the community? Above questions may sound to be idiotic and basic but please it's a request for the experts to answer the above questions in detailed and to best of their abilities.

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• Most watched videos this week

  - by Jan Hancic

  I have a youtube like web-page where users upload&watch videos. I would like to add a "most watched videos this week" list of videos to my page. But this list should not contain just the videos that ware uploaded in the previous week, but all videos. I'm currently recording views in a column, so I have no information on when a video was watched. So now I'm searching for a solution to how to record this data. The first is the most obvious (and the correct one, as far as I know): have a separate table in which you insert a new line every time you want to record a new view (storing the ID of the video and the timestamp). I'm worried that I would quickly get huge amounts of data in this table, and queries using this table would be extremely slow (we get about 3 million views a month). The second solution isn't as flexible but is more easy on the database. I would add 7 columns to the "videos" table (one for each day of the week): views_monday, views_tuesday , views_wednesday, ... And increment the value in the correct column based on the day it is. And I would reset the current day's column to 0 at midnight. I could then easily get the most watched videos of the week by summing this 7 columns. What do you think, should I bother with the first solution or will the second one suffice for my case? If you have a better solution please share! Oh, I'm using MySQL.

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• DB Architecture : Linking to intersection or to main tables?

  - by Jean-Nicolas

  Hi, I'm creating fantasy football system on my website but i'm very confuse about how I should link some of my table. Tables The main table is Pool which have all the info about the ruling of the fantasy draft. A standard table User, which contains the usual stuff. Intersection table called pools_users which contains id,pool_id,user_id because a user could be in more than one pool, and a pool contains more than 1 user. The problem Table Selections = that's the table that is causing problem. That's the selection that the user choose for his pool. This is related to the Player table but thats not relevant for this problem. Should I link this table to the table Pools_users or should I link it with both main table Pool and User. This table contains id,pool_id,user_id,player_id,... What is the best way link my tables? When I want to retrieve my data, I normally want the information to be divided BY users. "This user have those selections, this one those selections, etc).

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• 600 tables in DDBB

  - by Michael

  Hi all, I'm a very young software architect. Now I'm working in a very large and I have to lead a group of developers to rewrite all the mortgage system of the bank. I'm looking at database tables and I realize that there is no any data model, neither documentation. The worst part is that there are about 1000 tables in dev environment, and like 600 in production. I trust more the production environment, but anyway, what can I do? I mean, I can suicide me or something, but is there any good reverse engineering tool, so at least I could get the schema definition with the relations between tables and comments extracted from the fields? Can you advice me something? Thanks in advance.

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• Stored Procedure or calculations via IQueryable?

  - by Shawn Mclean

  This is a question that is based on choosing performance over design practices. If I have a method that will be executed many times a second; public static IQueryable<IPerson> InRadius(this IQueryable<IPerson> query, Coordinate center, double radius) { return (from u in query where CallHeavyMathFormula(u, center, radius) select u); } This extension method for IQueryable generates a SQL that does some heavy maths calculation (Cosine, Sine, etc). This would mean the application sends 1-2KB of sql to the server per call. I've heard of placing all application logic, in your application. I also would like to change to a database such as azure or one of those scalable databases in the future. How do I handle something like this? Should I leave it as it is now or write stored procedures? How do applications like twitter or facebook do it?

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• How to Populate ComboBox from access db in C#

  - by Bomboe Cristian

  I have the next combobox: this.comboBoxProd.Enabled = false; this.comboBoxProd.FormattingEnabled = true; this.comboBoxProd.Items.AddRange(new object[] { "Cameras", "------------", " Digital IXUS 850 IS ", " Digital IXUS 900 Ti ", " Digital IXUS 75 -NEW- ", " Digital IXUS 70 -NEW- ", etc. I want to change it and take the values from a db. My database name is bd1.mdb and in the table Cameras it has the following fields: CamID, Cameras, Warranty, Year. I am only interested in the "Cameras" field. Thank you!

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• user height and weight in sql

  - by Samuel

  We are planning to capture a user's height and weight and am looking for ideas on representing them in sql. I have the following questions in mind weight can be expressed in kilograms and grams and height in meters and centimeters, so should I capture them as a BigDecimal with an appropriate precision and scale or capture them as vanilla strings and do the manipulation in the user interface. Note: I am planning to capture the kilograms and grams separately in the user interface. should the metric of measurement be part of the sql (i.e. the end user might want to view this information in pounds, inches according to his preference) OR Should I just support kilograms / meters in the database and do the conversion while showing this in the user interface

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• How to handle Foreign key for optional field in .NET

  - by brz dot net

  What is the best way to handle following situation? A dropdown(for master table) is optional in a particular form. But, In database table the field is constrained with foreign key. If user don't select from dropdown then It creates problem because of foreign key. One solution is to create default option in master table and use it in case of blank selection. but in dropdown, we need to handle this to show on top. Is it perfect solution? Is there any other optimized solution for this? Thanks

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• Python: Time a code segment for testing performance (with timeit)

  - by Mestika

  Hi, I've a python script which works just as it should but I need to write the time for the execution. I've gooled that I should use timeit but I can't seem to get it to work. My Python script looks like this: import sys import getopt import timeit import random import os import re import ibm_db import time from string import maketrans myfile = open("results_update.txt", "a") for r in range(100): rannumber = random.randint(0, 100) update = "update TABLE set val = %i where MyCount >= '2010' and MyCount < '2012' and number = '250'" % rannumber #print rannumber conn = ibm_db.pconnect("dsn=myDB","usrname","secretPWD") for r in range(5): print "Run %s\n" % r ibm_db.execute(query_stmt) query_stmt = ibm_db.prepare(conn, update) myfile.close() ibm_db.close(conn) What I need it the time it takes the execution of the query and written to the file "results_update.txt". The purpose is to test an update statement for my database with different indexes and tuning mechanisms. Sincerely Mestika

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• How to merge existing row with new data in SQLite?

  - by CSharperWithJava

  I have a database full of simple note data, with columns for title, due date, priority, and details. There is also a _id column PRIMARY KEY int. Say I have a note in the table already with some data filled and the rest null. I also have a set of data that will fill all those fields. Is there a way that I can only write data to the fields that are NULL? I can't overwrite existing data, but I'd like to add data to NULL columns. I know the rowId of the target row. If my target row had rowId of 5, I could do something like this: UPDATE SET duedate='some date', priority='2', details='some text' WHERE _id=5 But that would overwrite all the data in that row, and I don't want to lose any data that might be there. How can I change this statement to avoid writing to non-null fields?

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• Sql server execute permission; failure to apply permissions

  - by WestDiscGolf

  I've just migrated from SQL2000 to SQL2008 and I have started getting an execute permission issue on a stored proc which uses sp_OACreate. The rest of the system works fine with the db login which has been setup and added to the database. I've tried: USE master GO GRANT EXEC ON sp_OACreate TO [dbuser] GO But this fails with the following error: Msg 15151, Level 16, State 1, Line 1 Cannot find the user 'dbuser', because it does not exist or you do not have permission. I'm logged into the server as sa with full permissions. I can execute a similar sql statement and apply the permissions to a server role, however not a login/user. How do I apply the changes to the specific user/login? I can apply the permissions to the public role and it resolves my issue; however this seems to be a security issue to me which I don't really want to apply to the live server.

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• Should I use "id" or "unique username"?

  - by roa3

  I am using PHP, AS3 and mysql. I have a website. A flash(as3) website. The flash website store the members' information in mysql database through php. In "members" table, i have "id" as the primary key and "username" as a unique field. Now my situation is: When flash want to display a member's profile. My questions: Should Flash pass the member "ID" or "username" to php to process the mysql query? Is there any different passing the "id" or "username"? Which one is more secure? Which one you recommend? I would like to optimize my website in terms of security and performance.

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• Efficient update of SQLite table with many records

  - by blackrim

  I am trying to use sqlite (sqlite3) for a project to store hundreds of thousands of records (would like sqlite so users of the program don't have to run a [my]sql server). I have to update hundreds of thousands of records sometimes to enter left right values (they are hierarchical), but have found the standard update table set left_value = 4, right_value = 5 where id = 12340; to be very slow. I have tried surrounding every thousand or so with begin; .... update... update table set left_value = 4, right_value = 5 where id = 12340; update... .... commit; but again, very slow. Odd, because when I populate it with a few hundred thousand (with inserts), it finishes in seconds. I am currently trying to test the speed in python (the slowness is at the command line and python) before I move it to the C++ implementation, but right now this is way to slow and I need to find a new solution unless I am doing something wrong. Thoughts? (would take open source alternative to SQLite that is portable as well)

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• How do I avoid a race condition in my Rails app?

  - by Cathal

  Hi, I have a really simple Rails application that allows users to register their attendance on a set of courses. The ActiveRecord models are as follows: class Course < ActiveRecord::Base has_many :scheduled_runs ... end class ScheduledRun < ActiveRecord::Base belongs_to :course has_many :attendances has_many :attendees, :through => :attendances ... end class Attendance < ActiveRecord::Base belongs_to :user belongs_to :scheduled_run, :counter_cache => true ... end class User < ActiveRecord::Base has_many :attendances has_many :registered_courses, :through => :attendances, :source => :scheduled_run end A ScheduledRun instance has a finite number of places available, and once the limit is reached, no more attendances can be accepted. def full? attendances_count == capacity end attendances_count is a counter cache column holding the number of attendance associations created for a particular ScheduledRun record. My problem is that I don't fully know the correct way to ensure that a race condition doesn't occur when 1 or more people attempt to register for the last available place on a course at the same time. My Attendance controller looks like this: class AttendancesController < ApplicationController before_filter :load_scheduled_run before_filter :load_user, :only => :create def new @user = User.new end def create unless @user.valid? render :action => 'new' end @attendance = @user.attendances.build(:scheduled_run_id => params[:scheduled_run_id]) if @attendance.save flash[:notice] = "Successfully created attendance." redirect_to root_url else render :action => 'new' end end protected def load_scheduled_run @run = ScheduledRun.find(params[:scheduled_run_id]) end def load_user @user = User.create_new_or_load_existing(params[:user]) end end As you can see, it doesn't take into account where the ScheduledRun instance has already reached capacity. Any help on this would be greatly appreciated.

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• mysql_real_escape_string and search data in mySql DB

  - by ryrysz

  I have problem with php function : mysql_real_escape_string My test string: @,&!#$%^*()_+' "\/ I add this data to mySql database, like that (in short): $str = mysql_real_escape_string($str); $sql = "INSERT INTO table(company) VALUES('".$str. "')"; In DB is stored as: @,&!#$%^*()_+\' \"\\/ But problem is with find this data by SELECT statement. I want find, company where name is like ' " My SELECT's: SELECT company FROM table WHERE company LIKE '%\' "%'; SELECT company FROM table WHERE company LIKE '%\\' \\"%'; ; not working. This works: SELECT `company` FROM `table` WHERE `company` LIKE '%\\\' \\\\"%'; and SELECT `company` FROM `table` WHERE `company` LIKE '%\\\\\\\' \\\\\\\"%' But I dont know why this work :(. My questions are: why must add so many slashes ? how I can make correct query in PHP: $query = '\' "'; '%'.mysql_real_escape_string($query).'%' result is : '%\' \"%' '%'.mysql_real_escape_string(mysql_real_escape_string($query)).'%' result is : '%\\\' \\\"%' '%'.mysql_real_escape_string(mysql_real_escape_string(mysql_real_escape_string($query))).'%' result is : '%\\\\\\\' \\\\\\\"%' Only last one works good.

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• Architecture for multiple web apps and databases.

  - by Matt

  We used to have only one web app, but now we are breaking it down into multiple ones. Each one will be packaged as separate product (web app) Some have things in common some do not. It was originally coded with php and using Postgresql 8.4 and CodeIgniter as the framework. I am looking for some good suggestions on how I should set up multiple web apps. They all have their own somewhat unique data. Some data in the databases can be common to some apps but not all. All the apps will be on one server and will have some kind of API to manipulate data. I want it to be structured such that one User account can access any product they purchase. (kinda like google accounts) I do not know if its a good idea to have multiple database, or just to have one big one. eventually we will be using S3 for some videos and other images. Your thoughts and suggestions are much appreciated.

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• Drupal 6: using too many Views module causing site to go down cos of too many mysql connection.

  - by artmania

  Hi friends, I have HostGator Baby Shared Plan . I develop Drupal site on. everything was fine at the beginning, then by the time i go further with development, site started ti work really slow. now it is not working at all. giving my sql errors like TOO many connections, etc... I created so many blocks, pages with View. so it makes my site to so much depend on database. should not I do that? can it be the reason of my site's no working now. appreciate helps!!!!

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• FlockDB - What is it? And best cases for it uses.

  - by Guru

  Just came across FlockDB graph database. Details at github /flockDB. Twitter claims it uses FlockDB for the following: Twitter runs FlockDB on a large cluster of machines. we use it to store social graphs (who follows whom, who blocks whom) and secondary indices at twitter. At first glance, setup and trying it doesn't look straight forward. Have anyone already used it / setup this? If so, please answer the following general queries. What kind of applications is it better suited for? (Twitter claims it is simple and very rough, it remains to see what it meant though) How is FlockDB better than other graph db / noSQL db. Have you setup FlockDB, used it for a application? Early advices any? Note: I am evaluating the FlockDB and other graph databases mainly for learning them. Perhaps, I will build an application for that.

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• UI - How I can make users effectively read what my program says?

  - by Magnetic_dud

  I have a simple form that searches through the 2000+ issues of a 3rd party webcomic. (Easy, it's like xkcd: http://url/number That form is as easy as possible, is like this: What number do you want? User writes a number, clicks ok, and goes on the 3rd party website on a new tab Then, my form asks a question: "Did you find that issue memorable? Enter the name here, and we will add it to the "best issues" in home page" When the user will write the name of the issue, it is added to the database (pending moderation by me) So, I supposed this design is the easiest and convenient that users can find. Unfortunately, NONE of the users (maybe a 2% behaved correctly) will actually read what I asked. Some of the issues are offline, and gives a 404. On that issues users will write in the textbox a completely wrong title, and correctly capitalized! It's like if i would name http://xkcd.com/627/ as "The Great Adventures of Jack Smith" Users are from around all over the country, with different browsers, and have a different cookie. I cannot believe that my users will not read what I ask, it is a WHITE PAGE with a button that disappears when clicked and a textbox.... easier than that??? Maybe i should put a checkbox with "I acknowledge that this form is for submitting memorable issues, not for fun"? Oh, who will read that? Or maybe i could enable the textbox only if the user has effectively clicked the link?

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• Which relational databases exist with a public API for a high level language?

  - by Jens Schauder

  We typically interface with a RDBMS through SQL. I.e. we create a sql string and send it to the server through JDBC or ODBC or something similar. Are there any RDBMS that allow direct interfacing with the database engine through some API in Java, C#, C or similar? I would expect an API that allows constructs like this (in some arbitrary pseudo code): Iterator iter = engine.getIndex("myIndex").getReferencesForValue("23"); for (Reference ref: iter){ Row row = engine.getTable("mytable").getRow(ref); } I guess something like this is hidden somewhere in (and available from) open source databases, but I am looking for something that is officially supported as a public API, so one finds at least a note in the release notes, when it changes. In order to make this a question that actually has a 'best' answer: I prefer languages in the order given above and I will prefer mature APIs over prototypes and research work, although these are welcome as well.

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• SQlite/Firebird: Does any of them support multiple concurrent write access ?

  - by Quandary

  Question: I currently store ASP.net application data in XML files. Now the problem is I have asynchronous operations, which means I ran into the problem of simultanous write access on a XML file... Now, I'm considering moving to an embedded database to solve the issue. I'm currently considering SQlite and embeddable Firebird. I'm not sure however if SQlite or Firebird can handle multiple concurrent write access. And I certainly don't want the same problem again. Anybody knows ? SQlite certainly is better known, but which one is better - SQlite or Firebird ? I tend to say Firebird, but I don't really know. No MS-Access or MS-SQL-express recommodations please, I'm a sane person.

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• How do I get the users location latitude and longitude?

  - by kevin Mendoza

  I need to access the users location in this method contained in the mainViewController -(void)loadAnnotations{ [mapView removeAnnotations:mapView.annotations]; CLLocationCoordinate2D workingCoordinate; workingCoordinate.latitude= //here i need the users latitude workingCoordinate.longitude= //here i need the users longitude NSLog(@" this is %@", workingCoordinate.latitude); iProspectLiteAnnotation *tempMine = [[iProspectLiteAnnotation alloc] initWithCoordinate:workingCoordinate]; [tempMine setTitle:@"Present Location"]; [tempMine setAnnotationType:iProspectLiteAnnotationTypeUser]; [mapView addAnnotation:tempMine]; } however the mainViewController is already set to <fipsideViewControllerDelegate> What should I add to the header file and the implementation file to poll the location Manager for the users current latitude and longitude?

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• Store the day of the week and time

  - by bsiddiqui

  I have a two part question about storing day(s) of the week and time in a database. I'm using Rails 4.0, ruby 2.0.0, and postgres. I have certain events and those events have a schedule. For the event Skydiving for example, for example, I might have Tuesday and Wednesday and 3 pm. 1) Is there a way for me to store the the record for Tuesday and Wednesday in one row or do should I have two records? 2) What is the best way to store the day and time? Is there a way to store day of week and time (not datetime) or should these be separate columns? If they should be separate, how would you store day of week? I was thinking of storing them as integer values (0 for Sunday, 1 for Monday, etc) since that's how wday method for the Time class does it. Any suggestions would be super helpful. Thanks!

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