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• Composite Primary and Cardinality

  - by srini.venigalla

  I have some questions on Composite Primary Keys and the cardinality of the columns. I searched the web, but did not find any definitive answer, so I am trying again. The questions are: Context: Large (50M - 500M rows) OLAP Prep tables, not NOSQL, not Columnar. MySQL and DB2 1) Does the order of keys in a PK matter? 2) If the cardinality of the columns varies heavily, which should be used first. For example, if I have CLIENT/CAMPAIGN/PROGRAM where CLIENT is highly cardinal, CAMPAIGN is moderate, PROGRAM is almost like a bitmap index, what order is the best? 3) What order is the best for Join, if there is a Where clause and when there is no Where Clause (for views) Thanks in advance.

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• How do I do multiple has_and_belongs_to_many associations between the same two classes?

  - by Ermin

  I have the following setup: class Publication < ActiveRecord::Base has_and_belongs_to_many :authors, :class_name=>'Person', :join_table => 'authors_publications' has_and_belongs_to_many :editors, :class_name=>'Person', :join_table => 'editors_publications' end class Person < ActiveRecord::Base has_and_belongs_to_many :publications end With this setup I can do stuff like Publication.first.authors. But if I want to list all publications in which a person is involved Person.first.publications, an error about a missing join table people_publications it thrown. How could I fix that? Should I maybe switch to separate models for authors and editors? It would however introduce some redundancy to the database, since a person can be an author of one publication and an editor of another.

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• Rails 3: habtm migration, primary key issue

  - by Brian Wigginton

  I'm trying to setup a migration file for a habtm relationship, however when I run the migration I'm getting the following error: Primary key is not allowed in a has_and_belongs_to_many join table (parts_vehicles). Here is my migration file (20110111035950_create_parts_vehicles.rb): class CreatePartsVehiclesJoinTable < ActiveRecord::Migration def self.up create_table :parts_vehicles, :id => false do |t| t.integer :part_id t.integer :vehicle_id end end def self.down drop_table :parts_vehicles end end The documentation example states to use :id => false to disable a primary key from being generated, but I'm still getting the error.

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• Cleanest/One-liner way to require all files in directory in Ruby?

  - by viatropos

  When creating gems, I often have a directory structure like this: |--lib |-- helpers.rb `-- helpers |-- helper_a.rb `-- helper_b.rb Inside the helpers.rb, I'm just require-ing the files in the helpers directory. But I have to do things like this: $:.push(File.dirname(__FILE__) + '/helpers') require 'helper_a' require 'helper_b' Is there a way to make that one line so I never have to add to it? I just came up with this real quick: dir = File.join(File.dirname(__FILE__), "helpers") Dir.entries(dir)[2..-1].each { |file| require "#{dir}/#{file[0..-4]}" } But it's two lines and ugly. What's a slick one liner to solve this problem?

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• Gluing tiles together using imagemagick's montage command

  - by AP257

  This seems like it might be a reasonably common question, so I'm going to ask it using as many keywords as I can think of! I have a bunch of (well, nine) tile jpegs, with standard tile filenames. Each jpeg is 220x175 pixels: (top row) tile_1_0_0.jpg tile_1_1_0.jpg tile_1_2_0.jpg (middle row) tile_1_0_1.jpg tile_1_1_1.jpg tile_1_2_1.jpg (bottom row) tile_1_0_2.jpg tile_1_1_2.jpg tile_1_2_2.jpg How can I use imagemagick/montage to 'glue' or join them all together to make a single, coherent image? I don't want to resize them at all, so I guess the final image should be 660x525. That would be montage with no framing, shadowing, bordering, etc - just the nine original images, glued together to make a single jpeg. I know it should be something along these lines, but I'm struggling with getting the order and sizing right: montage +frame +shadow +label -tile 3x3 -geometry <options> *.jpg joined.jpg

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• How to retrieve row count of one-to-many relation while also include original entity?

  - by kaa

  Say I have two entities Foo and Bar where Foo has-many Bar's, class Foo { int ImportantNumber { get; set; } IEnumerable<Bar> Bars { get; set; } } class FooDTO { Foo Foo { get; set; } int BarCount { get; set; } } How can I efficiently sum up the number of Bars per Foo in a DTO using a single query, preferrably only with the Criteria interface. I have tried any number of ways to get the original entity out of a query with ´SetProjection´ but no luck. The current theory is to do something like SELECT Foo.*, BarCounts.counts FROM Foo LEFT JOIN ( SELECT fooId, COUNT(*) as counts FROM Bar GROUP BY fooId ) AS BarCounts ON Foo.id=BarCounts.fooId but with Criterias, and I just can't seem to figure out how.

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• Combine SQL statement

  - by ninumedia

  I have 3 tables (follows, postings, users) follows has 2 fields - profile_id , following_id postings has 3 fields - post_id, profile_id, content users has 3 fields - profile_id, first_name, last_name I have a follows.profile_id value of 1 that I want to match against. When I run the SQL statement below I get the 1st step in obtaining the correct data. However, I now want to match the postings.profile_id of this resulting set against the users table so each of the names (first and last name) are displayed as well for all the listed postings. Thank you for your help! :) Ex: SELECT * FROM follows JOIN postings ON follows.following_id = postings.profile_id WHERE follows.profile_id = 1

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• Reducing a normalized table to one value

  - by Dio

  Hello, I'm sure this has been asked but I'm not quite sure how to properly search for this question, my apologies. I have two tables, Foo and Bar. For has one row per Food, bar has many rows per food matching descriptors. Foo name id Apple 1 Orange 2 Bar id description 1 Tasty 1 Ripe 2 Sweet etc (sorry for the somewhat contrived example). I'm trying to return a query where if, for each row in Foo, Bar contains a descriptor in ('Tasty', 'Juicy') return true ex: Output Apple True Orange False I had been solving this somewhat trivially with a case when I only had one item to match select Foo.name, case bar.description when 'Tasty' then True else 'False' end from Foo left join Bar on foo.id = bar.id where bar.description = 'Tasty' But with multiple items, I keep ending up with extra rows: Output Apple True Apple False etc etc Can someone point me in the right direction on how to think about this problem or what I should be doing? Thank you.

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• Help needed in AdventureWorks in a sql query.

  - by vaibhav

  I was just playing with adventureworks database in sqlserver. I got stuck in a query. I wanted to Select all titles from HumanResources.Employee which are either 'Male' or 'Female' but not both. i.e if title Accountant is Male and Female both I want to leave that title. I need only those titles where Gender is either Male or Female. I have done this till yet. select distinct(title) from humanresources.employee where gender='M' select distinct(title) from humanresources.employee where gender='F' Probably a join between these two queries, would work. But If you have any other solution, please let me know. It is not a homework. :) Thanks in advance.

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• How to use your computer to save the world?

  - by Francisco Garcia

  Sometimes I miss the "help other people" factor within computer-related fields. However, there are little things that we all can do to make this a better place—beyond trying to eradicate annoying stuff such as Visual Basic. You could join a cloud computing network such as World Community Grid to fight cancer, write a charityware application such as Vim, improve office IT infrastructure to support telecommuting and reduce CO2 emissions, use an ebook reader to save paper, ... What else can we do to help others? Which projects can have the biggest impact?

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• Do I need to include all fields in my entity framework model

  - by Jim B

  Quick question for everyone: Do I need to include all the database table fields on my EF model? For example; I've created a sub-model that only deals with tblPayment and associated tables. Now, I need to write a LINQ query to get some information about items. I would typically get this by joining tblPayment to tblInvoice to tblInvoiceItem to finally tblOrderItem. I'm wondering if when I add in those other tables, do I need to include all the fields for tblInvoice and tblInvoiceItem? Ideally; I'd just like to keep the fields I'd need to join on, as that would limit the possibility of my sub-model breaking if other fields on those tables are modified/deleted. Can I do this?

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• Convert SQL to LINQ to SQL

  - by Adam

  Hi I have the SQL query with c as ( select categoryId,parentId, name,0 as [level] from task_Category b where b.parentId is null union all select b.categoryId,b.parentId,b.name,[level] + 1 from task_Category b join c on b.parentId = c.categoryId) select name,[level],categoryId,parentId as item from c and I want to convert it to LINQ to SQL, yet my LINQ skills are not there yet. Could someone please help me convert this. It's the with and union statements that are making this a bit more complex for me. Any help appreciated.

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• Rails Association issue with NoMethodError in event_controller

  - by pmanning

  Kinda a noob trying to understand I think I need to define rsvps but not sure what to put... I'm trying to add a Join/Unjoin button to user created Events, similar to a Follow/Unfollow button for Users. NoMethodError in Events#show undefined method `model_name' for NilClass:Class in line #1 _unjoin.html.erb 1: <%= form_for(current_user.rsvps.find_by_joined_id(@event), 2: html: { method: :delete }) do |f| %> 3: <%= f.submit "Leave", class: "btn btn-large" %> 4: <% end %> events_controller.rb def show @event = Event.find(params[:id]) @user = current_user end Here's the models rsvp.rb class Rsvp < ActiveRecord::Base attr_accessible :joined_id belongs_to :joiner, class_name: "User" belongs_to :joined, class_name: "User" validates :joiner_id, presence: true validates :joined_id, presence: true end user.rb has_many :rsvps, foreign_key: "joiner_id", dependent: :destroy has_many :joined_events, through: :rsvps, source: :joined has_many :reverse_rsvps, foreign_key: "joined_id", class_name: "Rsvp", dependent: :destroy has_many :joiners, through: :reverse_rsvps, source: :joiner event.rb belongs_to :user has_many :rsvps, foreign_key: "joiner_id", dependent: :destroy has_many :joined_events, through: :rsvps, source: :joined has_many :reverse_rsvps, foreign_key: "joined_id", class_name: "Rsvp", dependent: :destroy has_many :joiners, through: :reverse_rsvps, source: :joiner

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• Alternative to 'where col in (list)' for MySQL

  - by user210481

  Hi I have the following table T: id 1 2 3 4 col a b a c I want to do a select that returns the id,col when group by(col) having count(col)1 One way of doing it is SELECT id,col FROM T WHERE col IN (SELECT col FROM T GROUP BY(col) HAVING COUNT(col)>1); The intern select (from the right) returns 'a' and main one (left) will return 1,a and 3,a The problem is that the where in statement seems to be extremely slow. In my real case, the results from the internal select has many 'col's, something about 70000 and it's taking hours. Right now it's much faster to do the internal select and the main select getting all ids and upcs and do the intersection locally. MySQL should be able to handle this kind of query efficiently. Can I substitute the where in for a join or something faster? Thanks

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• How to save the world from your computer?

  - by Francisco Garcia

  Sometimes I miss the "help other people" factor within computer related careers. Sure that out there I could find many great projects improving society, but that is not common. However there are little things that we all can do to make this a better place beyond trying to erradicate annoynig stuff such as Visual Basic. You could join a cloud computing network such as World Community Grid to fight cancer. Write a charityware application such as Vim, improve an office IT infrastructure to support telecommuting and reduce CO2 emissions, use an ebook reader for saving paper... what else would you? which projects do you think can have an impact?

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• Non Technical -Got selected in Well Reputed Organisation but not getting offer letter. What to do..?

  - by Devashri

  Hi, I got selected in a well reputed company on 27th of March for .Net technology and got selection letter. I was told that I will have to join in next 15 days as my notice peroid was 15 days. And I will get my offer letter as I will submit all documents. So I submitted all the documents and I resigned from my curent organisation. But now no communication is being done. I tried to communicate with them but got no respone. Now I resigned from my previous organisation and not getting offer from new one. So what should I do now? I am just waitng for offer letter and looking for another opportunity? Can anyone suggest me the way to get my offer letter..?? I know this question is nontechnical but still I am asking because I would get suggestions or what to do as by IT Professionals who might had gone through the same condition.

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• CakePHP: Using two tables for a single model

  - by mwaterous

  I'm just picking up development in CakePHP right now so forgive me if this seems obvious; it did to me when I first read about has, belongsTo, hasMany, etc. The problem is I would like to associate two tables with a single model, and was wondering if there was a way to configure this so that when CakePHP did it's queries it automatically performed a join on the two tables. I don't want to create a separate model for the second table as it is merely a meta information table - the master table will contain the primary information required, the meta table will be populated with secondary information that is not required and therefore may or may not be set for every row of the master table.

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• Designing a peer to peer network

  - by Varun

  I am designing a simple peer to peer network. The basic architecture will be as follows: A central server- that keeps track of all the peers. The job of this server is to keep track of all the peers that join the network. Every peer could do things: a. Download a file from it's peer b. Push a file (send a file) to it's peer. Could anybody please tell me what would be the best design for such a system? What would be the problems that i might run into and so on. I am planning to use Java as the programming language to implement. Would it be a good choice? Also, is it necessary that i would need a Linux box to develop the system? or is it fine if i use a Windows machine? Your help will be much appreciated! Thanks!

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• Writing a query to find MAX number in PL/SQL

  - by user2461116

  I am suppose to Write a query that will display the largest number of movies rented by one member and that member's name. Give the output column a meaningful name such as MAXIMUM NUMBER. This is what I have. select max(maximum_movies) from (select count(*)maximum_movies from mm_member join mm_rental on mm_rental.member_id = mm_member.member_id group by first, last); I got the maximum number but the output should be like this. First Last Maximum_movies John Doe 4 But the output is Maximum_movies 4 Any suggestions?

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• Deleting an element from an array in perl

  - by Flamewires

  Hey I'm wondering how i can get this code to work, basically i want to keep the lines of $filename as long as they contain the $user in the path. Sry, perl noob. open STDERR, ">/dev/null"; $filename=`find -H /home | grep $file`; @filenames = split(/\n/, $filename); for $i (@filenames) { if ($i =~ m/$user/) { #keep results } else { delete $i; # does not work. } } $filename = join ("\n", @filenames); close STDERR; I know you can delete like delete $array[index] but I don't have an index with this kind of loop that I know of.

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• How to split movie and play parts to look as a whole?

  - by luksow

  I'm writing software which is demonstraiting video on demand service. One of the feature is something similiar to IIS Smooth Streaming - I want to adjust quality to the bandwith of the client. My idea is, to split single movie into many, let's say - 2 seconds parts, in different qualities and then send it to the client and play them. The point is that for example first part can be in very high quality, and second in really poor (if the bandwith seems to be poor). The question is - do you know any software that allows me to cut movies precisly? For example ffmpeg splits movies in a way that join is visible and really annoying (seconds are the measure of precision). I use qt + phonon as a player if it matters. Or maybe you know any better way to provide such feature, without splitting movie into parts?

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• MySQL select two tables at the same time...

  - by Jerry

  Hi all I have two tables and want to make a query. I tried to get team AA and team BB's image base on table A. I used: SELECT tableA.team1, tableA.team2, tableB.team, tableB.image, FROM tableA LEFT JOIN tableB ON tableA.team1=tableB.team The result only display imageA on the column. Are there any ways to select imageA and image B without using the second query? I appreciate any helps! Thanks a lot! My table structure are: table A team1 team2 ------------ AA BB table B team image ------------- AA imagaA BB imageB

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• Rails 4.2: "Assets should not be requested directly without their digests"

  - by Nowaker

  On Rails 4.2.0.beta1 I get an error: Assets should not be requested directly without their digests: Use the helpers in ActionView::Helpers to request fonts/source-sans-pro.woff The stylesheet: @font-face { font-family: 'Source Sans Pro'; font-style: normal; font-weight: 400; src: local('Source Sans Pro'), local('SourceSansPro-Regular'), url(/assets/source-sans-pro.woff) format('woff'); } The configuration is: config.serve_static_assets = true config.assets.js_compressor = :uglifier config.assets.compile = true config.assets.digest = true config.assets.version = '1.0' config.assets.paths << Rails.root.join('app', 'assets', 'fonts') config.assets.precompile += %w(.svg .eot .woff .ttf) Sure I can disable digests and it works again, but I'm interested in using them. Therefore, how do I make use of digests when I need to request source-sans-pro.woff? Please note that I place the fonts in assets/fonts directory, not the public/ directory. I don't see a difference between images and fonts, so I want to keep them under the same directory - app/assets.

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• Problem with SQLite executemany

  - by Strider1066

  I can't find my error in the following code. When it is run a type error is given for line: cur.executemany(sql % itr.next()) = 'function takes exactly 2 arguments (1 given), import sqlite3 con = sqlite3.connect('test.sqlite') cur = con.cursor() cur.execute("create table IF NOT EXISTS fred (dat)") def newSave(className, fields, objData): sets = [] itr = iter(objData) if len(fields) == 1: sets.append( ':' + fields[0]) else: for name in fields: sets.append( ':' + name) if len(sets)== 1: colNames = sets[0] else: colNames = ', '.join(sets) sql = " '''insert into %s (%s) values(%%s)'''," % (className, colNames) print itr.next() cur.executemany(sql % itr.next()) con.commit() if __name__=='__main__': newSave('fred', ['dat'], [{'dat':1}, {'dat':2}, { 'dat':3}, {'dat':4}]) I would appreciate your thoughts.

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• Casting to specific class in HQL

  - by bungrudi

  My situation is like this.. (note: for those who work with JBPM might already familiar with following data structures and HB mapping) Class LongInstance extends from VariableInstance, with the mapping for field "value" overridden in LongInstance. The mapping for VariableInstance is here and for LongInstance here. VariableInstance is polymorphically mapped to a collection in TokenVariableMap, the mapping is here. The question: how can I query the polymorphic collection using specific/overridden property of the member class? I'm looking for something like this "... from TokenVariableMaps tvm left join fetch tvm.variableInstances tvi where cast(tvi as LongInstance).value in(:vars)"

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