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• Algorithm for creating a school timetable.

  - by cand

  Hello all. I've been wondering if there are known solutions for algorithm of creating a school timetable. Basically, it's about optimizing "hour-dispersion" (both in teachers and classes case) for given class-subject-teacher associations. We can assume that we have sets of classes, lesson subjects and teachers associated with each other at the input and that timetable should fit between 8AM and 4PM. I guess that there is probably no accurate algorithm for that, but maybe someone knows a good approximation or hints for developing it. P.S. I know, there was http://stackoverflow.com/questions/1259686/school-timetable-generation-algorithm-closed , but unlike in that case, I'm not looking for actual implementation, rather for thoughts on how to do it or why it's impossible.

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• Index was outside the bounds of the array. IndexOutOfRangeException in LINQ to SQL

  - by gtas

  Im getting this exception in the protected virtual void SendPropertyChanged(String propertyName) { if ((this.PropertyChanged != null)) { this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); <---- HERE !!! } } of one recently table association i created, there lots of same associations around the database, and this happened in the 4 specific tables i added. Its 1...* relationship and association is Primary Table - Id (identity auto generated) Foreign PId column int not null. I just dont get it....Im using SqlMetal for generation, i regenerated the schema, rebuild, same. This is causing while inserting row in DevExpress XtraGrid, but i dont think this should be issue, same control with same functionality but for different tables works ok. I use grid's event for append value in a property when the entity creating. I disabled this but same again. Recreated the association. No change, exception occurs. Any ideas?

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• Datamapper has n relationship with multiple keys

  - by jing

  I am working on a simple relationship with DataMapper, a ruby webapp to track games. A game belongs_to 4 players, and each player can have many games. When I call player.games.size, I seem to be getting back a result of 0, for players that I know have games associated with them. I am currently able to pull the player associations off of game, but can't figure out why player.games is empty. Do I need to define a parent_key on the has n association, or is there something else I'm missing? class Game belongs_to :t1_p1, :class_name => 'Player', :child_key => [:player1_id] belongs_to :t1_p2, :class_name => 'Player', :child_key => [:player2_id] belongs_to :t2_p1, :class_name => 'Player', :child_key => [:player3_id] belongs_to :t2_p2, :class_name => 'Player', :child_key => [:player4_id] ... end class Player has n, :games ... end

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• How do I create a check constraint?

  - by Zack Peterson

  Please imagine this small database... Diagram Tables Volunteer Event Shift EventVolunteer ========= ===== ===== ============== Id Id Id EventId Name Name EventId VolunteerId Email Location VolunteerId Phone Day Description Comment Description Start End Associations Volunteers may sign up for multiple events. Events may be staffed by multiple volunteers. An event may have multiple shifts. A shift belongs to only a single event. A shift may be staffed by only a single volunteer. A volunteer may staff multiple shifts. Check Constraints Can I create a check constraint to enforce that no shift is staffed by a volunteer that's not signed up for that shift's event? Can I create a check constraint to enforce that two overlapping shifts are never staffed by the same volunteer?

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• ASP.net MVC - OneToOne relationship with pluralized nomenclature

  - by ludicco

  Hi, I have an OneToOne relationship between my models Account and Company the table names are Accounts and Companies respectively. Here is a brief screenshot of the structure: http://cl.ly/1AEU Everything works well, but mysteriously when I use the OneToOne associations I have accessors like: var db = new DB(); var account = db.Accounts.First(); var company = account.Companies; // note the plural not the singular accessor So, what's happing is that even if using OneToOne association, I still get the plural accessor with "companies" and not "company", if it this is a pure object representation and not an EntitySet generated in case when it s an oneToMany relationship. Is there a way to get this nomenclature to be applied properly? Thanks a lot

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• Will this safely delete my record?

  - by Sergio Tapia

  I hate these three tables that. Two tables have a many to many relationship and as such it generates a third table. I'm using Linq-to-SQL and in the .dbml file I've dragged all the folder there to the graphic surface. Here is the method I'm using to delete an Area safely. Remember that documents are associated to an Area, so I can't just delete it and leave documents hanging. ScansDataContext db = new ScansDataContext(); /// <summary> /// Deletes an Area object from the database along with all associations in the database. /// </summary> /// <param name="area">Area object to save</param> public void Delete(Area area) { db.DocumentAreaRelations.DeleteAllOnSubmit(area.DocumentAreaRelations); db.Areas.DeleteOnSubmit(area); db.SubmitChanges(System.Data.Linq.ConflictMode.FailOnFirstConflict); }

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• Best practices for using memcached in Rails?

  - by Matt

  Hello everybody, as database transcations in our app are getting more and more time consuming, we have started to use memcached to reduce the amount of queries passed to MySQL. All in all, it works fine and really saves a lot of time. But as caching was "silently appearing" as a workaround to give the app more juice, a lot of our models now contain code like this: def self.all_cached Rails.cache.fetch('object_name') { find( :all, :include => [associations]) } end This is getting more and more a pain as filling and flushing the cache happens in several classes accross the application. Now, I was wondering if there was a better way to abstract memcached logic to make it more powerful and easy to use across all needed models? I was thinking about having some kind of memcached-module which is included in all needed modules. But before playing around, I thought: Let's ask experts first :-) Thanks Matt

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• Action Controller: Exception - ID not found

  - by Danny McClelland

  Hi Everyone, I am slowly getting the hang of Rails and thanks to a few people I now have a basic grasp of the database relations and associations etc. You can see my previous questions here: http://stackoverflow.com/questions/2714621/rails-database-relationships I have setup my applications models with all of the necessary has_one and has_many :through etc. but when I go to add a kase and choose from a company from the drop down list - it doesnt seem to be assigning the company ID to the kase. You can see a video of the the application and error here: http://screenr.com/BHC You can see a full breakdown of the application and relevant source code at the Git repo here: http://github.com/dannyweb/surveycontrol If anyone could shed some light on my mistake I would be appreciate it very much! Thanks, Danny

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• Rails - Override primary key on has_one

  - by Ben Hall

  I have the following associations, basically I want to link via userid and not the id of the object. class Tweet < ActiveRecord::Base has_one :user_profile, :primary_key = 'userid', :foreign_key = 'twitter_userid' class UserProfile < ActiveRecord::Base belongs_to :tweet, :foreign_key = 'userid' However the following spec fails as twitter_userid is reset to the id of the object it "should have the user's twitter id set on their user profile" do t = Tweet.new(:twitter_id = 1, :status = 'Tester', :userid = 'personA', :user_profile = UserProfile.new(:twitter_userid = 'personA', :avatar = 'abc')) t.save! t.user_profile.twitter_userid.should == 'personA' end should have the user's twitter id set on their user profile expected: "personA", got: 216 (using ==) However, the following does pass: it "should return the correct avatar after being saved" do t = Tweet.new(:twitter_id = 1, :status = 'Tester', :userid = 'personA', :user_profile = UserProfile.new(:twitter_userid = 'personA', :avatar = 'abc')) t.save! t.user_profile.avatar.should == 'abc' end How can I force it to use userid and not id? Thanks Ben

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• rails 3.0.3 - ActiveRecord::Relation, undefined method error

  - by brg

  I am having this unexplained ActiveRecord::Relation, undefined method error . I don't know why, since my model association are well defined and the event table has the foreign keys for the user table. I tried using this fix but it failed: Rails 3 ActiveRecord::Relation random associations behavior event.rb class Event < ActiveRecord::Base belongs_to :user attr_accessible :event_name, :Starts_at, :finish, :tracks end user.rb class User < ActiveRecord::Base has_many :events, :dependent = :destroy attr_accessible :name, :event_attributes accepts_nested_attributes_for :events, :allow_destroy = true end schema.rb ActiveRecord::Schema.define(:version = 20101201180355) do create_table "events", :force = true do |t| t.string "event_name" t.string "tracks" t.datetime "starts_at" t.datetime "finish" t.datetime "created_at" t.datetime "updated_at" t.integer "user_id" end end error message NoMethodError in Users#index undefined method `events' for # Extracted source (around line #10): 7: <%= sortable "Tracks" % 8: 10: <% @users.events.each do |event| % 11: <% debugger % 12: 13: <%= event.starts_at % Trace of template inclusion: app/views/users/index.html.erb Rails.root: C:/rails_project1/events_manager Application Trace | Framework Trace | Full Trace app/views/users/_event_user.html.erb:10:in _app_views_users__event_user_html_erb__412443848_34308540_1390678' app/views/users/index.html.erb:7:in_app_views_users_index_html_erb___603337143_34316016_0'

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• NHibernate cascade and inverse

  - by Kordonme

  I have three mappings as follows: public MainChapterMap() { // other properties HasMany(x => x.ClientSpecific).KeyColumn("MainChapterId"); } public MainChapterClientMap() { // other properties References(x => x.MainChapter).Column("MainChapterId"); HasMany(x => x.Details).KeyColumn("MainChapterClientId"); } public MainChapterClientDetailMap() { // other properties References(x => x.MainChapterClient).Column("MainChapterClientId"); } MainChapter has many client-specific chapters. The client-specific chapters (MainChapterClient) has many translations (MainChapterClientDetail) The dele rules should be as follow: When deleting a MainChapter Delete the MainChapterClient row Delete the MainChapterClientDetail row(s) When deleting a MainChapterClient Do NOT delete the MainChapter row Delete the MainChapterClientDetail row(s) When deleting a MainChapterClientDetail Do NOT delete the MainChapter row Do NOT delete the MainChapterClientDetail row(s) But I no matter what I end up getting this error: deleted object would be re-saved by cascade (remove deleted object from associations)[Entities.MainChapterClient#39] I'm not sure how to set up my cascades anymore. Any help are more than welcomed!

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• (N)Hibernate: deleting orphaned ternary association rows when either associated row is deleted.

  - by anthony

  I have a ternary association table created using the following mapping: <map name="Associations" table="FooToBar"> <key column="Foo_id"/> <index-many-to-many class="Bar" column="Bar_id"/> <element column="AssociationValue" /> </map> I have 3 tables, Foo, Bar, and FooToBar. When I delete a row from the Foo table, the associated row (or rows) in FooToBar is automatically deleted. This is good. When I delete a row from the Bar table, the associated row (or rows) in FooToBar remain, with a stale reference to a Bar id that no longer exists. This is bad. How can I modify my hbm.xml to remove stale FooToBar rows when deleting from the Bar table?

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• Database error when deleting entry in my rails app.

  - by Danny McClelland

  Hi Everyone...again! I have almost everything in my Rails app working, with the exception of detroying entries. I can destroy entries for companies but not kases and people. The following error show when trying to do so: SQLite3::SQLException: no such column: kases_people.kase_id: SELECT * FROM "kases" INNER JOIN "kases_people" ON "kases".id = "kases_people".kase_id WHERE ("kases_people".person_id = 5 ) I suspect this is an error with the party model for the has_many :through associations that I dont fully understand. You can find an up to date version of the app at www.github.com/dannyweb/surveycontrol Thanks, Danny

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• nHibernate query by example with multiple associated objects

  - by BurnWithLife

  I'm trying to use nhibernate's query by example to build dynamic queries. I'm stuck on how to code for an example object with multiple associations. Here's an example from NHibernate in Action. Its a User object with Items. Example exampleUser = Example.Create(u).IgnoreCase().EnableLike(MatchMode.Anywhere); Example exampleItem = Example.Create(i).IgnoreCase().EnableLike(MatchMode.Anywhere); return GetSession().CreateCriteria(typeof(User)) .Add( exampleUser ) .CreateCriteria("Items") .Add( exampleItem ) .List<User>(); If the User object has let's say a Category object as a property, how could I add that in to the above example? If i put another CreateCriteria at the end it refers to the Items, not the User.

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• Joining a one-to-many association with a many-to-many association in Rails 3

  - by Maz

  Hi all, I have a many-to-many association between a User class and a Table class. Additionally, i have a one-to-many association between the User and the Table (one User ultimately owns the table). I am trying to access all of the tables which the user may access (essintally joining both associations). Additionally, it would be nice to do this this with named_scope (now scope) Here's what I have so far: class User < ActiveRecord::Base acts_as_authentic attr_accessible :email, :password, :password_confirmation has_many :feedbacks has_many :tables has_many :user_table_permissions has_many :editableTables, :class_name => "Table", :through => :user_table_permissions def allTables editableTables.merge(tables) end end Thanks.

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• Design review - do you think I'm doing this the right way? First commercial project for me!

  - by Sergio Tapia

  I'm tasked with designing an application that will allow a person to scan a legal document, save that associated with a Name and save it to a database. Now, inside of the Organization, there are many departments, and each department can have many sub departments. Problem lies in that some larger organizations will have many departments and smallers ones will only have 1 or two. I've though about creating a Department table and a Supdepartment table to create associations, etc. That way it's extensible and users can dynamically create departments to fit my program to their organizational scheme. Am I approaching this the right way? As I said, this is my first commercial application so I want to do it right and set a name for myself for delivering things on time and good code for other to expand upon.

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• keep open windows console after a python syntax error

  - by basweber

  File associations on my machine (winxp home) are such that a python script is directly opened with the python interpreter. If I double click on a python script a console window runs and every thing is fine - as long as there is no syntax error in the script. In that case the console window opens up for a moment but it is closed immediately. Too fast to read the error message. Of course their would be the possibility to manually open a console window and to execute the script by typing python myscript.py but I am sure that there is a more convenient (i.e. "double click based") solution.

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• Is it possible to group validation?

  - by lambdabutz

  I am using a lot of my own validation methods to compare the data from one association to the other. I've noticed that I'm constantly checking that my associations aren't nil before trying to call anything on them, but I am also validating their presence, and so I feel that my nil checks are redundant. Here's an example: class House < ActiveRecord::Base has_one :enterance, :class => Door has_one :exit, :class => Door validates_presence_of :enterance, :exit validate :not_a_fire_hazard def not_a_fire_hazard if enterance && exit && enterance.location != exit.location errors.add_to_base('If there is a fire you will most likely die') return false end end end I feel like I am repeating myself by checking the existence of enterance and exit within my own validation. Is there a more "The Rails Way" to do this?

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• Visual Studio Config File Editor - Not Formatting

  - by Ian

  Hi All, My VS 2008 seems to be acting a bit weird and the solution is eluding me. The problem is that if I open a config file; app.config or web.config, this looks and behaves as a plain text document. I have no formatting, no coloring, no intellisense and no collapsible or expandable regions. I have reset all setting and restored default file associations. If I go into the setting menu, Text Editor, XML, formatting I see an error "An error occurred loading this property page" Has any one seen this before and have you go a solution. Thanks

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• Table-per-type inheritance insert problem

  - by gzak

  I followed this article on making a table-per-type inheritance model for my entities, but I get the following error when I try to add an instance of a subclass to the database. Here is how I create the subtype: var cust = db.Users.CreateObject<Customer>(); // Customer inherits User db.Users.AddObject(cust); db.SaveChanges(); I get the following error when I make that last call: "A value shared across entities or associations is generated in more than one location. Check that mapping does not split an EntityKey to multiple store-generated columns." With the following inner exception: "An item with the same key has already been added." Any ideas on what I could be missing?

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• CakePHP hasAndBelongsToMany (HABTM) Delete Joining Record

  - by Jason McCreary

  I have a HABTM relationship between Users and Locations. Both Models have the appropriate $hasAndBelongsToMany variable set. When I managing User Locations, I want to delete the association between the User and Location, but not the Location. Clearly this Location could belong to other users. I would expect the following code to delete just the join table record provided the HABTM associations, but it deleted both records. $this->Weather->deleteAll(array('Weather.id' => $this->data['weather_ids'], false); However, I am new to CakePHP, so I am sure I am missing something. I have tried setting cascade to false and changing the Model order with User, User-Weather, Weather-User. No luck. Thanks in advance for any help.

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• CakePHP hasOne ineffeciency?

  - by Andre

  I was looking at examples on the CakePHP website, in particular hasOne used in linking models. http://book.cakephp.org/view/78/Associations-Linking-Models-Together My question is this, is CakePHP using two queries to build the array structure of data returned in a model that uses hasOne linkage? Taken from CakePHP: //Sample results from a $this-User-find() call. Array ( [User] => Array ( [id] => 121 [name] => Gwoo the Kungwoo [created] => 2007-05-01 10:31:01 ) [Profile] => Array ( [id] => 12 [user_id] => 121 [skill] => Baking Cakes [created] => 2007-05-01 10:31:01 ) ) Hope this all makes sense.

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• Rails + simple role system through associative table

  - by user202411

  So I have the Ninja model which has many Hovercrafts through ninja_hovercrafts (which stores the ninja_id and the hovercraft_id). It is of my understanding that this kind of arrangement should be set in a way that the associative table stores only enough information to bind two different classes. But I'd like to use the associative table to work as a very streamlined authorization hub on my application. So i'd also like this table to inform my system if this binding makes the ninja the pilot or co-pilot of a given hovercraft, through a "role" field in the table. My questions are: Is this ugly? Is this normal? Are there methods built into rails that would help me to automagically create Ninjas and Hovercrafts associations WITH the role? For exemple, could I have a nested form to create both ninjas and hcs in a way that the role field in ninjas_hovercrafts would be also filled? If managing my application roles this way isn't a good idea, whats the non-resource heavy alternative (my app is being designed trying to avoid scalability problems such as excessive joins, includes, etc) thank you

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• Generating link path with parameters

  - by fl00r

  Hi. I've got model with many associations. User :has_many = :posts, :videos, :images etc I've got helper method, which receives one of this association draw_chart user.videos def draw_chart(assoc) assoc.each do |a| link_to "update", [a.user, a], :method => :put, :remote => true, :confirm => 'orrly?' end end Problem here is to send extra parameters to update action. For example I want to get this url: /users/1/videos/2?status=done but I am confused how to realize this while I am using [a.user, a] instead of user_videos_path(video, :status => 'done'). But I can't use last, because it can be either videos, or images or anything else

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• Find by include nil object error in rails

  - by SpyrosP

  I've been trying hard to solve this problem but i really don't know what is happening. I have this small piece of code : DiscoveredLocation.find_by_user_id(user.id, :include => [:boss_kills]) The models are : DiscoveredLocation(id, user_id, boss_location_id) BossKill(user_id, monster_id) and associations : Monster belongs_to :boss_location Monster has_many :boss_kills BossKill belongs_to :user BossKill belongs_to :monster DiscoveredLocation belongs_to :user DiscoveredLocation belongs_to :boss_location DiscoveredLocation has_many :monsters, :through => :boss_location DiscoveredLocation has_many :boss_kills, :through => :monsters When i executed the find_by i get this error : NoMethodError in BossesController#index You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occurred while evaluating nil.each If i change the include option to any other model, like :monster, it works great. I'm pretty much owned by this problem :P. Maybe somebody can help me ? :)

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