associations

问题 Is there a way to check if an ActiveRecord's belongs_to association exists without incurring a database query. I'm using example_association.present? to check and it results in the association being loaded if it does. All I want to know is if the association exists. 回答1: You could use reflect_on_all_associations as: Foo.reflect_on_all_associations(:belongs_to).map(&:name).include?(:example_assoc) Where :example_assoc is one of the belongs_to association. Or if you have an instance of model

问题 I am using Ruby on Rails 3.0.7 and I followed this post about handling an " has_many :through => checkboxes " in which, in order to create user-group relationship records for membership purposes, is just passed a group_ids parameter (that is an array of id values) from check box input fields to the @user.save method. Using that code all works good in a "RoR magical\automatic way" (RoR set properly user_id values in the related memberships database table). However, on saving, I would like to

问题 In Rails 4.0 I have 2 ActiveRecord classes: class Sequence < ActiveRecord::Base has_many :steps, dependent: :destroy end and class Steps < ActiveRecord::Base belongs_to :sequence default_scope -> { order('order ASC') } end When I call mySequence.destroy I get this error: PG::SyntaxError: ERROR: syntax error at or near "order" LINE 1: ...steps" WHERE "steps"."sequence_id" = $1 ORDER BY order ASC ^ : SELECT "steps".* FROM "steps" WHERE "steps"."sequence_id" = $1 ORDER BY order ASC When I remove

问题 I have a table(drugs) which lists all of the drugs in that table. Drugs hasOne french_information and french_information belongsTo Drugs. I would like for the users to be able to click a drug,have information about it displayed and then select french and have it bring up a view to add french information,while displaying the chosen drugs information, with fields to add french info for it and store it in the french_information table. How would I do that? 回答1: You wouldn't. There's no need to

问题 I have an object that I am developing a controller for that has many attributes. However, due to the data model I have created, most of the attributes that I have to edit are saved through associations in other tables. EG: I have articles that have tags through a taggings table (and about 20 other attributes saved in other tables). THe article has many other attributes through polymorphic associations etc.. The associations work great, and enable the saving of multiple entries of each

问题 Im trying to add functionality to my Rails 4 app which allows a user (who creates a project) to invite others to join their project team. I found this tutorial, which I've found helpful: https://coderwall.com/p/rqjjca/creating-a-scoped-invitation-system-for-rails To this point, I have the following set up: User has_one :profile, dependent: :destroy Profile belongs_to :user has_many :teams, foreign_key: "team_mate_id" has_many :team_projects, through: :teams, source: :project has_many

问题 I'm wondering why Item.where(category: x) isn't working for me. I expect this statement to return all items which are categorized under category x. Please see below my associations: class Category < ActiveRecord::Base has_many :categorizations has_many :items, :through => :categorizations end class Item < ActiveRecord::Base has_many :categorizations has_many :categories, :through => :categorizations end class Categorization < ActiveRecord::Base belongs_to :item belongs_to :category end

问题 how can I pass constant value '1111' to a nested column with mybatis association? <association property="certificateType" column="{VALUE=CERTIFICATE_TYPE,TYPE='1111'}" select="getDict"/> 回答1: Depending on what your db is, you can use IFNULL(#{TYPE}, '1111') (mysql) ISNULL(#{TYPE}, '1111') (sql server) In your subquery (getDict). Another solution is that your parent query can return TYPE as a value For example by saying: SELECT '1111' AS TYPE, ..... Then in your column you can just say column=

问题 I've got an address form nested into a user form but cant get the foreign key to fill. I've seen people suggest using a hidden field, but that seems to be a bad idea from a security standpoint. How exactly do you set the foreign key using the controller? Right now I'm getting Address user can't be blank error when I try to submit MVC below user\new.html.erb <div> <%= form_for(@user) do |f| %> <%= render 'shared/error_messages' %> <%= f.label :rank %> <%= f.text_field :rank %> <%= f.label

问题 I have a rather complex mostly-python application (that I inherited) and when I run it in windows from a file type association (double click on a data file in explorer), I get a crash in the middle of the python multiprocessing: Traceback (most recent call last): File "<string>", line 1, in <module> File "c:\Python27\lib\multiprocessing\forking.py", line 380, in main prepare(preparation_data) File "c:\Python27\lib\multiprocessing\forking.py", line 489, in prepare file, path_name, etc = imp