associations

问题 Hi, I have recently started to learn system analysis and design and am having some trouble understanding domain model class diagram (DMCD) association class. As per image, when drawing the DMCD, I'd like to understand if an association class is allowed to contain attributes of the classes it derives from. The Invoice needs to contain the attributes apptNo and svcName. Association class inquiry image: Do I include the attributes as shown in the image? Or do I assume that the Invoice would

问题 Generally,the CRUD operation url pattern for model can be like this(Suppose the Model is Post): new: /posts/new(get) create:/posts/(post) edit:/posts/edit(get) update:/posts/1(put) get:/posts/1(get) However if there is a nested model "Comment". And the association of the "Post" and "Comment" is one-many. So what should the CURD operation url pattern like for comments ? new: /posts/1/comments/new or /comments/new create:? edit:? update:? ....... What is the best practice? Update: It seems that

问题 I have the following code (somewhat simplified ... create_table :signatures do |t| t.integer :signer_id t.integer :card_id t.timestamps end With the models looking like ... class Signature < ActiveRecord::Base belongs_to :card belongs_to :user end class Card < ActiveRecord::Base has_many :signatures has_many :signers, :through => :signatures, :foreign_key => "card_id" end class User < ActiveRecord::Base has_many :sent_cards, :class_name => "Card", :foreign_key => "sender_id" has_many

问题 Two database tables have a foreign key relationship. They are mapped to two entities A and B by JPA, but the join columns are manually removed from the entities, so in JPA world classes A and B are not related and you cannot navigate from one to the other through a field/property. Using the JPA Criteria API, is it possible to create a query which joins the two tables? All examples I found on internet uses the join column to achieve the goal, but, as stated above, it was removed from the code

问题 I tried to search other posts in R related to this, but did not find duplicated questions(at least to my efforts). I know I need a priori function in library("a rules") though. I have a large array file A that each row is a list user1: [1,2,3,4] # [1,2,3,4] is the itemList purchased by this user user2: [4] ................ I want to find items that tend to be purchased together. How should I proceed? It seems I need to convert the data to "transaction" format file also. So I did temp <- split

问题 I've been trying, for the last few months, to figure out how to set up an evaluation model so that some users can evaluate other users on their joint projects. I previously asked this question, but have since had some advice that the suggestion to make this model polymorphic was not the right approach. I wasn't actually able to get the advice in this post working, but my question is now slightly different. http://stackoverflow.com/questions/36394489/rails-4-polymorphic-associations-and

问题 So I'm trying to work this out last night, and after thinking myself around in circles a few times decided I need some help. I did post a question about an ID field not being filled in but it got too long winded and confusing, and I realised the problem was probably based on the associations. I'm working on a customer database. For larger business customers the relationships get a little complicated. I have 3 models, Customer, CustomerAddress and CustomerContact. A customer can have many

问题 I have three tables: Member MemberBranch Branch The Member can have many Branch es through MemberBranch . And a Branch can have many Member s etc. What I want to be able to do is get a count of how many members a branch has. so $branch = Branch::find_by_title('London'); $branch->number_of_members; // Will equal how many members have the branch through MemberBranch How would I go about doing this? 回答1: Try this: SELECT B.*, (SELECT count(*) as total from MembersBranch where branch_id = B.id)

问题 If I have 3 models: Model Section Model User has_many :votes Model Vote belongs_to :user and inside Model Section has_many :users has_many :votes, :through => :users How to get the Sections list ordered by votes quantity using the AR associations? 回答1: The most reasonable way to do this is to use a subquery written as raw SQL for ordering the result as follows... Section.order( '(select count(1) from votes inner join users on votes.user_id=users.id where users.section_id=sections.id)' ) 回答2:

问题 An Organization model has a 1:many association with a User model. I have the following validation in my User model file: belongs_to :organization validates_presence_of :organization_id, :unless => 'usertype==1' If usertype is 1, it means the user will have no organization associated to it. For a different usertype the presence of an organization_id should be mandatory. The organization model includes: has_many :users accepts_nested_attributes_for :users, :reject_if => :all_blank, :allow