I'm currently working on a data model design (which will be backed by an RDMS). It is based around 3 entities relating to benefits for a member of the organization. The entities are the Benefit, Membership Type, and Provider. I've created a standard many-to-many intersection table to relate two entities, but never 3. I'm wondering if any...
Hi, I have a situation where I have Products, Suppliers, ShoppingLists and Valuations. A shopping_list consist of many valuations each with a product, an specific supplier and a price. My models are as follows: class Product < ActiveRecord::Base has_many :valuations has_many :shopping_lists, :through => :valuations end class Supp...
Hi All I'm new to nhibernate, and I'm sorry if this is answered elsewhere, but I've been looking for the last couple of hours, and can't find a solution that works. A bit of background: I'm trying to write an Admin area where there are users and sites, and a user can have access to multiple sites - but at various permission levels for ...
In many database design tutorials/articles, they always bring up the fact that if two tables share a many-to-many relationship, then a third table should be created to act as an associate table to link the two. However, they never provide the reason WHY we should do it that way. I'm curious to know why and examples of problems that coul...
Hello all, I have an entity called Strategy, and another one called Team. Both are mapped using a Many-To-Many relationship: public class Team : BaseEntity<Team> { private readonly IList<Strategy> allStrategies = new List<Strategy>(); public void AddStrategy(Strategy strategy) { allStrategies.Add(strategy); ...
If my models.py has a ManyToMany relationship between books and authors, and if for a particular SampleBook I execute: Sample_book.authors.add(author1) Sample_book.authors.add(author2) Sample_book.authors.add(author3) are author1, author2, and author3 stored in books.authors.all in the order in which they were added? i.e. is the ManyTo...
I've created two JPA entities (Client, InstrumentTraded) using Hibernate as a provider that have a ManyToMany relationship. After letting Hibernate generate the tables for MySQL it appears that the ManyToMany relationship table does not contain primary keys for the two foreign keys. This allows duplicate records in the many-to-many tab...
Given the following POCO classes: public class Certification { public int Id { get; set; } public virtual ICollection<Employee> CertifiedEmployees { get; set; } } public class Employee { public int Id { get; set; } public virtual ICollection<Certification> Certifications { get; set; } } Creating the database model usi...
I am getting "During synchronization a new object was found through a relationship that was not marked cascade PERSIST" when attempting to persist an object Word() that has a Many-To-Many field mapping to a table Topics. The relations bridge table is Topic_links. What complicates the problem is that I always use the Eclipse Workbench to...
Say for example I had to entities "Article" and "Tag" (like in a typical blog). Each article can have many tags, and each tag can be used by many articles, so it is a classical m:n relationship. I need to specify an owning side with JPA. But which side should be the owning side? An article doesn't depend on a certain tag and vice versa....
category_product --------------- id_category id_product product --------------- id_product id_manufacturer manufacturer --------------- id_manufacturer name How would I create an SQL query so that it selects all the names from manufacturer when id_category is equal to something? ...
I have a Ruby on Rails application in which the code directly access many-to-many join tables directly. This makes modifying some of the code very difficult since it bypasses the normal associations and methods created via the :has_many and :has_many :through relationships. My question is simply, is this an acceptable thing to be doing ...
If I have two classes A and B with a many to many relationship and I want to delete an instance of A, do I need to remove all of its related Bs first or will Django sort that out for me? I obviously don't want to leave orphaned rows in the join table. Does it make any difference if the ManyToMany field is declared on class A or B? Doe...
Hi all, I have two entities: Student and Course with manytomany relationship. I wanna give a student a list of the courses he did not choose yet. For example, If we have 6 courses, and stduent A has selected course 1 , 3, 5, we should list course 2,4 in the available courses list for him. What's the right JPQL for that? Thanks. ...
I have two tables: - Attendees - Events Normally, I would create a mapping table 'EventAttendeeMap' to link these tables into a many to many relationship. Is this the best way of doing so? Should I store the list of AttendeeIds in an xml column instead on the Events table? I am using .NET 3.5/4 with Linq as the DAL (although I think...
Ok so I have a site with users. I want a user to be able to send a message to multiple users based on a search query. Eg. John searches for "Florida" and this search returns 1 million users/companies. Whats the best way to let john send a message to all those users/companies returned by the search result? Lets say, Susan was 1 of thos...
Consider the following models: class Person(models.Model): name = models.CharField(max_length=128) class Group(models.Model): name = models.CharField(max_length=128) members = models.ManyToManyField(Person, through='Membership') class Membership(models.Model): person = models.ForeignKey(Person) group = models.Forei...
I have a data set of books and authors, with a many-to-many relationship. There are about 10^6 books and 10^5 authors, with an average of 10 authors per book. I need to perform a series of operations on the data set, such as counting the number of books by each author or deleting all books by a certain author from the set. What would ...
In Grails, I like to have a many-to-many relation among entries of the same domain class Person. Relations will link to different persons the "leftPerson" and the "rightPerson" since the "Parent-child" and "Employer-Employee" relations will discriminate the position of each link. That I would like to have is something like the following...
Hi, I'm not 100% sure this is only a Hibernate issue as this might be a more abstract decision but I'll give it a try. Since the problem description is a bit lengthy I'll first state that what I'd like to do is see if I can change the implementation to something which more resembles a Best practice implementation then this. I have 3 ent...