many-to-many

If I have two objects that have a many-to-many relationship, I would typically model them in my database schema with a many-to-many table to relate the two. But should that many-to-many table (or "join table") have a primary key of its own (integer auto-incremented)? For example, I might have tables A and B, each with an ID, and a table called A_B that has a foreign key tuple of (A_ID, B_ID). But should A_B have a primary key auto-incremented ID column of its own, or not? What are the advantages and disadvantages of adding it? I personally like natural keys for many-to-many joins. But what

I am having problems querying many-to-many relationships in Linq To Entities. I am basically trying to replicate this query using Linq: Select * FROM Customer LEFT JOIN CustomerInterest ON Customer.CustomerID = CustomerInterest.CustomerID LEFT JOIN Interest ON CustomerInterest.InterestID = Interest.InterestID WHERE Interest.InterestName = 'Football' I have looked around the net and not really found any suitable examples of how to do this. The closest I have got is: List<Customer> _Customers = (from _LCustomers in _CRM.Customer.Include("CustomerInterest.Interest") where _LCustomers

I have a mapping like this: @ManyToMany(cascade = CascadeType.PERSIST) @JoinTable( name="product_product_catalog", joinColumns={@JoinColumn(name="product_catalog", referencedColumnName="product_catalog")}, inverseJoinColumns={@JoinColumn(name="product", referencedColumnName="product")}) public List<Product> products = new ArrayList<Product>(); I can fetch the products for the catalog nicely, but I can't (dynamically) order the products. How could I order them? I probably have to write a many-to-many HQL query with the order-by clause? I though of passing the orderBy field name string to the

I have a many-to-many (developers & projects) relationship modeled using SA's association_proxy . The collections (developers on each project & projects for each developer) work fine, but I need to filter on an attribute of the association itself (status). Something like this (which does not work): activeDevelopers = s.query(Developer).filter_by(Developer.developerProjects.status == 'active').all() What am I missing? Here is the complete test code: import logging from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey from sqlalchemy.orm import relation,

I have pored through StackOverflow, Google and asp.net trying to find a clear cut, basic example of how to do this. All the examples have been abstract or involved complications that do not apply. I haven't been able to extract much useful from them. So far, none of them have completely answered my question or addressed my issue(s). I am working on an MVC project with the following model: Article.cs: public class Article { public int ArticleId { get; set; } public string Title { get; set; } . . . public virtual ICollection<Category> Categories { get; set; } public Article() { Categories = new

I have a model MyModel2 with a ManyToManyField related to another model MyModel1 . How can I get the pairs mymodel1.id, mymodel2.id , as represented in the table Django create for this relation? Do I have to do a raw SQL query on this table or is it possible through the object managers of this models? class MyModel1(models.Model): name = models.CharField(max_length=50) class MyModel2(models.Model): name = models.CharField(max_length=50) mymodel1 = models.ManyToManyField(MyModel1) This is the many to many field instance: MyModel2.mymodel1 This is the intermediary table model: MyModel2.mymodel1

In my Symdony2 project I've two related entities: Service and ServiceGroup. This should be many-to-many relationship, because each group can have many services, and each service can belongs to many groups. Moreover, I need a user interface to manage services and groups. So, when editing a Service, user should be able to choose to which groups it belongs. Analogously, when editing a ServiceGroup user should be able to choose which services belongs to this group. I've already achieved this by setting up a Many-To-Many relation in my Doctrine entites. Everything is working like a charm, including