many-to-many

I know many:many isn't supported in Linq2Sql but I am working on a workaround I am working with my little SO clone and I have a table with Questions and a table with Tags and a linking table QuestionTag so I have a classic many:many relationship between Questions and Tags. To display the list of Questions on the front page I have this class I want to fill up from a Linq2Sql query public class ListQuestion { public int QuestionID { get; set; } public string Title{ get; set; } public IEnumerable<Tag> Tags { get; set; } } public IEnumerable<ListQuestion> GetQuestions() { from q in Questions .....

I have two tables with the many-to-many association. — DB fragment: loads Id Name sessions Id Date sessionsloads LoadId SessionId — Hibernate mapping fragments: /* loads.hbm.xml */ <set name="sessions" table="sessionsloads" inverse="true"> <key column="LoadId" /> <many-to-many column="SessionId" class="Session" /> </set> … /* sessions.hbm.xml */ <set name="loads" table="sessionsloads"> <key column="SessionId" /> <many-to-many column="LoadId" class="Load" /> </set> In order to remove one entry from the association table sessionsloads , I execute this code: Session session = sessionDao.getObject

Context We're building a blog for an intro. to databases course project. In our blog, we want to be able to set Labels on Posts . The Labels can't exist by themselves, they only do so if they are related to a Posts . This way, Labels that are not used by any Posts shouldn't stay in the database. More than one Label can belong to a single Post , and more than a single Post can use a Label . We are using both SQLite3 (locally/testing) and PostgreSQL (deployment). Implementation Here is the SQL (SQLite3 flavor) that we use to create those two tables, along with the relationship table: Posts

In a typical many-many arrangement like this... Movies Actors Movies_Actors ------ ------ ------------- movie_ID actor_ID FK_movie_ID title name FK_actor_ID ... how should the association table ( 'Movies_Actors' ) be indexed for optimal read speed? I usually see this done only with the composite primary key in the association table, like so: CREATE TABLE Movies_Actors ( FK_movie_ID INTEGER, FK_actor_ID INTEGER, PRIMARY KEY (FK_movie_ID, FK_actor_ID) ) However, this seems like the index will only be useful when searching for both movie_ID and actor_ID (although I'm not certain on whether a

I have three models: products , users , and reviews . A review is linked to a product and a user as follows: class Review(models.Model): product = models.ForeignKey(Product) user = models.ForeignKey(User) review_text = models.TextField() creation_date = models.DateTimeField(auto_now_add=True) I'd like to allow each user to submit only one review per product. What is the recommended way to achieve this? Through the model, through verification, or something else? I'm very new to Django/Python. Thanks. Use unique_together to make sure that each user/product combination is unique: class Review

The context I have a simple association between two entities - Category and Email (NtoM). I'm trying to create web interface for browsing and managing them. I have a simple e-mail subscription edit form with list of checkboxes that represents categories, to which given e-mail belongs (I registered property editor for Set<Category> type). The problem Form displaying works well, including marking currently assigned categories (for existing e-mails). But no changes are saved to EmailsCategories table (NtoM mapping table, the one defined with @JoinTable - neither newly checked categories are added

Lets take StackOverflow questions as example. Each of them has multiple tags assigned. How to build an algorithm that would find related questions based on how many common tags they have (sorted by number of common tags)? For now I can't think about anything better than just selecting all questions that have at least one common tag into an array and then looping through them all assigning number of common tags to each item, then sorting this array. Is there more clever way of doing it? Perfect solution would be a single sql query. This could be as bad as O(n^2), but it works: create table

For a Symfony2 project I had to create a relationship between a blog post and so called platforms. A platform defines a specific filter based on the domain you use to view the site. For example: If you join the site by url first-example.com, the site will only provide blog posts, which are connected to this specific platform. To do so, I created two entities Post and Platform. Afterwards I mapped them together with a Many-To-Many relationship. I'm trying to retrieve data via this Many-To-Many relationship from the builtin function findBy() in Doctrines' EntityRepository . // every one of these