In a many to many relationship, the primaryjoin expression describes the join between the left table and the junction table, and the secondaryjoin describes the join between the junction table and the right table. In other words, the primaryjoin expression is saying, “find all rows in the followers table where follower_id is X”, the secondaryjoin … Read more
Here is what i ended up doing. I hope it helps someone. INSERT INTO persons (firstname,lastname) VALUES (‘John’,’Doe’); SET @person_id = LAST_INSERT_ID(); INSERT IGNORE INTO properties (property) VALUES (‘property_A’); SET @property_id = LAST_INSERT_ID(); INSERT INTO has_property (person_id,property_id) VALUES(@person_id, @property_id); INSERT IGNORE INTO properties (property) VALUES (‘property_B’); SET @property_id = LAST_INSERT_ID(); INSERT INTO has_property (person_id,property_id) VALUES(@person_id, … Read more
Here is how to find all the changed many-to-many relationships. I’ve implemented the code as extension methods: public static class IaExtensions { public static IEnumerable<Tuple<object, object>> GetAddedRelationships( this DbContext context) { return GetRelationships(context, EntityState.Added, (e, i) => e.CurrentValues[i]); } public static IEnumerable<Tuple<object, object>> GetDeletedRelationships( this DbContext context) { return GetRelationships(context, EntityState.Deleted, (e, i) => e.OriginalValues[i]); … Read more
Why are you talking about tables? Are you creating an object model or a database model? For an object model, there’s no reason a Dog can’t have a List<Owner> and an owner have a List<Dog>. Only if you have attributes on the relationship do you need an intermediate class (what UML calls an Association Class). … Read more
Standard way is to load the artist including the current related types from the database and then remove the types with the selected Ids from the loaded types collection. Change tracking will recognize which types have been removed and write the correct DELETE statements to the join table: var artist = this._db.Artists.Include(a => a.ArtistTypes) .SingleOrDefault(a … Read more
If you want to add queryset to bulk add or remove method of many to many relation models : qs = Article.objects.all() publications = Publications.objects.get(id=1) publications.article_set.add(*qs) publications.save() publications.article_set.remove(*qs) publications.save()
Django does not support compound primary keys. You can create a single compound unique key with Meta.unique_together.
The semantic of the relationship doesn’t look right. I think it should be something like: class Restaurant(db.Model): … dishes = db.relationship(‘Dish’, secondary=restaurant_dish, backref=db.backref(‘restaurants’)) Then, to retrieve all the dishes for a restaurant, you can do: x = Dish.query.filter(Dish.restaurants.any(name=name)).all() This should generate a query like: SELECT dish.* FROM dish WHERE EXISTS ( SELECT 1 FROM restaurant_dish … Read more
Here’s the UNION approach I hinted at on the mailing list earlier today. from sqlalchemy import Integer, Table, Column, ForeignKey, \ create_engine, String, select from sqlalchemy.orm import Session, relationship from sqlalchemy.ext.declarative import declarative_base Base= declarative_base() friendship = Table( ‘friendships’, Base.metadata, Column(‘friend_a_id’, Integer, ForeignKey(‘users.id’), primary_key=True), Column(‘friend_b_id’, Integer, ForeignKey(‘users.id’), primary_key=True) ) class User(Base): __tablename__ = ‘users’ id … Read more