many-to-many

I am having problem with saving the changes to database. I am updating the model A in my controller, however when I save the changes using SaveChanges() I end up having a duplicated item in database for B. After the UpdateModel() is called I inspected the Bs property and it was as I expected however right after the SaveChanges() is called if I inspect the Bs property I will see that the Id is completely different (new Id and new entry). My class is similar to this: public class A { [HiddenInput(DisplayValue = false)] public int AId { get; set; } public string Name { get; set; } public virtual

I've setup a nested form in my rails 3.2.3 app, it's working fine, my models are: class Recipe < ActiveRecord::Base attr_accessible :title, :description, :excerpt, :date, :ingredient_lines_attributes has_and_belongs_to_many :ingredient_lines accepts_nested_attributes_for :ingredient_lines end and: class IngredientLine < ActiveRecord::Base attr_accessible :ingredient_id, :measurement_unit_id, :quantity has_and_belongs_to_many :recipes belongs_to :measurement_unit belongs_to :ingredient end As above, a Recipe can have multiple IngredientLines and vice versa. What I'm trying to avoid is record

I have the following tables(only listing the required attributes) medicine (id, name), generic (id, name), med_gen (med_id references medicine(id),gen_id references generic(id), potency) Sample Data medicine (1, 'Crocin') (2, 'Stamlo') (3, 'NT Kuf') generic (1, 'Hexachlorodine') (2, 'Methyl Benzoate') med_gen (1, 1, '100mg') (1, 2, '50ml') (2, 1, '100mg') (2, 2, '60ml') (3, 1, '100mg') (3, 2, '50ml') I want all the medicines which are equivalent to a given medicine. Those medicines are equivalent to each other that have same generic as well as same potency. In the above sample data, all the

I am working on a Google App Engine application and I am relatively new at this. I have built an app already in Django and have a model using a field type of ManyToMany. I am aware that django-nonrel does not support many-to-many field types of Django. So I am considering using ListField instead. Questions: - What is the implication of using ListField instead of ManyToMany? - I am aware that this means that Django's JOIN API cannot be used. But what does this mean for my app? - Am I going to have problems when it comes to doing a search for something in a many-to-many field? Apologies if these

I would like to use the single SQL-statement insert into T (...) select ... from T where ... to copy a lot of datasets. My problem is that there are N:M-relationships from table T to other tables and these have to be copied too. How can I do this, if I do not know which original dataset belongs to which copied dataset? Let me demonstrate by example. Content of the database before: Table T : ID | COL1 | COL2 ----------------- 1 | A | B 2 | C | D N:M-table references table U from table T (table U is not shown): T | U --------- 1 | 100 1 | 101 2 | 100 2 | 102 My copy operation where [???] is the