I am trying to record which admin manages which order, but both order and manage are a relationship, can I connect both of them as the picture suggest?
I saw an article that says that this is not standard practice and is not recommended, if so anyway i can improve this?
My ERD
Two relations can be connected using the "Aggregations"
Aggregation allows us to treat a relationship set as an entity set for purposes of participation in (other) relationships.
Related
I would like to create a new app rails but being a beginner it's been several days that I try several possible ways without really finding the right one, I just managed to do something but I'm not sure that it's perfect in terms of relationships. the concept would be that people could either create or participate in meals. I would like the ingredients to be reusable, but their attributes such as the origin or cooking method can be modified in each case. do you think this style of rallying is fair?
or
The second option is a classic one. Stick to using many-to-many relation in that cases.
Though it is better to have one-to-many relation between specification and menu - like several specifications for each menu. And specification should also contain ingredient_id.
I have 3-4 different types of clients for a photo site. Musician, wedding, portrait, and general with the possibility of adding more types. The idea is each type will have a shared set of attributes such as name email etc. but each will have their own too.
Musicians will have band name, members, genre, while wedding will have venue, coordinator details and so on.
I think this is the right way to go about it, correct me if there's an easier way to track multiple shared and unique attributes.
I was reading up on single table inheritance and one place said to use it only if the models have the same attributes but different behavior. How can I structure my models to meet this? From a more generic OOP standpoint this makes a lot of sense to me, but I'm having doubt's from that clause of STI.
Your use case sounds like a good one for STI. The key thing is that the children share some attributes with their siblings, not all attributes. I found this overview helpful:
http://samurails.com/tutorial/single-table-inheritance-with-rails-4-part-1/
I have a many-to-many relationship between two models: Customers and Products. Many customers share the same database of products.
My questions is, what if I want to store Customer specific data for each product. Like how many are in stock? My first instinct is to create some kind of wrapper model (e.g. Inventory) that refers to a product but would be customer specific. Is there a better way to do this?
Glad I could be of help.
Original Answer:
Have you considered using a has many through association
I have created the following tables in my application - roles, permissions and permissions_roles. Roles HABTM permissions, and permissions HABTM roles. I have seen many tutorials on setting up all of the tables/models etc for the 3 tables and defining the relationship, but I haven't been able to find anything on actually maintaining the relationship -- What is the best practice -- set up a third controller/set of views?
I want to be able to create Roles/Permissions independently of the relationship, ie make the assignment later - If I create a new role, I may need to go back and assign existing permissions to it (or vice-versa).
I know there are plenty of plugins that do this sort of thing, but I really want to see if I can learn more by starting from the ground up...
Thanks
Its a little bit dated, but should still work, I shudder at the verbosity of the code but it was one of the first things I did in Rails...
http://blog.wolfman.com/articles/2006/5/20/role-based-authentication-admin-page
Given you have to implement a news feed like the one seen in social networks, ex facebook.
Currently I'm using a News class which has a polymorphic assocation which can be of any kind like Image, Comment, Friendship, GroupMembership, etc. Whenever an Object is created, as News is created too. It's working fine with AR(ActiveRecords) but I get into trouble when I'd switch to DM(DataMapper) or Sequel as both don't natevily support polymorphic associations and discourage it's usage.
One workaround would be to use a big SQL clause with lot's of UNIONs to merge all the different tables which should be considered as news. But this has some drawbacks, escpecially performance would be terrible.
So I wonder how to solve without polymorphic associations while still getting good performance and no other drawbacks, like having the possibility of adding meta data to a news?
Disclaimer: I'm the lead developer of Sequel.
The best way to go about it usually depends on what types of things you want to do with the data. One way to go about it is to have foreign key columns for all possible relationships:
news:
id
... (Other columns)
image_id
comment_id
friendship_id
group_membership_id
There is really no performance difference in doing things this way versus having a generic foreign key and storing a class name. For lazy loading, you just pick the one foreign key field that's not nil/NULL, and choose the appropriate association to load. For query-per-table eager loading, you just load all associations at once. This also is more flexible in that you can eagerly load using JOINs, which isn't possible with the polymorphic approach. Plus, you get the benefit of real referential integrity.
The one downside is that if you want to add more association types in the future, you need to add foreign keys to the table.
Here's a gem to maintain the referential integrity of Polymorphic Associations at the database level in Rails:
https://github.com/mkraft/fides
As of this posting there are adapters for SQLite3 and Postgresql.
Disclaimer: I wrote the gem.