Rails: Structuring a query involving a polymorphic association and STI?
You are providing the association to comments on the Upload class. Photo, which is inheriting from Upload will have this association through inheritance. Since the comments method is available on both the Upload instance, and on the Photo instance, you can write the following method to retrieve the comments: app/models/upload.
Rb def latest_comments(count=10) self.comments. Order("created_at DESC"). Limit(count) end This will join to the comments table using the type "Upload" when working with an instance of Upload, and it will join using the type "Photo" when using working with instances of that class.
Rails will automatically handle the join to the comments table using the class name when going through the comments association.
You are providing the association to comments on the Upload class. Photo, which is inheriting from Upload will have this association through inheritance. Since the comments method is available on both the Upload instance, and on the Photo instance, you can write the following method to retrieve the comments: # app/models/upload.
Rb def latest_comments(count=10) self.comments. Order("created_at DESC"). Limit(count) end This will join to the comments table using the type "Upload" when working with an instance of Upload, and it will join using the type "Photo" when using working with instances of that class.
Rails will automatically handle the join to the comments table using the class name when going through the comments association.
Thanks for the reply Ben, but my model specifies that only Photos, and not Uploads, are commentable. It greatly simplifies things if the superclass Upload is given the association has_many :comments, but I don't want to break my model by doing this. If I don't want to disrupt my model in that way, is what I want to achieve actually possible without a long chained query, I wonder?
– JamesDS Jul 10 at 22:49.
I'm trying to find the 10 most recent comments on photos so I can integrate them into an activity feed on my Rails 3.0.3 application. So far so good, right? The problem comes when I try to construct a query.
This code works on my development machine with SQLite, but I've had to make some changes to get it to work on the production server using PostgreSQL. The above incarnation of the query hasn't been tested on the production server yet, but I was looking for a cleaner way of structuring the query, as the above doesn't feel very robust, nor does it seem very 'Railsy'. I came upon a post on StackOverflow that described a different way of querying a polymorphic association.
However, this doesn't work for STI: since Photo is inheriting from Upload, I can't directly fetch the comments pertaining to photos - only the comments for all classes inheriting from Upload. I've looked at a fair number of other posts relating to either polymorphism or STI, but none combine the two in the way I'm looking for. I could just muddle around with the initial query, but does anyone have any thoughts on alternative ways to structure a query involving polymorphism and STI?
Edit: I found another question on here along the same lines as mine. Unfortunately, the top answer didn't provide the solution I'm looking for. If I were to apply it to my problem I'd be moving the has_many :comments association from the Photo model to the Upload model, and adding some code to the Comment class to determine the correct class of commentable.
This isn't ideal as it breaks the modelling in that any subclass of Upload will have comments. There must be a better way...?
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.
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