I have two models that are associated with has_and_belongs_to_many, and I'm trying to create a method that computes something with attributes from both models, but I'm getting an undefined method error with the code I'm using below. What am I missing?
Model_1.rb
Class Model_1 < ActiveRecord::Base ... has_and_belongs_to_many :model_2
def some_method attr_1 * Model_2.find(model_2_id).attr_I_need end
If the relationship is HABTM, you won't have a model_2_id attribute to find by, there should be a join table.
If you explain in a little more detail what problem you're trying to solve with your relationship and the mathematical operation between them, maybe a solution can be suggested.
Hi Michael,
Thanks for the reply.
I actually have created the join table as documented in the rails guides, with the right naming convention and all. It's got a model_1_id and a model_2_id, and an index
Sure, I can give some more details. I'm creating a golf application that let's users enter in some information about their golf game, and then shows them appropriate golf courses.
So I've got one model called 'Course' that is just a bunch of seed data. Then I've got another model called 'Player' that contains all the user-entered information via a form.
Ultimately, I have a Player 'show' view that shows a table with the appropriate golf courses, along with some other information. One of these other pieces of information is a mathematical function that compares the user's entered handicap with the course's.
So all of my methods are in the Player model, and for this handicap function, I'm trying to pull in the Course's handicap attribute to do the math.
Hope that makes sense
Sa S. wrote in post #1074685:
Hi Michael,
Thanks for the reply.
I actually have created the join table as documented in the rails guides, with the right naming convention and all. It's got a model_1_id and a model_2_id, and an index
Sure, I can give some more details. I'm creating a golf application that let's users enter in some information about their golf game, and then shows them appropriate golf courses.
So I've got one model called 'Course' that is just a bunch of seed data. Then I've got another model called 'Player' that contains all the user-entered information via a form.
Ultimately, I have a Player 'show' view that shows a table with the appropriate golf courses, along with some other information. One of these other pieces of information is a mathematical function that compares the user's entered handicap with the course's.
So all of my methods are in the Player model, and for this handicap function, I'm trying to pull in the Course's handicap attribute to do the math.
Rails provides methods for accessing associations between models. You should not need to use foreign keys directly as shown in your original post.
Given: 1. Player has many courses 2. Course has many players
Example: a_player = Player.first players_courses = a_player.courses player_courses.each do |course| puts course.handicap end
class Player def recommended_courses Course.where(courses[:handicap].gt(a_player.handicap)) .and(courses[:handicap].lt(a_player.handicap) end end
These examples are for demonstration only. They are completely untested or checked for syntax.
Robert Walker wrote in post #1074687:
class Player def recommended_courses Course.where(courses[:handicap].gt(a_player.handicap)) .and(courses[:handicap].lt(a_player.handicap) end end
Just realized after posting that this is a silly example, but should get you on the right track.
Should have been something like .... courses[:handicap].gt(a_player.handicap - 5).and(courses[:handicap].lt(a_player.handicap + 5))
Sorry I don't know anything about golf, so that may still sound ridiculous from the perspective of a golf handicap. I hope it at least helps with the programming issue.
Thanks for the help! Although I'm not sure I totally understand it, still a bit of a noob. So if I wanted to do something as simple as subtract the user's handicap from the course's handicap, how would I create a method for that in the Player model? (sorry maybe you might have done it already but I'm not sure what .gt and .lt mean)
Basically something like
class Player
def handicaps_difference Course.handicap - handicap (from the player) end
Sa S. wrote in post #1074690:
Thanks for the help! Although I'm not sure I totally understand it, still a bit of a noob. So if I wanted to do something as simple as subtract the user's handicap from the course's handicap, how would I create a method for that in the Player model? (sorry maybe you might have done it already but I'm not sure what .gt and .lt mean)
Basically something like
class Player
def handicaps_difference Course.handicap - handicap (from the player) end
Given that with a many-to-many relationship (has_and_belongs_to_many) a single player will be associated to many courses and one course will be associated to many players. So in order to do that sort of math you'll need to iterate through them.
Player will have a method, added by ActiveRecord named "courses"...
a_player.courses
I assume here that you want to first select a player:
a_player = Player.find(:id)
Then I assume you want to list all the courses associated with this one player with the handicap difference:
a_player.courses.each do |course| puts course.handicap_difference(a_player) end
Where each course can calculate the handicap difference with a given player:
class Course def handicap_different(player) player.handicap - self.handicap end end
But even better would be to expose the join table with its own object using has_many :through. Then you can put the calculation in the object that "knows" about both sides:
class CourseAssignment # The exposed join table has_one :player has_one :course
def handicap_difference player.handicap - course.handicap end end
Again the "player" and "course" methods will be added by ActiveRecord to the CourseAssignment object.
Sa S. wrote in post #1074690:
Thanks for the help! Although I'm not sure I totally understand it, still a bit of a noob. So if I wanted to do something as simple as subtract the user's handicap from the course's handicap, how would I create a method for that in the Player model? (sorry maybe you might have done it already but I'm not sure what .gt and .lt mean)
Forgot to mention ".gt" and ".lt" means "greater than" and "less than" respectively.
Okay great, thanks! I think I'll actually trying doing this in the join table. I guess my last question would be how would I call that method from that join table in let's say the Player show view?