Getting values through relational table - ruby-on-rails

Question

In my app I have a page which render all the projects in the database. What I want is to be able to filter the results, for example by showing only the once in which the user is a member.
Below is from my projects controller, where I want to do exactly that (show only projects where the user is a member). What do is to first get all the projects from 'ProjectUser' where the user_id is found. Then I want to use this array to retrieve all the relevant projects from the table 'Projects', with the use of #user_is_member.project_id.
This does not work because it only give me ONE project, not all.
How can I change the code so I accomplish what I want?
The code:
#user_is_member = ProjectsUser.where(:user_id => current_user.id)
#user_is_member.each do |member|
#projects = Project.where(:id => member.project_id)
end
Tables:
projects_users:
project_id
user_id
projects:
id
...non relevant fields...
Models:
User model:
class User < ActiveRecord::Base
has_many :project_users
has_and_belongs_to_many :projects
end
Project model:
class Project < ActiveRecord::Base
has_and_belongs_to_many :users # => , :class_name => 'User'
belongs_to :user
end
ProjectUser model:
class ProjectsUser < ActiveRecord::Base
belongs_to :user
belongs_to :project
end
Note: current_user is the currently logged in user (which has access to all the user fields, e.g "id")

Answer 1

This is not a good way to associate the models. If you want to associate user to project and make one user to admin/creator then you should associate your models as:
User
class User < ActiveRecord::Base
attr_accessible :first_name, :last_name, :email, :password
has_secure_password
has_many :projects_users
has_many :projects, :through => :projects_users
end
Project
class Project < ActiveRecord::Base
has_many :projects_users
has_many :users, :through => :projects_users
end
ProjectsUser
class ProjectsUser < ActiveRecord::Base
attr_accessible :role
belongs_to :user
belongs_to :project
end
I have added an extra column/attribute to your ProjectsUser Model that will have a string value (admin/member). And now you can get the members for a project by doing #project.users.where(:role => 'member') and admin by #project.users.where(:role => 'admin').first.
If you don't want to change your way then in your controller do something like:
#user_is_member = ProjectsUser.where(:user_id => current_user.id)
project_ids = []
#user_is_member.each do |member|
project_ids << member.project_id
end
#projects = Project.where(:id => project_ids)

Answer 2

If you want all the projects for the current_user, you can just do:
#projects = current_user.projects
I am assuming you have something like:
class User < ActiveRecord::Base
has_many :project_users
has_many :projects, :through => :project_users
end
class ProjectUser < ActiveRecord::Base
belongs_to :user
belongs_to :project
end
class Project < ActiveRecord::Base
has_many :project_users
has_many :users, :through => :project_users
end

Answer 3

The problem is that you have no project_id for some user which is somehow deleted.
Check your database that which project_id is nil by putting puts like statements in a loop.
Alternatively, you can use :dependent => :destroy on your relationship to get rid of such inconsistent data. It usually happens while you are testing and somehow delete any record but forget to delete the foreign key association relation for other table.
This can be accomplished like following:
#user_is_member = ProjectsUser.where(:user_id => current_user.id)
#user_is_member.each do |member|
puts "Checking the project id existence for each user member"+member.project_id.to_s
end