class Project
  belongs_to :category
  belongs_to :fondation
  has_many :project_eligibles
  has_many :eligibles, through: :project_eligibles
end

class Category
  has_many :projects
  has_many :alerts
end

class ProjectEligible
  belongs_to :project
  belongs_to :eligible
end

class Alert
  belongs_to :user
  belongs_to :category
  belongs_to :eligible
end

class ProjectMailer < ApplicationMailer
  def newproject(project)
    @project = project
      mail(
        to:       mails = User.joins(:alerts).where(alerts: {category_id: project.category_id}).collect(&:email).join(","),
        subject:  "New project for you !"
      )
  end

end

class ProjectsController < ApplicationController
  def create
    @project = Project.new(project_params)
    if @project.save
      ProjectMailer.newproject(@project).deliver_now
      redirect_to projects_path
    else
      render :new
    end
  end
end

def newproject(project)
    @project = project
      mail(
        to:       mails = User.joins(:alerts).where(alerts: {eligible_id: project.project_eligibles.where(:eligible_ids)}).collect(&:email).join(","),
        subject:  "New project for you !"
      )
  end

end