Rails变量数据正在改变

Question

我有两个 table 具有多对多关联

学生项目

通过 table student_projects

连接

student = Student.find(1)
old_projects = student.projects

#Now Iam calling function that will create projects
create_projects

student = Student.find(1)
new_projects = student.projects
newly_added_projects = new_projects - old_projects

旧项目是空的，new_projects不是

我把记录器语句放在创建行之前和之后（new_projects = students.projects），然后我可以看到区别。

但是当我将记录器语句仅放在行后 (newly_added_projects = new_projects - old_projects) 检查 old_projects, new_projects, newly_added_projects

那么 old_projects 等于 new_projects

谁能帮我解决这个问题

Answer 1

student = Student.find(1)
old_projects = student.projects

newly_added_projects = create_projects # return newly projects from method itself.

def create_projects
  projects = []

  #add newly created projects in projects array and return at the end.
  return projects
end

做那样的事情。无需从旧计算它，您已经在 create_projects 方法中进行了项目。

Answer 2

我建议你在创建新项目之前和之后收集项目 ID，然后减去旧项目 ID 和新项目 ID，如下所示，

student = Student.find(1)
old_project_ids = student.projects.map(&:id) # You may use student.project_ids

#Now Iam calling function that will create projects
create_projects

student = Student.find(1)
new_project_ids = student.projects.map(&:id)
newly_added_project_ids = new_project_ids - old_project_ids

否则，您可以将 old_projects 对象从活动记录关系转换为纯 ruby 数组，如下所示，

student = Student.find(1)
old_projects = student.projects.to_a

#Now Iam calling function that will create projects
create_projects

student = Student.find(1)
new_projects = student.projects_to_a
newly_added_projects = new_projects - old_projects

Rails变量数据正在改变

Rails variable data is changing

ruby

ruby-on-rails

ruby-on-rails-3