Question

我有两张桌子，里面有很多关联

的学生项目

通过表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

旧项目为空，new_projects不是

我在创建之前和之后放置了logger语句line（new_projects = students.projects），然后我可以看到区别。

但是当我把logger语句放在line（new_added_projects = new_projects - old_projects）之后检查old_projects，new_projects，newly_added_projects

然后old_projects等于new_projects

有人可以帮助我吗

Answer 1

我建议你在创建新项目之前和之后收集项目ID，并减去旧项目ID和新项目ID的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

Answer 2

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。不需要从旧计算它你已经在create_projects方法中有项目。

Rails变量数据正在发生变化

2 个答案: