Rails驗證-在創建子模型時驗證父模型

Question

假設我有ParentModel是HAS_MANY ChildModel 。

有沒有一種在創建ParentModel時檢查（ 驗證 ） ParentModel的方法（例如，檢查是否存在同名子代記錄？

Answer 1

這很簡單，如果有誤，請糾正我。

def Parent 
    has_many :children 
end 
def Child
    belongs_to :parent
    #Here you could run some validations, for example:
    validates :name,presence: true, length: { minimum: 1 },uniqueness: { scope: :parent_id }
    #by running uniqueness with scope, you can repeat names, but not associated with the same parent. 
end 

然后可以例如：

p = Parent.first #suppose we already have the parent
p.child.new  #create a child, with attributes if needed 
p.valid? #p won't be valid unless his new child is

替代方案：

p = Parent.first #suppose we already have the parent
c = Child.new  #create a child, with attributes if needed 
p.children << c #append the child to the collection, if C is invalid, then it won't be saved into the database
p.valid?   #validate,