如何将has_one关联限制为单个记录 [英] How to limit has_one association to a single record

问题描述

我无法在has_one关系中仅保留一条记录

I am having trouble with retaining only a single record in a has_one relationship

示例

类别和问题

问题属于一个类别，以及一个类别有一个问题

A question belongs_to a category, and a category has_one question

实际上，尽管存在has_one关系，但我正在构建的系统中看到的情况是，我有多个属于一个类别的问题.

In reality as seen in a system i am building even though the has_one relationship exists, there comes a case where i have multiple questions that belong to a category.

has_one关系不应该将它们限制为仅一条记录吗?如果没有，那么我如何确保我始终保持一份记录?

Shouldn't the has_one relationship limit them to just one record? If not, then how can i make sure that i always keep one record?

编辑

请注意，问题模型对类别ID具有唯一性规则，并且仍然我发现多个记录的案例指向相同的类别ID.

Please note that question model has a uniqueness rule on the ID of category and STILL i found cases of multiple records that point to same category ID.

那怎么可能?

编辑2

模型概述

class Event < ApplicationRecord
    has_one :travel_time, :inverse_of => :event, dependent: :destroy
end

class TravelTime < ApplicationRecord
     belongs_to :event, :inverse_of => :travel_time
     validates_uniqueness_of :event_id, allow_nil: true 
end

编辑3

方法用于保存旅行时间记录

method in event model used to save the travel time record

def store_travel_times(body)
    travel_times = self.build_travel_time

    # get travel times
    ...

    if !travel_times.save
     logger.error "..."
    end
end

用于查找多个记录的查询

Query used to find the multiple records

 2017-05-04T13:39:15.277063 #50567] DEBUG -- :   TravelTime Load (0.4ms)  SELECT "travel_times".* FROM "travel_times" WHERE "travel_times"."event_id" = $1  [["event_id", 3105]]

推荐答案

如注释中所述，创建db级约束以检查列的唯一性并避免创建多个记录.您需要使用以下代码创建迁移文件:

As discussed in the comments, create db level constraint to check uniqueness of a column and avoid multiple records creation. You need to create a migration file with below code:

add_index :travel_times, :event_id, unique: true

希望有帮助.

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