解决数据库关系循环

Question

在数据库中我有这样一个模型：

客户可以租车，也可以租车。如您所见，Car 具有 OwnerID - 拥有汽车的客户，但同时客户也可以从其他车主那里租用汽车，因此在订单 table 中，他显示为用户。
那么如何更改模型以避免此类循环，甚至可能吗？

Answer 1

根据我的理解，我认为所有者（出租汽车的人）和租户（租车的人）有两个单独的个人资料并分别登录会更好

User      Owner      Tenant     Order
------    ------     -------    -------    
id        owner_id   tenant_id  owner_id 
email     user_id    user_id    tenant_id 
                                car_id

希望对您有所帮助！

Answer 2

考虑识别（存储在表中）

所有者是谁，他们拥有什么，
客户是谁。

.

create table persons (
  -- I prefer "people". YMMV.
  person_id integer primary key,
  person_name varchar(25) not null
  -- Other columns go here.
);

create table cars (
  -- VIN might be a better choice.
  car_id integer primary key
  -- Other columns go here.
);

create table car_owners (
  -- Only car owners known to us can rent out a car.
  car_id integer not null
    references cars(car_id),
  owner_id integer not null
    references persons (person_id),
  primary key (car_id, owner_id)
  -- Other columns go here.
);

create table customers (
  -- Any person can rent a car. (But some persons are not customers.)
  customer_id integer primary key  
    references persons (person_id)
  -- Other columns go here.
);

create table rentals (
  customer_id integer not null
    references customers (customer_id),
  car_id integer not null,
  owner_id integer not null,
  primary key (customer_id, car_id, owner_id),

  -- Don't rent a car unless we know who the owner is.
  foreign key (car_id, owner_id)                  
    references car_owners (car_id, owner_id)

  -- Other columns go here.
);

解决数据库关系循环

Resolve the database relationship cycle

database

database-design

foreign-keys

database-relations