在同一列中引用外键

I'm designing a bd-scheme for mysql. My db stores 3 kinds of points: a, b or c and a path is composed by n pair of points:

我正在为mysql设计一个bd-scheme。我的数据库存储3种点:a,b或c,路径由n对点组成:

Route = [ (a1 or b1 or c1 ; a2 or b2 or c2), (a2 or b2 or c2 ; a3 or b3 or c3), ...]

路线= [(a1或b1或c1; a2或b2或c2),(a2或b2或c2; a3或b3或c3),...]

create table a_points (
    point_id    serial      not null,
    owner_id    bigint unsigned not null,
    name        varchar(20) not null,

    primary key (point_id),
    foreign key (owner_id) references othertable (other_id)
    ) engine = InnoDB;


create table b_points (
    point_id    serial      not null,
    owner_id    bigint unsigned not null,
    name        varchar(20) not null,
    fields      varchar(20) not null,


    primary key (point_id),
    foreign key (owner_id) references othertable (owner_id)

    ) engine = InnoDB;

create table c_points (
    point_id    serial      not null,
    name        varchar(20) not null,
    cfields     varchar(20) not null,

    primary key (point_id)
    ) engine = InnoDB;

create table paths (
    path_id serial          not null,
    name        varchar(20) not null,

    primary key (path_id)
    ) engine = InnoDB;

create table point_pairs (
    pair_id     serial      not null,
    path_id bigint  unsigned    not null,
    point_from  bigint unsigned not null,
    point_to    bigint unsigned not null,
    table_from  varchar(9)  not null,
    table_to    varchar(9)  not null,

    primary key (pair_id),
    foreign key (path_id) references paths (path_id)
    ) engine = InnoDB;

(*) a pair of point is (m, n) or from m to n

(*)一对点是(m,n)或从m到n

So I'm storing pair of points together with their path's id. My problem is that I had to create two columns identifying the tables' name of m and n. table_from for m and table_to for n. Thus I'd have to use these two columns in my code to know what kind of points are saved in a route (path and point_pairs table). My question: Does MySql provide something for referencing n foreign keys in the same column? I already thought about joining a, b and c point tables but I'd have to add a type column to this new table and my php classes would become useless.

所以我将它们的路径ID存储在一起。我的问题是我必须创建两列来标识表的名称m和n。 table_from表示m,table_to表示n。因此,我必须在代码中使用这两列来了解路径中保存了哪种点(path和point_pairs表)。我的问题:MySql是否提供了在同一列中引用n个外键的东西?我已经考虑过加入a,b和c点表但是我必须在这个新表中添加一个类型列,我的php类将变得无用。

Thanks in advance!

提前致谢!

1 个解决方案

#1

You're using a pattern called Polymorphic Associations, and no, there's no way to do that and use foreign keys to enforce referential integrity.

您正在使用一种称为多态关联的模式,不,没有办法,并使用外键来强制引用完整性。

I suggest you make one common table that a_points, b_points, and c_points reference. Then your point pairs can reference that common table.

我建议你创建一个a_points,b_points和c_points引用的公共表。然后你的点对可以引用该公共表。

a_points -->
b_points -->  common_points  <-- point_pairs
c_points -->

In other words, the way to make Polymorphic Associations work is to reverse the direction of the reference.

换句话说,使多态关联工作的方法是反转参考的方向。

#1