在Postgre中设计多个1对1关系的最佳方法是什么

Question

I would like to know if there's a better way to design this kind of relationships within Postgre:

Basically, I've got some entities that are either an EntityA , an EntityB or an EntityC . I will have plenty of other relationships between entities and other stuff (like Comment in this case) so I've got this generic Entity that defines which type of Entity it's linked to.

As an example, if we have an EntityA linked to a comment, the Entity entry will look like: type: EntityA entity_a_id: x entity_b_id: null entity_c_id: null

Is there a better way to design this?

Answer 1

This seems a good fit for the Table Inheritance feature

CREATE TABLE entity (
  -- columns that are shared among all entities
);

CREATE TABLE entity_a (
  -- columns that are unique for this entity type
) INHERITS (entity);

CREATE TABLE entity_b (
  -- columns that are unique for this entity type
) INHERITS (entity);

This way, entity types do not include columns of other types

Answer 2

How different are the entities?

Why not just

CREATE TABLE Entity
(
    EntityId int,
    EntityType enum(A, B, C),
    FieldValue varchar(255)
) 

or if the field values are significantly different and don't make sense in a single column,

CREATE TABLE Entity
(
    EntityId int,
    EntityType enum(A, B, C),
    FieldValueX varchar(255),
    FieldValueY varchar(255),
    FieldValueZ varchar(255)
)