Polymorphic Relationships

Polymorphic relationships refers to those elements in a database which could be related with more than one entity in the same relationship. This is possible when two or more entities can be related with other entities using just one middle table. In a regular relationship each one should have its corresponding middle table to relate with another entity.

Type of relationships

One to One

erDiagram
    %% ===================================
    %% UNO A UNO POLIMÓRFICA
     ===================================
    %% UNO A MUCHOS POLIMÓRFICA
    %% ===================================
    
    Article ||--o{ Comment : "has"
    Video ||--o{ Comment : "has"
    
    Article {
        int id PK
        string title
        text body
    }
    
    Video {
        int id PK
        string title
        string url
    }
    
    Comment {
        int id PK
        text content
        int commentable_id FK
        string commentable_type
    }

Many to Many

erDiagram
    %% ===================================
    %% MUCHOS A MUCHOS POLIMÓRFICA
    %% ===================================
    
    BlogPost ||--o{ Taggable : ""
    Product ||--o{ Taggable : ""
    Taggable }o--|| Tag : ""
    
    BlogPost {
        int id PK
        string title
        text content
    }
    
    Product {
        int id PK
        string name
        decimal price
    }
    
    Taggable {
        int id PK
        int tag_id FK
        int taggable_id FK
        string taggable_type
    }
    
    Tag {
        int id PK
        string name
    }