Rails Single Table Inheritance (STI) Simplifying Code and Improving Performance

Understanding Single-Table Inheritance (STI)

Single Table Inheritance (STI) is a database design pattern that allows multiple subclasses to be stored in a single database table, sharing a common schema. In STI, a parent class defines the common attributes and behavior, while the child classes inherit from the parent and extend or override its functionality.

To implement Single Table Inheritance (STI) in Rails, a crucial step involves adding a "type" column to the table representing the parent class. This additional column stores a string value that signifies the specific subclass of the parent class for each row. Rails automatically handle the mapping between the class hierarchy and the "type" column. This automation enables you to seamlessly query and manipulate the data, utilizing the inheritance structure established by STI.

The following is an example of Single Table Inheritance:

STI Pros & Cons

Using Single Table Inheritance (STI) in your Rails application offers several benefits:

• Simplified Code: STI allows you to eliminate redundant code by defining common attributes and behavior in a single parent class. This reduces duplication and improves maintainability, as changes made to the parent class automatically apply to all child classes.
• Database Efficiency: STI enhances performance by minimizing the need for multiple database tables. By storing related entities in a single table, the complexity of join operations is eliminated. This streamlined approach enables faster queries and enhances overall database performance.
• Polymorphic Associations: STI integrates smoothly with Rails' polymorphic associations, enabling the establishment of associations between various subclasses and other models. This level of flexibility allows for the creation of relationships without requiring additional join tables or intricate queries.

While STI offers advantages, it's essential to consider potential drawbacks:

• Schema Rigidity: STI relies on a single database table, which means all subclasses share the same attributes and columns. If you need to add specific attributes to a subclass, you may need to alter the table schema, potentially impacting other subclasses. This can make it challenging to evolve the data model as requirements change over time.
• Increased Table Size: As more subclasses are added, the size of the table representing the parent class grows. This can lead to increased storage requirements and slower queries when retrieving data from the table.

Understanding Polymorphic Associations

Polymorphic Associations provide an alternative approach to handle relationships between entities in Rails. With polymorphic associations, a model can belong to more than one other model on a single association. This allows for greater flexibility when establishing relationships between different entities.

Consider building a messaging application where users can send messages to each other. Now, you want to enhance the functionality by enabling users to send messages not only to other users but also to groups or events. How can you establish the relationships between messages and these various entities?

This is where Polymorphic associations comes into play. It have the benefit of establishing a single relationship between a message and its sender, regardless of whether the sender is a user, group, or event. This removes the requirement for the message model to have distinct affiliations for each type of sender and enables for dynamic relationships with any of them.

In Rails, implementing polymorphic associations involves using both foreign keys and type columns. The foreign key is responsible for storing the associated record's ID, while the type column is used to identify the specific model type associated with the record.

Polymorphic Associations Pros & Cons

Polymorphic Associations offer specific benefits:

• Flexible Relationships: Polymorphic associations offer the advantage of associating a model with multiple other models, providing flexibility in handling complex relationships. This eliminates the requirement of defining separate associations for each specific relationship, streamlining the codebase and reducing redundancy.
• Evolving Data Model: Polymorphic associations offer the advantage of easily adding new associations without the need to modify the existing table schema. This aspect provides developers with enhanced flexibility and agility, allowing for seamless evolution of the data model to cater to changing requirements.

However, there are potential downsides to using polymorphic associations:

• Performance Overhead: Polymorphic associations may result in more complex queries, leading to potential performance overhead. Joining multiple tables can introduce additional overhead compared to the simpler structure of STI.
• Increased Complexity: Managing polymorphic associations can introduce complexity to the codebase, particularly when handling multiple levels of associations. It demands careful management and can progressively become challenging to navigate and comprehend as the application scales.

When to use STI or Polymorphic Associations / Final Thoughts

Deciding whether to use Single Table Inheritance (STI) or Polymorphic Associations depends on the specific requirements of the application. Here is a comparison between the two methods.

STI is a technique that allows storing different types of objects in a single database table, distinguishing them through a type column. This approach is beneficial when subclass objects share most attributes and behavior with the superclass but also have some distinct properties. For instance, consider an e-commerce system that deals with various product types like electronics, books, and clothing. These types may share common attributes such as name, description, and price, while also possessing unique characteristics. By implementing STI, you can create a "products" table with shared columns, and each product type can have its own additional columns within the same table. This simplifies querying and reduces the number of tables required in the database.

Polymorphic Associations are useful when you need to associate multiple models with a single model, each with its own unique set of features. Consider a "Comment" model in a social media application, where comments may be made on various entities such as posts, photos, and videos. Despite the fact that these entities have distinct properties, you want to put all comments in a single database. You may establish a "comments" table that references the multiple object types by implementing polymorphic associations, allowing you to store comments for posts, photos, and videos in a single table. This method streamlines the database structure, reduces the need for duplicate tables, and provides for greater flexibility and scalability in connection definition.