Advantages and disadvantages of Ruby on Rails polymorphic relationships.

Question

What advantages and disadvantages do you know of Ruby on Rails polymorphic relationships.

Answer 1

Advantages:

• You can link anything to anything quite easily
• Adaptable relationships help accommodating unforeseen circumstances
• Very easy to implement relationships
• Great for ad-hoc systems

Disadvantages:

• Foreign keys not practical
• Indexes include another dimension of complexity
• Relationships between tables hard to identify when using STI
• Database diagramming tools cannot interpret
• Not always practical for join models
• Strongly discouraged for systems where data integrity must be verified

I'm a big fan of using relationships of this sort for records that are attached to a large number of things as required, for example, a comment or annotation record which may apply to a wide variety of records.

It is not very well suited for situations where the relationship is exercised in a JOIN frequently. That is, the polymorphic association should not be in the middle of a relationship between records, but as something on the perimeter.