In Rails, Join and Includes are both methods used to handle associations between models.
Difference:
The main difference is that includes eager loads the data into memory. So, when fetching multiple records from the tables, it doesn't fire multiple queries to the database; instead, it fetches the records already loaded in memory. This reduces the load on the database. However, it's important to wisely choose between joins and includes based on the specific requirements and context of your query.
Use Includes over Join:
- when you want to eager load associated records to avoid N+1 query problems.
- when the data is small that won't overload the memory.
- when the data doesn't change very frequently or until an operation is performed on the data loaded into memory.
Use Join over Includes:
- when you DO NOT need to load the entire associated records.
- when your query involves complex conditions that need to be applied to the associated models.
- when you just need to filter or perform calculations based on them.