Rails 5, Replace a Join Table With A Postgres Array

Question

Let's say we have a system that executes 'jobs'. These jobs can be wired up into sequences we call 'integrations' which are effectively an ordered set of jobs.

The classic solution would be a join table:

integrations: id, name
jobs: id, name, commands
integrations_jobs: id, integration_id, job_id, integration_order

where integration_order is the position of that integration_job within the integration.

What if instead we just used a postgres array?

integrations: id, name, [job_id1, job_id2, job_id3]
jobs: id, name, commands

Are there any obvious drawbacks I'm missing with using an array instead of a join table? We are using Rails 5 and Postgres on Heroku.

Answer 1

You can use Postgres array or JSON or enum field but it will affect performance.
Look here

Answer 2

The first drawback is you can not query to find a job in integrations, example:

jobs table
id
1
2

integrations table
id, name, job_ids
1, i1, [1,2]
2, i2, [2]

so, if you want to find integrations of a job which has id 2 , you need to scan integrations table and check if job_ids has value of 2 . If integrations table has a lot of records, it's a big perfomance problem.

If you have a join table, that is just a very simple query and faster. I don't see what wrong if you use a join table.