Rails ActiveRecord Join Confusion

Question

In the console this code:

Patient.joins(:notes,:recordings).find(1)

Returns

ActiveRecord::RecordNotFound: Couldn't find Patient with id=1

Which is bizarre because in the same console Patient.find(1) works without any issue and retrieves the record of the patient with id 1.

My understanding is that I should be able to do:

a = Patient.joins(:notes,:recordings).find(1)
a.notes
a.recordings

And a.notes should return all the notes associated with the patient with id 1 and same for a.recordings. It's clear I'm missing something here...any ideas?

score 2 · Accepted Answer · answered Feb 06 '14 at 21:16

2

That's because rails does INNER JOIN by default. your patient 1 doesn't have either notes or recordings

If can do a left join instead.

Patient.joins("LEFT JOIN notes on notes.patient_id = patients.id")
       .joins("LEFT JOIN recordings on recordings.patient_id = patients.id")
       .find(1)

or load the patient and then load the associations

 a = Patient.find(1)
 a.notes
 a.recordings

answered Feb 06 '14 at 21:16

usha

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change find(1) to `first` ? – Phlip Feb 06 '14 at 21:23
When the id doesn't exist is there a way to make it return an empty association rather than throw an error? – Morgan Feb 06 '14 at 21:40
1

A better solution would be Patient.includes(:notes, :recordings).find(1) – Coenwulf Feb 21 '14 at 19:02

score 1 · Answer 2 · edited May 23 '17 at 10:25

1

You may be interested in include type functionality (for eager loading). See: Rails :include vs. :joins

edited May 23 '17 at 10:25

Community

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1

answered Feb 06 '14 at 22:08

Coenwulf

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Rails ActiveRecord Join Confusion

2 Answers2