To Write Multiple Conditions LEFT JOIN in Rails

ModelA
  - id
  - c_id
  - d_id

ModelB
  - id
  - name
  - c_id
  - d_id

Shared columns for ModelA and ModelB are c_id and d_id.

SELECT 
  A.id, B.name
from
  ModelA ASA
  LEFT JOIN ModelB ASB
    ON A.c_id = B.c_id AND A.d_id = B.d_id

How do I retrieve data like this with Rails (ActiveRecord)?

ruby-on-rails mysql sql rails-activerecord

2022-09-30 17:35

1 Answers

Use joins to write as follows:

ModelA.joins(%{
  LEFT JOIN model_bs
  ON model_a.c_id = model_b.c_id AND model_a.d_id = model_b.d_id
}).select("*,model_b.name ASb_name") .map {|a|a.b_name}

where model_a, model_b is the table name.The record you get is an instance of ModelA, but name can be obtained through the singular method name.

If you specify a compound key in the ON clause, there is no other way but to write SQL (part of ) directly.Probably.

2022-09-30 17:35

If you have any answers or tips

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