Inner Join in Rails options_from_collection_for_select - ruby-on-rails

Question

I have created below join query to fetch group name details.I am using below query in postgresql.
select DISTINCT e.group_id,e.groupname from user_group_table u, execution_groups e where (u.user_id=e.user_id or u.group_id=e.group_id) and u.user_id=12;
How to write above join query using "options_from_collection_for_select" in rails?
I have tried below code
user_groups = UserGroupTable.where(:user_id => id)
#execution_group_options = ExecutionGroup.where(user_id: user_groups.select(:user_id)).or(ExecutionGroup.where(group_id: user_groups.select(:group_id)))
Getting below error
SELECT "execution_groups".* FROM "execution_groups" WHERE "execution_groups"."user_id" IN (SELECT "user_group_table"."user_id" FROM "user_group_table" WHERE "user_group_table"."user_id" = ?) [["user_id", 6]]
"Threw an exception inside test.new() undefined method `or' for #<ExecutionGroup::ActiveRecord_Relation:0x00007faf9e10ee38>"
Threw an exception inside test.new() undefined method `or' for #<ExecutionGroup::ActiveRecord_Relation:0x00007faf9e10ee38>

Answer 1

Let's start of by writing that query in the Rails query syntax.
I'll assume that user_group_table is available through the UserGroup model and execution_groups is available through the ExecutionGroup model.
# in controller
user_groups = UserGroup.where(user_id: 12)
#execution_group_options =
ExecutionGroup.where(user_id: user_groups.select(:user_id))
.or(ExecutionGroup.where(group_id: user_groups.select(:group_id)))
This produces the following SQL:
SELECT execution_groups.*
FROM execution_groups
WHERE
execution_groups.user_id IN (
SELECT user_group_table.user_id
FROM user_group_table
WHERE user_group_table.user_id = 12
)
OR
execution_groups.group_id IN (
SELECT user_group_table.group_id
FROM user_group_table
WHERE user_group_table.user_id = 12
)
Which should produce the same collection (assuming there are no ExecutionGroup records that have the same group_id and groupname).
With the above in place you can use the following in your view:
options_from_collection_for_select(#execution_group_options, 'group_id', 'groupname')
If there are ExecutionGroup records with both the same group_id and groupname. You can instead use:
options_for_select(#execution_group_options.distinct.pluck(:groupname, :group_id))
If you don't have access to or (introduced in Ruby on Rails 5), things become slightly more complicated. You should be able to use the internal arel interface.
# in controller
user_groups = UserGroup.where(user_id: 12)
exec_groups_table = ExecutionGroup.arel_table
#execution_group_options = ExecutionGroup.where(
exec_groups_table[:user_id].in(user_groups.select(:user_id).arel)
.or(exec_groups_table[:group_id].in(user_groups.select(:group_id).arel))
)
This should produce the exact same query. Other than the controller code nothing changes.