Project a single column of a table filtered by tag from act as taggale

Currently the only way I know to sub select in rails is with arel,
for exmaple -

sub = x.where(y:'x').project(:id)
select = a.where(a[:x_id].in(sub))


question is,
if x is using the acts as taggable on gem and need to filtered by a specific tag, use with tagged_with method.

tagged_with

How can I still achive same database efficiency, it looks like the tagged with method override the projection.

tagged with

thanks,

1 Answer
1

You don't need Arel to build sub selects in Rails:

sub = X.where(y: 'x')
select = A.where(x_id: sub)


generates the following SQL, assuming A's table name is as and X's is xs:

as

xs

SELECT "as".* FROM "as" WHERE "as"."x_id" IN (SELECT "xs"."id" FROM "xs" WHERE "xs"."y" = 'x')


Testing with tagged_with worked: A.where(x_id: X.tagged_with('my_tag')) generates the expected SQL, at least for Rails 5.1, version on which I've tested.

tagged_with

A.where(x_id: X.tagged_with('my_tag'))

Edit

You can specify the column used inside the subselect if needed. If you don't specify it, the primary key column is the default:

sub = X.where(y: 'x').select(:x_y_id)
select = A.where(x_id: sub)


will generate the following SQL:

SELECT "as".* FROM "as" WHERE "as"."x_id" IN (SELECT "xs"."x_y_id" FROM "xs" WHERE "xs"."y" = 'x')


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