How to use find_by_sql properly? - ruby-on-rails

Question

I have the following model
class Backup < ActiveRecord::Base
belongs_to :component
belongs_to :backup_medium
def self.search(value)
join_tables = "backups, components, backup_media"
joins = "backups.backup_medium_id = backup_media.id and components.id = backups.component_id"
c = Backup.find_by_sql "select * from #{join_tables} where components.name like '%#{value}%' and #{joins}"
b = Backup.find_by_sql "select * from #{join_tables} where backup_media.name like '%#{value}%' and #{joins}"
c.count > 0 ? c : b
end
end
In pry, when I run Backup.all.class, I get
=> Backup::ActiveRecord_Relation
but when I run Backup.search('xxx').class, I get
=> Array
Since the search should return a subset of all, I think I need to return an Active Record_Relation. What am I missing?

Answer 1

From the documentation:
Executes a custom SQL query against your database and returns all the
results. The results will be returned as an array with columns
requested encapsulated as attributes of the model you call this method
from. If you call Product.find_by_sql then the results will be
returned in a Product object with the attributes you specified in the
SQL query.
So you will get an array of Backup instances.
Note that you probably should not do it this way. Using string interpolation in a query opens you up to SQL injection attacks and gains you nothing. Also, you can get quite a bit more flexibility using ActiveRecord scopes for this.
def self.my_includes
includes(:components, :backup_media)
end
def self.by_component_name(name)
media_includes.where("components.name like ?", "'%#{name}%'")
end
def self.by_media_name(name)
media_includes.where("backup_media.name like ?", "'%#{value}%'")
end
def self.search(name)
by_component(name).any? ? by_component_name : by_media_name
end
You can then call
Backup.search(name)
as well as
Backup.by_component_name(name)
or
Backup.by_media_name(name)

Answer 2

find_by_sql returns an array of objects, not a Relation. If you want to return relation for consistency try to rewrite your search to use ActiveRecord api:
def self.search(value)
query = Backup.includes(:component, :backup_medium)
by_component_name = query.where("components.name like ?", "'%#{value}%'")
by_media_name = query.where("backup_media.name like ?", "'%#{value}%'")
by_component_name.any? ? by_component_name : by_media_name
end
or, if you still want to use sql, you can try to fetch record ids and then make a second query:
def self.search(value)
# ...
c = Backup.find_by_sql "select id from #{join_tables} where components.name like '%#{value}%' and #{joins}"
b = Backup.find_by_sql "select id from #{join_tables} where backup_media.name like '%#{value}%' and #{joins}"
ids = c.count > 0 ? c : b
Backup.where(id: ids)
end

Answer 3

So I am unable to get the syntax right for the media_includes, but inspired by your solution I have succeeded by using joins.
I created a small demo project which just shows the code related to search. You can take a look at https://github.com/pamh09/rails-search-demo. If you want to collaborate on a solution, I think this would be more efficient than trying to paste all the code here. That said, I do have a working solution if you'd rather not bother. But I would like to see what the right syntax is.
Below is the model code. It's very possible that I just have some kind of syntactic mismatch since I am not very familiar with how rails does its database magic (obviously).
class Backup < ApplicationRecord
belongs_to :component
belongs_to :backup_medium
#---- code below does not work ---
# in pry
# pry(Backup):1> by_media('bak').any?
# (0.0ms) SELECT COUNT(*) FROM "backups" WHERE (backup_media = 'bak')
# ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: backup_media.name: SELECT COUNT(*) FROM "backups" WHERE (backup_media.name = 'bak')
def self.my_includes
includes(:component, :backup_medium)
end
def self.by_component(name)
my_includes.where("components.name = ?", name)
end
def self.by_media(name)
my_includes.where("backup_media.name = ?", name)
end
def self.search_by(name)
by_component(name).any? ? by_component_name : by_media_name
end
# ----- code below works ... call search('string') -----
# I was unable to get the like query to work without using #{name}
def self.by_component_like(name)
# Note: joins (singular).where (plural.column ...)
joins(:component).where("components.name like '%#{name}%'")
end
def self.by_media_like(name)
joins(:backup_medium).where("backup_media.name like '%#{name}%'")
end
def self.search(name)
by_component_like(name).any? ? by_component_like(name) : by_media_like(name)
end
end
And, as noted in the code. I could not figure you how to use the ? with LIKE as the query would come in as LIKE '%'xxx'%' instead of '%xxx%'.