Run mysql query from a controller in ruby on rails - mysql

Question

I need run a mysql query from the controller but I do not know how to connect to db.
this is my method:
def set_dcs
sql="select employees.nombre, employees.apellido_paterno, employees.apellido_materno from employees, activities, field_tests
where activities.field_test_id=field_tests.id and employees.id=activities.dcs_id and field_tests.id=id"
end
How do I get the result of the query?
How could I do the same query but with the ActiveRecord?

Answer 1

You can execute raw SQL through ActiveRecord::Base.connection but I rarely recommend it and certainly not in this case, but for edification purposes
def set_dcs
sql= <<SQL
select employees.nombre, employees.apellido_paterno, employees.apellido_materno
from employees, activities, field_tests
where activities.field_test_id=field_tests.id and employees.id=activities.dcs_id and field_tests.id=id
SQL
ActiveRecord::Base.connection.exec_query(sql)
end
I was not sure what the trailing id is in reference to and it will raise a SQL error due to it's ambiguity. I am going to assume it is a parameter and the primary search condition where as the rest are table joins.
That being said since you are using rails these can be true associations and joins resulting in far more readable controller code e.g. Model Definitions
class Employee < ActiveRecord::Base
has_many :activities, foreign_key: :dcs_id
has_many :field_tests, through: :activities
end
class FieldTest < ActiveRecord::Base
has_many :activities
end
class Activity < ActiveRecord::Base
belongs_to :employee, foreign_key: :dcs_id
belongs_to :field_test
end
Then the controller is simply
Employee.
select("employees.nombre, employees.apellido_paterno, employees.apellido_materno").
joins(:field_tests).where(field_tests: {id: SOME_ID})
the resulting SQL will be similar to
SELECT
employees.nombre,
employees.apellido_paterno,
employees.apellido_materno
FROM
employees
INNER JOIN activities ON employees.id = activities.dcs_id
INNER JOIN field_tests ON activities.field_test_id = field_tests.id
WHERE
field_tests.id = SOME_ID
And this will return a collection of Employee Objects rather than an ActiveRecord::Result (returned from ActiveRecord::Base.connection.exec_query) which is more similar to an Array than anything else.