Querying an Odoo many-to-many field using raw SQL - sql

Question

I want to display many-to-many field in report.
Currently my model is as follows:
from openerp.esv import orm, fields
class myClass(orm.Model):
_name = 'my.Class'
_columns = {
'teacher_id': fields.many2many('fci.staff','lgna_teacher','ids_lol',
'teacher_ids','Observers'),
}
And I want to display them using SQL select statement.

Answer 1

In my example below, I'm considering that teachers and courses have a many-to-many relationship: teachers can teach multiple courses and courses can be taught by multiple teachers.
from openerp.osv import orm, fields
class Teachers(orm.Model):
_name = 'teachers'
name = fields.Char()
class Course(rm.Model):
_name = 'course'
title = fields.Char()
teacher_ids = fields.Many2many('teachers', 'teacher_course_rel', 'course_id',
'teacher_id', string='Teachers')
Using SQL (either using Odoo API or your DBMS), you can query the junction table (or cross-reference table) teacher_course_rel to retrieve the needed columns from each table.
For instance, the query below retrieves all the teachers' names teaching the Physics course:
SELECT c.title, t.name
FROM teacher AS t
INNER JOIN teacher_course_rel AS tcr
ON t.id = tcr.teacher_id
INNER JOIN course AS c
ON tcr.course_id = c.id
WHERE c.title = 'Physics'
Please note that I have used an SQL INNER JOIN which returns rows from the two tables only when the conditions are met (i.e. the two INNER JOIN conditions and the WHERE condition). For your purposes, you may wish to use a different type of join depending on the information you wish to retrieve from both your tables.