Execute code at update or install

Information found here:

• https://www.odoo.com/fr_FR/forum/help-1/question/how-can-i-execute-a-sql-statement-on-module-update-and-installation-6131
• http://www.mindissoftware.com/2014/11/22/Odoo-Load-Addons-And-Modules/

The init function will only be called at addon update or install! See most reports e.g.: addons/account/report/account_report:

class report_account_receivable(osv.osv):
    _name = "report.account.receivable"
    _description = "Receivable accounts"
    _auto = False
    _columns = {
        'name': fields.char('Week of Year', size=7, readonly=True),
        'type': fields.selection(_code_get, 'Account Type', required=True),
        'balance':fields.float('Balance', readonly=True),
        'debit':fields.float('Debit', readonly=True),
        'credit':fields.float('Credit', readonly=True),
    }
    _order = 'name desc'

    def init(self, cr):
        tools.drop_view_if_exists(cr, 'report_account_receivable')
        cr.execute("""
            create or replace view report_account_receivable as (
                select
                    min(l.id) as id,
                    to_char(date,'YYYY:IW') as name,
                    sum(l.debit-l.credit) as balance,
                    sum(l.debit) as debit,
                    sum(l.credit) as credit,
                    a.type
                from
                    account_move_line l
                left join
                    account_account a on (l.account_id=a.id)
                where
                    l.state <> 'draft'
                group by
                    to_char(date,'YYYY:IW'), a.type
            )""")