In OpenERP we can create many2one and one2many relationships between models very easily by creating many2one and one2many fields. You just need to declare a field in _columns and then using this field normally in the rest programming and views as we normally do.

I created a small module to explain called hospital, I have two objects patient and doctor. To establish relationship between these two entities or objects, create doctor_id field in patient model as many2one, and patient_id as one2many in doctor model.

The relationship can be explained as one doctor with many patients and many patients going to a single doctor.

Now create a many2one field as:

in class patient(osv.osv):

'doctor_id':fields.many2one('doctor','Doctor'),

and in class doctor(osv.osv):

'patient_id':fields.one2many('patient','doctor_id',),

Basic syntax for declaring a many2one field:

fields.many2one(
        'object.name',
        'field name',
        optional parameters)

where first parameter is the model to which the relation is to be created, and field name is the name for the field.

declaring a one2many field:

fields.one2many(
        'other.object.name',
        'Field relation id',
        'Fieldname',
        optional parameter)

Optional parameters:

1. required = true/false: means a mandatory field,
2. readonly = true/flase: means not editable field,
3. invisible = true/false: to be visible in the view or not, 4 states: these can be defined as you wish,.