How to create a relation fields in odoo?

Question

There are no proper examples on how to create relational fields in openerp like one2many, many2many, many2one and one2one. So can anyone show me with example on sales module.

Answer 1

Might helps you,

_columns = {
'current_rate': fields.related('company_currency_id','rate_silent', type='float', relation='res.currency',digits_compute=dp.get_precision( 'Account'), string='Current Rate', readonly=True),
}

Here,

company_currency_id => the field in the same model through which the new field will be relate,

rate_silent => is the field which you are going to relate with new field, means the field from source model,

relation => is the source model name,

type => is the datatype of the source field

Note : When you update value in your newly defined related field it will be updated in source field as well, though it's always advisable to set readonly in newly defined field.

Answer 2

I don't have particular example of sales module. But you can get the general idea from below syntax.It would be helpful for any kind of application.

class openerp.fields.Many2one(comodel_name=None, string=None, **kwargs)

Bases: openerp.fields._Relational

The value of such a field is a recordset of size 0 (no record) or 1 (a single record). Parameters

comodel_name -- name of the target model (string)
domain -- an optional domain to set on candidate values on the client side (domain or string)
context -- an optional context to use on the client side when handling that field (dictionary)
ondelete -- what to do when the referred record is deleted; possible values are: 'set null', 'restrict', 'cascade'
auto_join -- whether JOINs are generated upon search through that field (boolean, by default False)
delegate -- set it to True to make fields of the target model accessible from the current model (corresponds to _inherits)

The attribute comodel_name is mandatory except in the case of related fields or field extensions.

=======================================================================

class openerp.fields.One2many(comodel_name=None, inverse_name=None, string=None, **kwargs)

Bases: openerp.fields._RelationalMulti

One2many field; the value of such a field is the recordset of all the records in comodel_name such that the field inverse_name is equal to the current record.

Parameters  
comodel_name -- name of the target model (string)
inverse_name -- name of the inverse Many2one field in comodel_name     (string)
domain -- an optional domain to set on candidate values on the client  side (domain or string)
context -- an optional context to use on the client side when handling that field (dictionary)
auto_join -- whether JOINs are generated upon search through that  field (boolean, by default False)
limit -- optional limit to use upon read (integer)

The attributes comodel_name and inverse_name are mandatory except in the case of related fields or field extensions.

==========================================================================

class openerp.fields.Many2many(comodel_name=None, relation=None, column1=None, column2=None, string=None, **kwargs)

Bases: openerp.fields._RelationalMulti

Many2many field; the value of such a field is the recordset.

Parameters----------------------------------------------------------------

comodel_name -- name of the target model (string)

The attribute comodel_name is mandatory except in the case of related fields or field extensions.

Parameters

relation -- optional name of the table that stores the relation in the database (string)
column1 -- optional name of the column referring to "these" records in the table relation (string)
column2 -- optional name of the column referring to "those" records in the table relation (string)
The attributes relation, column1 and column2 are optional. If not given, names are automatically generated from model names, provided model_name and comodel_name are different!

Parameters

domain -- an optional domain to set on candidate values on the client side (domain or string)
context -- an optional context to use on the client side when handling that field (dictionary)
limit -- optional limit to use upon read (integer)