Many2one : Store a relation against a co-model:

arel_id = fields.Many2one('res.users')

arel_id = fields.Many2one(comodel_name='res.users')

an_other_rel_id = fields.Many2one(comodel_name='res.partner', delegate=True)

Specific options:

comodel_name: name of the opposite model

delegate: set it to True to make fields of the target model accessible from the current model (corresponds to _inherits)

One2many : Store a relation against many rows of co-model:

arel_ids = fields.One2many('res.users', 'rel_id')

arel_ids = fields.One2many(comodel_name='res.users', inverse_name='rel_id')

Specific options:

comodel_name: name of the opposite model

inverse_name: relational column of the opposite model

Many2many : Store a relation against many2many rows of co-model:

arel_ids = fields.Many2many('res.users')

arel_ids = fields.Many2many(comodel_name='res.users', relation='table_name', column1='col_name', column2='other_col_name')

Specific options:

comodel_name: name of the opposite model

relation: relational table name

columns1: relational table left column name

columns2: relational table right column name