Fields Introduction on Openerp

Here’s the header of the initialization method of the class any field defined in OpenERP inherits (as you can see in server/bin/osv/fields.py):

def __init__(self, string='unknown', required=False, readonly=False,
             domain=None, context="", states=None, priority=0, change_default=False, size=None,
             ondelete="set null", translate=False, select=False, **args) :

There are a common set of optional parameters that are available to most field types:

change_default:	Whether or not the user can define default values on other fields depending on the value of this field. Those default values need to be defined in the ir.values table.
help:	A description of how the field should be used: longer and more descriptive than string. It will appear in a tooltip when the mouse hovers over the field.
ondelete:	How to handle deletions in a related record. Allowable values are: ‘restrict’, ‘no action’, ‘cascade’, ‘set null’, and ‘set default’.
priority:	Not used?
readonly:	True if the user cannot edit this field, otherwise False.
required:	True if this field must have a value before the object can be saved, otherwise False.
size:	The size of the field in the database: number characters or digits.
states:	Lets you override other parameters for specific states of this object. Accepts a dictionary with the state names as keys and a list of name/value tuples as the values. For example: states={‘posted’:[(‘readonly’,True)]}
string:	The field name as it should appear in a label or column header. Strings containing non-ASCII characters must use python unicode objects. For example: ‘tested’: fields.boolean(u’Testé’)
translate:	True if the content of this field should be translated, otherwise False.

                            There are also some optional parameters that are specific to some field types:

context:	Define a variable’s value visible in the view’s context or an on-change function. Used when searching child table of one2many relationship?
domain:	Domain restriction on a relational field. Default value: []. Example: domain=[(‘field’,’=’,value)])
invisible:	Hide the field’s value in forms. For example, a password.
on_change:	Default value for the on_change attribute in the view. This will launch a function on the server when the field changes in the client. For example, on_change=”onchange_shop_id(shop_id)”.
relation:	Used when a field is an id reference to another table. This is the name of the table to look in. Most commonly used with related and function field types.
select:	Default value for the select attribute in the view. 1 means basic search, and 2 means advanced search.