Recipes/RecordOwner: record_owner.py

"""
A plugin for Elixir, which adds and maintains columns for the user that creates, 
and respectivelly updates, a record.

The user may be supplied directly, or a function getting an argument to fetch 
the user may be supplied. the argument (getter_param) is optional, defaulting 
to None.

The field names may be optionally supplied in the column_field_names parameter.
If column_field_names is None (by default), ['created_by', 'updated_by'], 
will be assumed. The field names may be already defined, in which case they will 
be used as they are. This feature will allow those fields belonging to entity 
relationships. If only one field will be supplied, the same field name will be 
set for inserter and updater, the effect will be to keep the last toucher. In 
combination with the versioned extension, the inserter will be the user who 
touched version 1.

Example:

def get_current_user(param):
    return current_user

class Movie(Entity):
    title = Field(Unicode(30))
    year = Field(Integer)
    acts_as_owned(Unicode(17), get_current_user, 12, ['toucher'])


This extension may well be complemented by the excellent 'versioned' extension. 
"""

from sqlalchemy            import Column, and_
from sqlalchemy.orm        import mapper, MapperExtension, EXT_CONTINUE

from elixir.statements     import Statement
from elixir.properties     import EntityBuilder

__all__ = ['acts_as_owned']
__doc_all__ = []

#
# utility functions
#

def get_entity_where(instance):
    clauses = []
    for column in instance.table.primary_key.columns:
        instance_value = getattr(instance, column.name)
        clauses.append(column==instance_value)
    return and_(*clauses)

def get_current_user(instance):
    gcu = instance.__class__.__get_current_user__
    if callable(gcu):
        return gcu(instance.__getter_param__)
    else:
        return gcu

#
# a mapper extension to track the user that insert, or update a record
#

class OwnedMapperExtension(MapperExtension):
    
    def before_insert(self, mapper, connection, instance):
        owned_columns = instance.__class__.__owned_column_field_names__
        setattr(instance, owned_columns[1], None)
        setattr(instance, owned_columns[0], get_current_user(instance))
        return EXT_CONTINUE
        
    def before_update(self, mapper, connection, instance):
        owned_columns = instance.__class__.__owned_column_field_names__
        setattr(instance, owned_columns[1], get_current_user(instance))
        return EXT_CONTINUE

owned_mapper_extension = OwnedMapperExtension()


#
# the acts_as_owned statement
#

class OwnedEntityBuilder(EntityBuilder):
    
    def __init__(self, entity, column_type, get_current_user, getter_param=None, 
                 column_field_names=None):
        entity._descriptor.add_mapper_extension(owned_mapper_extension)
        self.entity = entity
        self.add_mapper_extension(owned_mapper_extension)

        entity.__current_user_column_type__ = column_type
        if column_field_names in [None, []]:
            column_field_names = ['created_by', 'updated_by']
        entity.__owned_column_field_names__ = column_field_names
        if len(column_field_names) < 2:
            entity.__owned_column_field_names__.append(column_field_names[0])
        if callable(get_current_user):
            entity.__get_current_user__ = staticmethod(get_current_user)
            entity.__getter_param__ = getter_param
        else: entity.__get_current_user__ = get_current_user
        
    def create_non_pk_cols(self):
        # add columns for the user who inserted or updated the record, if fields
        # don't exist yet. this to allow their definition as relationships etc.
        for fieldname in self.entity.__owned_column_field_names__:
            if fieldname not in \
                    [col.name for col in self.entity._descriptor.columns]:
                self.entity._descriptor.add_column(Column(fieldname, 
                                    self.entity.__current_user_column_type__))

acts_as_owned = Statement(OwnedEntityBuilder)