server/schemahooks.py
author Laure Bourgois <Laure.Bourgois@logilab.fr>
Fri, 27 Feb 2009 17:32:44 +0100
changeset 990 5f1ff5b6907a
parent 0 b97547f5f1fa
child 1138 22f634977c95
child 1251 af40e615dc89
permissions -rw-r--r--
ISiocItem is an interface that is implemented by 'post' entities (in sioc specification) i.e blogentry, mail ... IsiocContainer is an interface that is implemented by 'container' entities (see sioc specification) i.e blog, mailthread ...

"""schema hooks:

- synchronize the living schema object with the persistent schema
- perform physical update on the source when necessary

checking for schema consistency is done in hooks.py

:organization: Logilab
:copyright: 2001-2008 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
"""
__docformat__ = "restructuredtext en"

from yams.schema import BASE_TYPES
from yams.buildobjs import EntityType, RelationType, RelationDefinition
from yams.schema2sql import eschema2sql, rschema2sql, _type_from_constraints

from cubicweb import ValidationError, RepositoryError
from cubicweb.server import schemaserial as ss
from cubicweb.server.pool import Operation, SingleLastOperation, PreCommitOperation
from cubicweb.server.hookhelper import (entity_attr, entity_name,
                                     check_internal_entity)
    
# core entity and relation types which can't be removed
CORE_ETYPES = list(BASE_TYPES) + ['EEType', 'ERType', 'EUser', 'EGroup',
                                  'EConstraint', 'EFRDef', 'ENFRDef']
CORE_RTYPES = ['eid', 'creation_date', 'modification_date',
               'login', 'upassword', 'name',
               'is', 'instanceof', 'owned_by', 'created_by', 'in_group',
               'relation_type', 'from_entity', 'to_entity',
               'constrainted_by',
               'read_permission', 'add_permission',
               'delete_permission', 'updated_permission',
               ]

def get_constraints(session, entity):
    constraints = []
    for cstreid in session.query_data(entity.eid, ()):
        cstrent = session.entity(cstreid)
        cstr = CONSTRAINTS[cstrent.type].deserialize(cstrent.value)
        cstr.eid = cstreid
        constraints.append(cstr)
    return constraints

def add_inline_relation_column(session, etype, rtype):
    """add necessary column and index for an inlined relation"""
    try:
        session.system_sql(str('ALTER TABLE %s ADD COLUMN %s integer'
                               % (etype, rtype)))
        session.info('added column %s to table %s', rtype, etype)
    except:
        # silent exception here, if this error has not been raised because the 
        # column already exists, index creation will fail anyway
        session.exception('error while adding column %s to table %s', etype, rtype)
    # create index before alter table which may expectingly fail during test
    # (sqlite) while index creation should never fail (test for index existence
    # is done by the dbhelper)
    session.pool.source('system').create_index(session, etype, rtype)
    session.info('added index on %s(%s)', etype, rtype)
    session.add_query_data('createdattrs', '%s.%s' % (etype, rtype))


class SchemaOperation(Operation):
    """base class for schema operations"""
    def __init__(self, session, kobj=None, **kwargs):
        self.schema = session.repo.schema
        self.kobj = kobj
        # once Operation.__init__ has been called, event may be triggered, so
        # do this last !
        Operation.__init__(self, session, **kwargs)
        # every schema operation is triggering a schema update
        UpdateSchemaOp(session)
        
class EarlySchemaOperation(SchemaOperation):
    def insert_index(self):
        """schema operation which are inserted at the begining of the queue
        (typically to add/remove entity or relation types)
        """
        i = -1
        for i, op in enumerate(self.session.pending_operations):
            if not isinstance(op, EarlySchemaOperation):
                return i
        return i + 1
    
class UpdateSchemaOp(SingleLastOperation):
    """the update schema operation:

    special operation which should be called once and after all other schema
    operations. It will trigger internal structures rebuilding to consider
    schema changes
    """
    
    def __init__(self, session):
        self.repo = session.repo
        SingleLastOperation.__init__(self, session)
        
    def commit_event(self):
        self.repo.set_schema(self.repo.schema)

        
class DropTableOp(PreCommitOperation):
    """actually remove a database from the application's schema"""
    def precommit_event(self):
        dropped = self.session.query_data('droppedtables',
                                          default=set(), setdefault=True)
        if self.table in dropped:
            return # already processed
        dropped.add(self.table)
        self.session.system_sql('DROP TABLE %s' % self.table)
        self.info('dropped table %s', self.table)
        
class DropColumnOp(PreCommitOperation):
    """actually remove the attribut's column from entity table in the system
    database
    """
    def precommit_event(self):
        session, table, column = self.session, self.table, self.column
        # drop index if any
        session.pool.source('system').drop_index(session, table, column)
        try:
            session.system_sql('ALTER TABLE %s DROP COLUMN %s'
                               % (table, column))
            self.info('dropped column %s from table %s', column, table)
        except Exception, ex:
            # not supported by sqlite for instance
            self.error('error while altering table %s: %s', table, ex)
            

# deletion ####################################################################

class DeleteEETypeOp(SchemaOperation):
    """actually remove the entity type from the application's schema"""    
    def commit_event(self):
        try:
            # del_entity_type also removes entity's relations
            self.schema.del_entity_type(self.kobj)
        except KeyError:
            # s/o entity type have already been deleted
            pass

def before_del_eetype(session, eid):
    """before deleting a EEType entity:
    * check that we don't remove a core entity type
    * cascade to delete related EFRDef and ENFRDef entities
    * instantiate an operation to delete the entity type on commit
    """
    # final entities can't be deleted, don't care about that
    name = check_internal_entity(session, eid, CORE_ETYPES)
    # delete every entities of this type
    session.unsafe_execute('DELETE %s X' % name)
    DropTableOp(session, table=name)
    DeleteEETypeOp(session, name)

def after_del_eetype(session, eid):
    # workflow cleanup
    session.execute('DELETE State X WHERE NOT X state_of Y')
    session.execute('DELETE Transition X WHERE NOT X transition_of Y')

        
class DeleteERTypeOp(SchemaOperation):
    """actually remove the relation type from the application's schema"""    
    def commit_event(self):
        try:
            self.schema.del_relation_type(self.kobj)
        except KeyError:
            # s/o entity type have already been deleted
            pass

def before_del_ertype(session, eid):
    """before deleting a ERType entity:
    * check that we don't remove a core relation type
    * cascade to delete related EFRDef and ENFRDef entities
    * instantiate an operation to delete the relation type on commit
    """
    name = check_internal_entity(session, eid, CORE_RTYPES)
    # delete relation definitions using this relation type
    session.execute('DELETE EFRDef X WHERE X relation_type Y, Y eid %(x)s',
                    {'x': eid})
    session.execute('DELETE ENFRDef X WHERE X relation_type Y, Y eid %(x)s',
                    {'x': eid})
    DeleteERTypeOp(session, name)

    
class DelErdefOp(SchemaOperation):
    """actually remove the relation definition from the application's schema"""
    def commit_event(self):
        subjtype, rtype, objtype = self.kobj
        try:
            self.schema.del_relation_def(subjtype, rtype, objtype)
        except KeyError:
            # relation type may have been already deleted
            pass
        
def after_del_relation_type(session, rdefeid, rtype, rteid):
    """before deleting a EFRDef or ENFRDef entity:
    * if this is a final or inlined relation definition, instantiate an
      operation to drop necessary column, else if this is the last instance
      of a non final relation, instantiate an operation to drop necessary
      table
    * instantiate an operation to delete the relation definition on commit
    * delete the associated relation type when necessary
    """
    subjschema, rschema, objschema = session.repo.schema.schema_by_eid(rdefeid)
    pendings = session.query_data('pendingeids', ())
    # first delete existing relation if necessary
    if rschema.is_final():
        rdeftype = 'EFRDef'
    else:
        rdeftype = 'ENFRDef'
        if not (subjschema.eid in pendings or objschema.eid in pendings):
            session.execute('DELETE X %s Y WHERE X is %s, Y is %s'
                            % (rschema, subjschema, objschema))
    execute = session.unsafe_execute
    rset = execute('Any COUNT(X) WHERE X is %s, X relation_type R,'
                   'R eid %%(x)s' % rdeftype, {'x': rteid})
    lastrel = rset[0][0] == 0
    # we have to update physical schema systematically for final and inlined
    # relations, but only if it's the last instance for this relation type
    # for other relations
    
    if (rschema.is_final() or rschema.inlined):
        rset = execute('Any COUNT(X) WHERE X is %s, X relation_type R, '
                       'R eid %%(x)s, X from_entity E, E name %%(name)s'
                       % rdeftype, {'x': rteid, 'name': str(subjschema)})
        if rset[0][0] == 0 and not subjschema.eid in pendings:
            DropColumnOp(session, table=subjschema.type, column=rschema.type)
    elif lastrel:
        DropTableOp(session, table='%s_relation' % rschema.type)
    # if this is the last instance, drop associated relation type
    if lastrel and not rteid in pendings:
        execute('DELETE ERType X WHERE X eid %(x)s', {'x': rteid}, 'x')
    DelErdefOp(session, (subjschema, rschema, objschema))

        
# addition ####################################################################

class AddEETypeOp(EarlySchemaOperation):
    """actually add the entity type to the application's schema"""    
    def commit_event(self):
        eschema = self.schema.add_entity_type(self.kobj)
        eschema.eid = self.eid
        
def before_add_eetype(session, entity):
    """before adding a EEType entity:
    * check that we are not using an existing entity type,
    """
    name = entity['name']
    schema = session.repo.schema
    if name in schema and schema[name].eid is not None:
        raise RepositoryError('an entity type %s already exists' % name)

def after_add_eetype(session, entity):
    """after adding a EEType entity:
    * create the necessary table
    * set creation_date and modification_date by creating the necessary
      EFRDef entities
    * add owned_by relation by creating the necessary ENFRDef entity
    * register an operation to add the entity type to the application's
      schema on commit
    """
    if entity.get('final'):
        return
    schema = session.repo.schema
    name = entity['name']
    etype = EntityType(name=name, description=entity.get('description'),
                       meta=entity.get('meta')) # don't care about final
    # fake we add it to the schema now to get a correctly initialized schema
    # but remove it before doing anything more dangerous...
    schema = session.repo.schema
    eschema = schema.add_entity_type(etype)
    eschema.set_default_groups()
    # generate table sql and rql to add metadata
    tablesql = eschema2sql(session.pool.source('system').dbhelper, eschema)
    relrqls = []
    for rtype in ('is', 'is_instance_of', 'creation_date', 'modification_date',
                  'created_by', 'owned_by'):
        rschema = schema[rtype]
        sampletype = rschema.subjects()[0]
        desttype = rschema.objects()[0]
        props = rschema.rproperties(sampletype, desttype)
        relrqls += list(ss.rdef2rql(rschema, name, desttype, props))
    # now remove it !
    schema.del_entity_type(name)
    # create the necessary table
    for sql in tablesql.split(';'):
        if sql.strip():
            session.system_sql(sql)
    # register operation to modify the schema on commit
    # this have to be done before adding other relations definitions
    # or permission settings
    AddEETypeOp(session, etype, eid=entity.eid)
    # add meta creation_date, modification_date and owned_by relations
    for rql, kwargs in relrqls:
        session.execute(rql, kwargs)


class AddERTypeOp(EarlySchemaOperation):
    """actually add the relation type to the application's schema"""    
    def commit_event(self):
        rschema = self.schema.add_relation_type(self.kobj)
        rschema.set_default_groups()
        rschema.eid = self.eid
        
def before_add_ertype(session, entity):
    """before adding a ERType entity:
    * check that we are not using an existing relation type,
    * register an operation to add the relation type to the application's
      schema on commit
      
    We don't know yeat this point if a table is necessary
    """
    name = entity['name']
    if name in session.repo.schema.relations():
        raise RepositoryError('a relation type %s already exists' % name)
    
def after_add_ertype(session, entity):
    """after a ERType entity has been added:
    * register an operation to add the relation type to the application's
      schema on commit
    We don't know yeat this point if a table is necessary
    """
    AddERTypeOp(session, RelationType(name=entity['name'],
                                      description=entity.get('description'),
                                      meta=entity.get('meta', False),
                                      inlined=entity.get('inlined', False),
                                      symetric=entity.get('symetric', False)),
                eid=entity.eid)


class AddErdefOp(EarlySchemaOperation):
    """actually add the attribute relation definition to the application's
    schema
    """    
    def commit_event(self):
        self.schema.add_relation_def(self.kobj)

TYPE_CONVERTER = {
    'Boolean': bool,
    'Int': int,
    'Float': float,
    'Password': str,
    'String': unicode,
    'Date' : unicode, 
    'Datetime' : unicode,
    'Time' : unicode,
    }


class AddEFRDefPreCommitOp(PreCommitOperation):
    """an attribute relation (EFRDef) has been added:
    * add the necessary column
    * set default on this column if any and possible
    * register an operation to add the relation definition to the
      application's schema on commit
      
    constraints are handled by specific hooks
    """
    def precommit_event(self):
        session = self.session
        entity = self.entity
        fromentity = entity.from_entity[0]
        relationtype = entity.relation_type[0]
        session.execute('SET X ordernum Y+1 WHERE X from_entity SE, SE eid %(se)s, X ordernum Y, X ordernum >= %(order)s, NOT X eid %(x)s',
                        {'x': entity.eid, 'se': fromentity.eid, 'order': entity.ordernum or 0})
        subj, rtype = str(fromentity.name), str(relationtype.name)
        obj = str(entity.to_entity[0].name)
        # at this point default is a string or None, but we need a correctly
        # typed value
        default = entity.defaultval
        if default is not None:
            default = TYPE_CONVERTER[obj](default)
        constraints = get_constraints(session, entity)
        rdef = RelationDefinition(subj, rtype, obj,
                                  cardinality=entity.cardinality,
                                  order=entity.ordernum,
                                  description=entity.description,
                                  default=default,
                                  indexed=entity.indexed,
                                  fulltextindexed=entity.fulltextindexed,
                                  internationalizable=entity.internationalizable,
                                  constraints=constraints,
                                  eid=entity.eid)
        sysource = session.pool.source('system')
        attrtype = _type_from_constraints(sysource.dbhelper, rdef.object,
                                          constraints)
        # XXX should be moved somehow into lgc.adbh: sqlite doesn't support to
        # add a new column with UNIQUE, it should be added after the ALTER TABLE
        # using ADD INDEX
        if sysource.dbdriver == 'sqlite' and 'UNIQUE' in attrtype:
            extra_unique_index = True
            attrtype = attrtype.replace(' UNIQUE', '')
        else:
            extra_unique_index = False
        # added some str() wrapping query since some backend (eg psycopg) don't
        # allow unicode queries
        try:
            session.system_sql(str('ALTER TABLE %s ADD COLUMN %s %s'
                                   % (subj, rtype, attrtype)))
            self.info('added column %s to table %s', rtype, subj)
        except Exception, ex:
            # the column probably already exists. this occurs when
            # the entity's type has just been added or if the column
            # has not been previously dropped
            self.error('error while altering table %s: %s', subj, ex)
        if extra_unique_index or entity.indexed:
            try:
                sysource.create_index(session, subj, rtype,
                                      unique=extra_unique_index)
            except Exception, ex:
                self.error('error while creating index for %s.%s: %s',
                           subj, rtype, ex)
        # postgres doesn't implement, so do it in two times
        # ALTER TABLE %s ADD COLUMN %s %s SET DEFAULT %s
        if default is not None:
            if isinstance(default, unicode):
                default = default.encode(sysource.encoding)
            try:
                session.system_sql('ALTER TABLE %s ALTER COLUMN %s SET DEFAULT '
                                   '%%(default)s' % (subj, rtype),
                                   {'default': default})
            except Exception, ex:
                # not supported by sqlite for instance
                self.error('error while altering table %s: %s', subj, ex)
            session.system_sql('UPDATE %s SET %s=%%(default)s' % (subj, rtype),
                               {'default': default})
        AddErdefOp(session, rdef)

def after_add_efrdef(session, entity):
    AddEFRDefPreCommitOp(session, entity=entity)


class AddENFRDefPreCommitOp(PreCommitOperation):
    """an actual relation has been added:
    * if this is an inlined relation, add the necessary column
      else if it's the first instance of this relation type, add the
      necessary table and set default permissions
    * register an operation to add the relation definition to the
      application's schema on commit

    constraints are handled by specific hooks
    """
    def precommit_event(self):
        session = self.session
        entity = self.entity
        fromentity = entity.from_entity[0]
        relationtype = entity.relation_type[0] 
        session.execute('SET X ordernum Y+1 WHERE X from_entity SE, SE eid %(se)s, X ordernum Y, X ordernum >= %(order)s, NOT X eid %(x)s',
                        {'x': entity.eid, 'se': fromentity.eid, 'order': entity.ordernum or 0})
        subj, rtype = str(fromentity.name), str(relationtype.name)
        obj = str(entity.to_entity[0].name)
        card = entity.get('cardinality')
        rdef = RelationDefinition(subj, rtype, obj,
                                  cardinality=card,
                                  order=entity.ordernum,
                                  composite=entity.composite,
                                  description=entity.description,
                                  constraints=get_constraints(session, entity),
                                  eid=entity.eid)
        schema = session.repo.schema
        rschema = schema.rschema(rtype)
        # this have to be done before permissions setting
        AddErdefOp(session, rdef)
        if rschema.inlined:
            # need to add a column if the relation is inlined and if this is the
            # first occurence of "Subject relation Something" whatever Something
            # and if it has not been added during other event of the same
            # transaction
            key = '%s.%s' % (subj, rtype)
            try:
                alreadythere = bool(rschema.objects(subj))
            except KeyError:
                alreadythere = False
            if not (alreadythere or
                    key in session.query_data('createdattrs', ())):
                add_inline_relation_column(session, subj, rtype)
        else:
            # need to create the relation if no relation definition in the
            # schema and if it has not been added during other event of the same
            # transaction
            if not (rschema.subjects() or
                    rtype in session.query_data('createdtables', ())):
                try:
                    rschema = schema[rtype]
                    tablesql = rschema2sql(rschema)
                except KeyError:
                    # fake we add it to the schema now to get a correctly
                    # initialized schema but remove it before doing anything
                    # more dangerous...
                    rschema = schema.add_relation_type(rdef)
                    tablesql = rschema2sql(rschema)
                    schema.del_relation_type(rtype)
                # create the necessary table
                for sql in tablesql.split(';'):
                    if sql.strip():
                        self.session.system_sql(sql)
                session.add_query_data('createdtables', rtype)
                
def after_add_enfrdef(session, entity):
    AddENFRDefPreCommitOp(session, entity=entity)


# update ######################################################################

def check_valid_changes(session, entity, ro_attrs=('name', 'final')):
    errors = {}
    # don't use getattr(entity, attr), we would get the modified value if any
    for attr in ro_attrs:
        origval = entity_attr(session, entity.eid, attr)
        if entity.get(attr, origval) != origval:
            errors[attr] = session._("can't change the %s attribute") % \
                           display_name(session, attr)
    if errors:
        raise ValidationError(entity.eid, errors)

def before_update_eetype(session, entity):
    """check name change, handle final"""
    check_valid_changes(session, entity, ro_attrs=('final',))
    # don't use getattr(entity, attr), we would get the modified value if any
    oldname = entity_attr(session, entity.eid, 'name')
    newname = entity.get('name', oldname)
    if newname.lower() != oldname.lower():
        eschema = session.repo.schema[oldname]
        UpdateEntityTypeName(session, eschema=eschema,
                             oldname=oldname, newname=newname)

def before_update_ertype(session, entity):
    """check name change, handle final"""
    check_valid_changes(session, entity)


class UpdateEntityTypeName(SchemaOperation):
    """this operation updates physical storage accordingly"""

    def precommit_event(self):
        # we need sql to operate physical changes on the system database
        sqlexec = self.session.system_sql
        sqlexec('ALTER TABLE %s RENAME TO %s' % (self.oldname, self.newname))
        self.info('renamed table %s to %s', self.oldname, self.newname)
        sqlexec('UPDATE entities SET type=%s WHERE type=%s',
                (self.newname, self.oldname))
        sqlexec('UPDATE deleted_entities SET type=%s WHERE type=%s',
                (self.newname, self.oldname))
        
    def commit_event(self):
        self.session.repo.schema.rename_entity_type(self.oldname, self.newname)


class UpdateRdefOp(SchemaOperation):
    """actually update some properties of a relation definition"""

    def precommit_event(self):
        if 'indexed' in self.values:
            sysource = self.session.pool.source('system')
            table, column = self.kobj[0], self.rschema.type
            if self.values['indexed']:
                sysource.create_index(self.session, table, column)
            else:
                sysource.drop_index(self.session, table, column)
                
    def commit_event(self):
        # structure should be clean, not need to remove entity's relations
        # at this point
        self.rschema._rproperties[self.kobj].update(self.values)
    
def after_update_erdef(session, entity):
    desttype = entity.to_entity[0].name
    rschema = session.repo.schema[entity.relation_type[0].name]
    newvalues = {}
    for prop in rschema.rproperty_defs(desttype):
        if prop == 'constraints':
            continue
        if prop == 'order':
            prop = 'ordernum'
        if prop in entity:
            newvalues[prop] = entity[prop]
    if newvalues:
        subjtype = entity.from_entity[0].name
        UpdateRdefOp(session, (subjtype, desttype), rschema=rschema,
                     values=newvalues)


class UpdateRtypeOp(SchemaOperation):
    """actually update some properties of a relation definition"""    
    def precommit_event(self):
        session = self.session
        rschema = self.rschema
        if rschema.is_final() or not 'inlined' in self.values:
            return # nothing to do
        inlined = self.values['inlined']
        entity = self.entity
        if not entity.inlined_changed(inlined): # check in-lining is necessary/possible
            return # nothing to do
        # inlined changed, make necessary physical changes!
        sqlexec = self.session.system_sql
        rtype = rschema.type
        if not inlined:
            # need to create the relation if it has not been already done by another
            # event of the same transaction
            if not rschema.type in session.query_data('createdtables', ()):
                tablesql = rschema2sql(rschema)
                # create the necessary table
                for sql in tablesql.split(';'):
                    if sql.strip():
                        sqlexec(sql)
                session.add_query_data('createdtables', rschema.type)
            # copy existant data
            for etype in rschema.subjects():
                sqlexec('INSERT INTO %s_relation SELECT eid, %s FROM %s WHERE NOT %s IS NULL'
                        % (rtype, rtype, etype, rtype))
            # drop existant columns
            for etype in rschema.subjects():
                DropColumnOp(session, table=str(etype), column=rtype)
        else:
            for etype in rschema.subjects():
                try:
                    add_inline_relation_column(session, str(etype), rtype)                    
                except Exception, ex:
                    # the column probably already exists. this occurs when
                    # the entity's type has just been added or if the column
                    # has not been previously dropped
                    self.error('error while altering table %s: %s', etype, ex)
                # copy existant data. 
                # XXX don't use, it's not supported by sqlite (at least at when i tried it)
                #sqlexec('UPDATE %(etype)s SET %(rtype)s=eid_to '
                #        'FROM %(rtype)s_relation '
                #        'WHERE %(etype)s.eid=%(rtype)s_relation.eid_from'
                #        % locals())
                cursor = sqlexec('SELECT eid_from, eid_to FROM %(etype)s, '
                                 '%(rtype)s_relation WHERE %(etype)s.eid='
                                 '%(rtype)s_relation.eid_from' % locals())
                args = [{'val': eid_to, 'x': eid} for eid, eid_to in cursor.fetchall()]
                if args:
                    cursor.executemany('UPDATE %s SET %s=%%(val)s WHERE eid=%%(x)s'
                                       % (etype, rtype), args)
                # drop existant table
                DropTableOp(session, table='%s_relation' % rtype)

    def commit_event(self):
        # structure should be clean, not need to remove entity's relations
        # at this point
        self.rschema.__dict__.update(self.values)
    
def after_update_ertype(session, entity):
    rschema = session.repo.schema.rschema(entity.name)
    newvalues = {}
    for prop in ('meta', 'symetric', 'inlined'):
        if prop in entity:
            newvalues[prop] = entity[prop]
    if newvalues:
        UpdateRtypeOp(session, entity=entity, rschema=rschema, values=newvalues)

# constraints synchronization #################################################

from cubicweb.schema import CONSTRAINTS

class ConstraintOp(SchemaOperation):
    """actually update constraint of a relation definition"""
    def prepare_constraints(self, rtype, subjtype, objtype):
        constraints = rtype.rproperty(subjtype, objtype, 'constraints')
        self.constraints = list(constraints)
        rtype.set_rproperty(subjtype, objtype, 'constraints', self.constraints)
        return self.constraints
    
    def precommit_event(self):
        rdef = self.entity.reverse_constrained_by[0]
        session = self.session
        # when the relation is added in the same transaction, the constraint object
        # is created by AddEN?FRDefPreCommitOp, there is nothing to do here
        if rdef.eid in session.query_data('neweids', ()):
            self.cancelled = True
            return 
        self.cancelled = False
        schema = session.repo.schema
        subjtype, rtype, objtype = schema.schema_by_eid(rdef.eid)
        self.prepare_constraints(rtype, subjtype, objtype)
        cstrtype = self.entity.type
        self.cstr = rtype.constraint_by_type(subjtype, objtype, cstrtype)
        self._cstr = CONSTRAINTS[cstrtype].deserialize(self.entity.value)
        self._cstr.eid = self.entity.eid
        # alter the physical schema on size constraint changes
        if self._cstr.type() == 'SizeConstraint' and (
            self.cstr is None or self.cstr.max != self._cstr.max):
            try:
                session.system_sql('ALTER TABLE %s ALTER COLUMN %s TYPE VARCHAR(%s)'
                                   % (subjtype, rtype, self._cstr.max))
                self.info('altered column %s of table %s: now VARCHAR(%s)',
                          rtype, subjtype, self._cstr.max)
            except Exception, ex:
                # not supported by sqlite for instance
                self.error('error while altering table %s: %s', subjtype, ex)
        elif cstrtype == 'UniqueConstraint':
            session.pool.source('system').create_index(
                self.session, str(subjtype), str(rtype), unique=True)
        
    def commit_event(self):
        if self.cancelled:
            return
        # in-place removing
        if not self.cstr is None:
            self.constraints.remove(self.cstr)
        self.constraints.append(self._cstr)

def after_add_econstraint(session, entity):
    ConstraintOp(session, entity=entity)

def after_update_econstraint(session, entity):
    ConstraintOp(session, entity=entity)

class DelConstraintOp(ConstraintOp):
    """actually remove a constraint of a relation definition"""
    
    def precommit_event(self):
        self.prepare_constraints(self.rtype, self.subjtype, self.objtype)
        cstrtype = self.cstr.type()
        # alter the physical schema on size/unique constraint changes
        if cstrtype == 'SizeConstraint':
            try:
                self.session.system_sql('ALTER TABLE %s ALTER COLUMN %s TYPE TEXT'
                                        % (self.subjtype, self.rtype))
                self.info('altered column %s of table %s: now TEXT', 
                          self.rtype,  self.subjtype)
            except Exception, ex:
                # not supported by sqlite for instance
                self.error('error while altering table %s: %s', 
                           self.subjtype, ex)
        elif cstrtype == 'UniqueConstraint':
            self.session.pool.source('system').drop_index(
                self.session, str(self.subjtype), str(self.rtype), unique=True)
                
    def commit_event(self):
        self.constraints.remove(self.cstr)


def before_delete_constrained_by(session, fromeid, rtype, toeid):
    if not fromeid in session.query_data('pendingeids', ()):
        schema = session.repo.schema
        entity = session.eid_rset(toeid).get_entity(0, 0)
        subjtype, rtype, objtype = schema.schema_by_eid(fromeid)
        try:
            cstr = rtype.constraint_by_type(subjtype, objtype, entity.cstrtype[0].name)
            DelConstraintOp(session, subjtype=subjtype, rtype=rtype, objtype=objtype,
                            cstr=cstr)
        except IndexError:
            session.critical('constraint type no more accessible')


def after_add_constrained_by(session, fromeid, rtype, toeid):
    if fromeid in session.query_data('neweids', ()):
        session.add_query_data(fromeid, toeid)

    
# schema permissions synchronization ##########################################

class PermissionOp(Operation):
    """base class to synchronize schema permission definitions"""
    def __init__(self, session, perm, etype_eid):
        self.perm = perm
        try:
            self.name = entity_name(session, etype_eid)
        except IndexError:
            self.error('changing permission of a no more existant type #%s',
                etype_eid)
        else:
            Operation.__init__(self, session)

class AddGroupPermissionOp(PermissionOp):
    """synchronize schema when a *_permission relation has been added on a group
    """
    def __init__(self, session, perm, etype_eid, group_eid):
        self.group = entity_name(session, group_eid)
        PermissionOp.__init__(self, session, perm, etype_eid)
        
    def commit_event(self):
        """the observed connections pool has been commited"""
        try:
            erschema = self.schema[self.name]
        except KeyError:
            # duh, schema not found, log error and skip operation
            self.error('no schema for %s', self.name)
            return
        groups = list(erschema.get_groups(self.perm))
        try:            
            groups.index(self.group)
            self.warning('group %s already have permission %s on %s',
                         self.group, self.perm, erschema.type)
        except ValueError:
            groups.append(self.group)
            erschema.set_groups(self.perm, groups)

class AddRQLExpressionPermissionOp(PermissionOp):
    """synchronize schema when a *_permission relation has been added on a rql
    expression
    """
    def __init__(self, session, perm, etype_eid, expression):
        self.expr = expression
        PermissionOp.__init__(self, session, perm, etype_eid)
        
    def commit_event(self):
        """the observed connections pool has been commited"""
        try:
            erschema = self.schema[self.name]
        except KeyError:
            # duh, schema not found, log error and skip operation
            self.error('no schema for %s', self.name)
            return
        exprs = list(erschema.get_rqlexprs(self.perm))
        exprs.append(erschema.rql_expression(self.expr))
        erschema.set_rqlexprs(self.perm, exprs)

def after_add_permission(session, subject, rtype, object):
    """added entity/relation *_permission, need to update schema"""
    perm = rtype.split('_', 1)[0]
    if session.describe(object)[0] == 'EGroup':
        AddGroupPermissionOp(session, perm, subject, object)
    else: # RQLExpression
        expr = session.execute('Any EXPR WHERE X eid %(x)s, X expression EXPR',
                               {'x': object}, 'x')[0][0]
        AddRQLExpressionPermissionOp(session, perm, subject, expr)
    

        
class DelGroupPermissionOp(AddGroupPermissionOp):
    """synchronize schema when a *_permission relation has been deleted from a group"""
        
    def commit_event(self):
        """the observed connections pool has been commited"""
        try:
            erschema = self.schema[self.name]
        except KeyError:
            # duh, schema not found, log error and skip operation
            self.error('no schema for %s', self.name)
            return
        groups = list(erschema.get_groups(self.perm))
        try:            
            groups.remove(self.group)
            erschema.set_groups(self.perm, groups)
        except ValueError:
            self.error('can\'t remove permission %s on %s to group %s',
                self.perm, erschema.type, self.group)

        
class DelRQLExpressionPermissionOp(AddRQLExpressionPermissionOp):
    """synchronize schema when a *_permission relation has been deleted from an rql expression"""
        
    def commit_event(self):
        """the observed connections pool has been commited"""
        try:
            erschema = self.schema[self.name]
        except KeyError:
            # duh, schema not found, log error and skip operation
            self.error('no schema for %s', self.name)
            return
        rqlexprs = list(erschema.get_rqlexprs(self.perm))
        for i, rqlexpr in enumerate(rqlexprs):
            if rqlexpr.expression == self.expr:
                rqlexprs.pop(i)
                break
        else:
            self.error('can\'t remove permission %s on %s for expression %s',
                self.perm, erschema.type, self.expr)
            return
        erschema.set_rqlexprs(self.perm, rqlexprs)

                
def before_del_permission(session, subject, rtype, object):
    """delete entity/relation *_permission, need to update schema

    skip the operation if the related type is being deleted
    """
    if subject in session.query_data('pendingeids', ()):
        return
    perm = rtype.split('_', 1)[0]
    if session.describe(object)[0] == 'EGroup':
        DelGroupPermissionOp(session, perm, subject, object)
    else: # RQLExpression
        expr = session.execute('Any EXPR WHERE X eid %(x)s, X expression EXPR',
                               {'x': object}, 'x')[0][0]
        DelRQLExpressionPermissionOp(session, perm, subject, expr)


def rebuild_infered_relations(session, subject, rtype, object):
    # registering a schema operation will trigger a call to
    # repo.set_schema() on commit which will in turn rebuild
    # infered relation definitions
    UpdateSchemaOp(session)


def _register_schema_hooks(hm):
    """register schema related hooks on the hooks manager"""
    # schema synchronisation #####################
    # before/after add
    hm.register_hook(before_add_eetype, 'before_add_entity', 'EEType')
    hm.register_hook(before_add_ertype, 'before_add_entity', 'ERType')
    hm.register_hook(after_add_eetype, 'after_add_entity', 'EEType')
    hm.register_hook(after_add_ertype, 'after_add_entity', 'ERType')
    hm.register_hook(after_add_efrdef, 'after_add_entity', 'EFRDef')
    hm.register_hook(after_add_enfrdef, 'after_add_entity', 'ENFRDef')
    # before/after update
    hm.register_hook(before_update_eetype, 'before_update_entity', 'EEType')
    hm.register_hook(before_update_ertype, 'before_update_entity', 'ERType')
    hm.register_hook(after_update_ertype, 'after_update_entity', 'ERType')
    hm.register_hook(after_update_erdef, 'after_update_entity', 'EFRDef')
    hm.register_hook(after_update_erdef, 'after_update_entity', 'ENFRDef')
    # before/after delete
    hm.register_hook(before_del_eetype, 'before_delete_entity', 'EEType')
    hm.register_hook(after_del_eetype, 'after_delete_entity', 'EEType')
    hm.register_hook(before_del_ertype, 'before_delete_entity', 'ERType')
    hm.register_hook(after_del_relation_type, 'after_delete_relation', 'relation_type')
    hm.register_hook(rebuild_infered_relations, 'after_add_relation', 'specializes')
    hm.register_hook(rebuild_infered_relations, 'after_delete_relation', 'specializes')    
    # constraints synchronization hooks
    hm.register_hook(after_add_econstraint, 'after_add_entity', 'EConstraint')
    hm.register_hook(after_update_econstraint, 'after_update_entity', 'EConstraint')
    hm.register_hook(before_delete_constrained_by, 'before_delete_relation', 'constrained_by')
    hm.register_hook(after_add_constrained_by, 'after_add_relation', 'constrained_by')
    # permissions synchronisation ################
    for perm in ('read_permission', 'add_permission',
                 'delete_permission', 'update_permission'):
        hm.register_hook(after_add_permission, 'after_add_relation', perm)
        hm.register_hook(before_del_permission, 'before_delete_relation', perm)