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"""
Code to generate a Python model from a database or differences
between a model and database.
Some of this is borrowed heavily from the AutoCode project at:
http://code.google.com/p/sqlautocode/
"""
import sys
import logging
import sqlalchemy
import migrate
import migrate.changeset
log = logging.getLogger(__name__)
HEADER = """
## File autogenerated by genmodel.py
from sqlalchemy import *
meta = MetaData()
"""
DECLARATIVE_HEADER = """
## File autogenerated by genmodel.py
from sqlalchemy import *
from sqlalchemy.ext import declarative
Base = declarative.declarative_base()
"""
class ModelGenerator(object):
"""Various transformations from an A, B diff.
In the implementation, A tends to be called the model and B
the database (although this is not true of all diffs).
The diff is directionless, but transformations apply the diff
in a particular direction, described in the method name.
"""
def __init__(self, diff, engine, declarative=False):
self.diff = diff
self.engine = engine
self.declarative = declarative
def column_repr(self, col):
kwarg = []
if col.key != col.name:
kwarg.append('key')
if col.primary_key:
col.primary_key = True # otherwise it dumps it as 1
kwarg.append('primary_key')
if not col.nullable:
kwarg.append('nullable')
if col.onupdate:
kwarg.append('onupdate')
if col.default:
if col.primary_key:
# I found that PostgreSQL automatically creates a
# default value for the sequence, but let's not show
# that.
pass
else:
kwarg.append('default')
args = ['%s=%r' % (k, getattr(col, k)) for k in kwarg]
# crs: not sure if this is good idea, but it gets rid of extra
# u''
name = col.name.encode('utf8')
type_ = col.type
for cls in col.type.__class__.__mro__:
if cls.__module__ == 'sqlalchemy.types' and \
not cls.__name__.isupper():
if cls is not type_.__class__:
type_ = cls()
break
type_repr = repr(type_)
if type_repr.endswith('()'):
type_repr = type_repr[:-2]
constraints = [repr(cn) for cn in col.constraints]
data = {
'name': name,
'commonStuff': ', '.join([type_repr] + constraints + args),
}
if self.declarative:
return """%(name)s = Column(%(commonStuff)s)""" % data
else:
return """Column(%(name)r, %(commonStuff)s)""" % data
def _getTableDefn(self, table, metaName='meta'):
out = []
tableName = table.name
if self.declarative:
out.append("class %(table)s(Base):" % {'table': tableName})
out.append(" __tablename__ = '%(table)s'\n" %
{'table': tableName})
for col in table.columns:
out.append(" %s" % self.column_repr(col))
out.append('\n')
else:
out.append("%(table)s = Table('%(table)s', %(meta)s," %
{'table': tableName, 'meta': metaName})
for col in table.columns:
out.append(" %s," % self.column_repr(col))
out.append(")\n")
return out
def _get_tables(self,missingA=False,missingB=False,modified=False):
to_process = []
for bool_,names,metadata in (
(missingA,self.diff.tables_missing_from_A,self.diff.metadataB),
(missingB,self.diff.tables_missing_from_B,self.diff.metadataA),
(modified,self.diff.tables_different,self.diff.metadataA),
):
if bool_:
for name in names:
yield metadata.tables.get(name)
def genBDefinition(self):
"""Generates the source code for a definition of B.
Assumes a diff where A is empty.
Was: toPython. Assume database (B) is current and model (A) is empty.
"""
out = []
if self.declarative:
out.append(DECLARATIVE_HEADER)
else:
out.append(HEADER)
out.append("")
for table in self._get_tables(missingA=True):
out.extend(self._getTableDefn(table))
return '\n'.join(out)
def genB2AMigration(self, indent=' '):
'''Generate a migration from B to A.
Was: toUpgradeDowngradePython
Assume model (A) is most current and database (B) is out-of-date.
'''
decls = ['from migrate.changeset import schema',
'pre_meta = MetaData()',
'post_meta = MetaData()',
]
upgradeCommands = ['pre_meta.bind = migrate_engine',
'post_meta.bind = migrate_engine']
downgradeCommands = list(upgradeCommands)
for tn in self.diff.tables_missing_from_A:
pre_table = self.diff.metadataB.tables[tn]
decls.extend(self._getTableDefn(pre_table, metaName='pre_meta'))
upgradeCommands.append(
"pre_meta.tables[%(table)r].drop()" % {'table': tn})
downgradeCommands.append(
"pre_meta.tables[%(table)r].create()" % {'table': tn})
for tn in self.diff.tables_missing_from_B:
post_table = self.diff.metadataA.tables[tn]
decls.extend(self._getTableDefn(post_table, metaName='post_meta'))
upgradeCommands.append(
"post_meta.tables[%(table)r].create()" % {'table': tn})
downgradeCommands.append(
"post_meta.tables[%(table)r].drop()" % {'table': tn})
for (tn, td) in self.diff.tables_different.iteritems():
if td.columns_missing_from_A or td.columns_different:
pre_table = self.diff.metadataB.tables[tn]
decls.extend(self._getTableDefn(
pre_table, metaName='pre_meta'))
if td.columns_missing_from_B or td.columns_different:
post_table = self.diff.metadataA.tables[tn]
decls.extend(self._getTableDefn(
post_table, metaName='post_meta'))
for col in td.columns_missing_from_A:
upgradeCommands.append(
'pre_meta.tables[%r].columns[%r].drop()' % (tn, col))
downgradeCommands.append(
'pre_meta.tables[%r].columns[%r].create()' % (tn, col))
for col in td.columns_missing_from_B:
upgradeCommands.append(
'post_meta.tables[%r].columns[%r].create()' % (tn, col))
downgradeCommands.append(
'post_meta.tables[%r].columns[%r].drop()' % (tn, col))
for modelCol, databaseCol, modelDecl, databaseDecl in td.columns_different:
upgradeCommands.append(
'assert False, "Can\'t alter columns: %s:%s=>%s"' % (
tn, modelCol.name, databaseCol.name))
downgradeCommands.append(
'assert False, "Can\'t alter columns: %s:%s=>%s"' % (
tn, modelCol.name, databaseCol.name))
return (
'\n'.join(decls),
'\n'.join('%s%s' % (indent, line) for line in upgradeCommands),
'\n'.join('%s%s' % (indent, line) for line in downgradeCommands))
def _db_can_handle_this_change(self,td):
"""Check if the database can handle going from B to A."""
if (td.columns_missing_from_B
and not td.columns_missing_from_A
and not td.columns_different):
# Even sqlite can handle column additions.
return True
else:
return not self.engine.url.drivername.startswith('sqlite')
def runB2A(self):
"""Goes from B to A.
Was: applyModel. Apply model (A) to current database (B).
"""
meta = sqlalchemy.MetaData(self.engine)
for table in self._get_tables(missingA=True):
table = table.tometadata(meta)
table.drop()
for table in self._get_tables(missingB=True):
table = table.tometadata(meta)
table.create()
for modelTable in self._get_tables(modified=True):
tableName = modelTable.name
modelTable = modelTable.tometadata(meta)
dbTable = self.diff.metadataB.tables[tableName]
td = self.diff.tables_different[tableName]
if self._db_can_handle_this_change(td):
for col in td.columns_missing_from_B:
modelTable.columns[col].create()
for col in td.columns_missing_from_A:
dbTable.columns[col].drop()
# XXX handle column changes here.
else:
# Sqlite doesn't support drop column, so you have to
# do more: create temp table, copy data to it, drop
# old table, create new table, copy data back.
#
# I wonder if this is guaranteed to be unique?
tempName = '_temp_%s' % modelTable.name
def getCopyStatement():
preparer = self.engine.dialect.preparer
commonCols = []
for modelCol in modelTable.columns:
if modelCol.name in dbTable.columns:
commonCols.append(modelCol.name)
commonColsStr = ', '.join(commonCols)
return 'INSERT INTO %s (%s) SELECT %s FROM %s' % \
(tableName, commonColsStr, commonColsStr, tempName)
# Move the data in one transaction, so that we don't
# leave the database in a nasty state.
connection = self.engine.connect()
trans = connection.begin()
try:
connection.execute(
'CREATE TEMPORARY TABLE %s as SELECT * from %s' % \
(tempName, modelTable.name))
# make sure the drop takes place inside our
# transaction with the bind parameter
modelTable.drop(bind=connection)
modelTable.create(bind=connection)
connection.execute(getCopyStatement())
connection.execute('DROP TABLE %s' % tempName)
trans.commit()
except:
trans.rollback()
raise
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