root/django/trunk/contrib/evolve.py

import os, re, sys
sys.path.append('contrib')
sys.path.append(os.getcwd())
from django.core.management import setup_environ
import settings
setup_environ(settings)

try:
    app = sys.argv[1]
except IndexError:
    sys.stderr.write("Usage: evolve.py <appname>")
    sys.exit(1)

assert settings.DATABASE_ENGINE == 'sqlite3'
database = settings.DATABASE_NAME

class Table(object):
    name_line = re.compile(r'CREATE TABLE "(.+)" \(')
    field_line = re.compile(r'^"([^"]+)".*')

    def __init__(self, sql):
        lines = sql.splitlines()
        self.name = self.getTableName(lines[0])
        self.old_fields = {}
        for line in lines[1:-1]: # remove create table and closing bracket
            line = line.strip().strip(',')
            self.old_fields[self.getFieldName(line)] = line
        self.new_fields = []

    def new(self, sql):
        self.new_fields = [line.strip().strip(',') for line in sql.splitlines()[1:-1]] # remove create table and closing bracket


    def getTableName(self, sql):
        return self.name_line.search(sql).groups()[0]
    def getFieldName(self, sql):
        s = self.field_line.search(sql)
        if not s:
            return None
        else:
            return s.groups()[0]
    def getFieldOption(self, field, option):
        a, m = self.name.split('_', 1)
        module = __import__('%s.models' % app, {}, {}, [m.capitalize()])
        model = getattr(module, m.capitalize())
        f = model._meta.get_field(field)
        return getattr(f, option, None)
    def getFieldAka(self, field):
        return self.getFieldOption(field, 'aka')
    def getFieldDefault(self, field):
        return self.getFieldOption(field, 'default')

    def getSql(self):
        name = self.name

        new_fields = []
        old_fields = []
        new_columns = []

        for field_sql in self.new_fields:
            field_name = self.getFieldName(field_sql)
            if not field_name: continue
            new_fields.append(field_sql)
            if field_name not in self.old_fields:
                aka = self.getFieldAka(field_name)
                if aka:
                    # field renamed
                    old_fields.append('"%s"' % aka)
                else:
                    # field added
                    old_fields.append('"%s"' % field_name)
                    default = self.getFieldDefault(field_name)
                    if default is not None:
                        new_columns.append('ALTER TABLE "%s__temp__" ADD COLUMN %s DEFAULT "%s";' % (self.name, field_sql, default))

                    else:
                        new_columns.append('ALTER TABLE "%s__temp__" ADD COLUMN %s;' % (self.name, field_sql))
            else:
                # field not changed (or slightly tweaked)
                old_fields.append('"%s"' % field_name)

        return """
        ALTER TABLE "%(name)s" RENAME TO "%(name)s__temp__";

        %(new_columns)s

        CREATE TABLE "%(name)s" (
           %(new_fields)s
        );

        INSERT INTO "%(name)s" SELECT %(old_fields)s FROM "%(name)s__temp__";
        DROP TABLE "%(name)s__temp__";
        """ % dict(name=name, new_columns='\n'.join(new_columns), new_fields=',\n'.join(new_fields), old_fields=', '.join(old_fields))

if __name__=='__main__':
    new_tables_sql = os.popen('manage.py sql %s' % app).read()
    old_tables_sql = os.popen('sqlite3 %s ".schema %s_%%"' % (database, app)).read()

    # remove control characters
    ctrl = re.compile(r'[\000-\011\013-\037]')
    new_tables_sql = ctrl.sub('', new_tables_sql)
    old_tables_sql = ctrl.sub('', old_tables_sql)

    new_tables_sql = new_tables_sql.split(';')[1:-2] # remove begin, commit and empty ; at the end
    old_tables_sql = old_tables_sql.split(';')[:-1] # remove empty ; at the end

    tables = {}

    for sql in old_tables_sql:
        if 'CREATE INDEX' in sql: continue
        t = Table(sql.strip())
        tables[t.name] = t

    for sql in new_tables_sql:
        if 'CREATE INDEX' in sql: continue
        t = Table(sql.strip())
        tables[t.name].new(sql.strip())

    for table in tables.values():
        print table.getSql()