# Database access

    if hasattr(cur, 'query'): return cur.query

    elif hasattr(cur, '_last_executed'): return cur._last_executed

    else: return None

    def __init__(self, cols, cause=None):

        DbException.__init__(self, 'columns: ' + ', '.join(cols), cause)

        self.cols = cols

class DbWarning(UserWarning): pass

    if re.search(r'\W', name) != None: raise NameException('Name "'+name

        +'" may contain only alphanumeric characters and _')

        # Don't enclose in quotes because this disables case-insensitivity

    'MySQL': ('MySQLdb', {'password': 'passwd', 'database': 'db'}),

    'PostgreSQL': ('psycopg2', {}),

}

DatabaseErrors_set = set([DbException])

DatabaseErrors = tuple(DatabaseErrors_set)

def _add_module(module):

    DatabaseErrors_set.add(module.DatabaseError)

    global DatabaseErrors

    DatabaseErrors = tuple(DatabaseErrors_set)

def db_config_str(db_config):

    return db_config['engine']+' database '+db_config['database']

        self.serializable = serializable

        self.__db = None

    def __getattr__(self, name):

        if name == '__dict__': raise Exception('getting __dict__')

        if name == 'db': return self._db()

        else: raise AttributeError()

    def __getstate__(self):

        state = copy.copy(self.__dict__) # shallow copy

        return state

    def _db(self):

        if self.__db == None:

            # Process db_config

            db_config = self.db_config.copy() # don't modify input!

            module_name, mappings = db_engines[db_config.pop('engine')]

            module = __import__(module_name)

            _add_module(module)

            for orig, new in mappings.iteritems():

                try: util.rename_key(db_config, orig, new)

                except KeyError: pass

            # Connect

            self.__db = module.connect(**db_config)

            # Configure connection

            if self.serializable: run_raw_query(self,

                'SET TRANSACTION ISOLATION LEVEL SERIALIZABLE')

        return self.__db

            else: self.query_results = None

            self.query_lookup = _query_lookup(query, params)

            except Exception, e:

                self.result = e # cache the exception as the result

                self._cache_result()

                raise

            finally: self.query = get_cur_query(self.inner)

            row = self.inner.fetchone()

            # otherwise, fetched all rows

            return row

        def _cache_result(self):

            # For inserts, only cache exceptions since inserts are not

            # idempotent, but an invalid insert will always be invalid

            if self.query_results != None and (not is_insert

                or isinstance(self.result, Exception)):

                    util.dict_subset(dicts.AttrsDictView(self),

                    ['query', 'result', 'rowcount', 'description']))

        def _is_insert(self): return self.query.upper().find('INSERT') >= 0

            def __init__(self, cached_result): self.__dict__ = cached_result

            def execute(self):

                if isinstance(self.result, Exception): raise self.result

                # otherwise, result is a rows list

                self.iter = iter(self.result)

            def fetchone(self):

                try: return self.iter.next()

                except StopIteration: return None

        query_lookup = _query_lookup(query, params)

        try:

            try:

                if not cacheable: raise KeyError

            except KeyError:

                cur = self.DbCursor(self, cacheable)

                try: cur.execute(query, params)

                except Exception, e:

                    _add_cursor_info(e, cur)

                    raise

            if self.log_debug != log_debug_none: # only compute msg if needed

                if used_cache: cache_status = 'Cache hit'

                elif cacheable: cache_status = 'Cache miss'

                else: cache_status = 'Non-cacheable'

                self.log_debug(cache_status+': '+strings.one_line(cur.query))

        return cur

    def is_cached(self, query, params=None):

        return _query_lookup(query, params) in self.query_results

    '''For args, see DbConn.run_query()'''

    return db.run_query(*args, **kw_args)

    except:

    else:

        return with_savepoint(db, run)

    else: return run() # don't need savepoint if cached

def rows(cur): return iter(lambda: cur.fetchone(), None)

    row_iter = rows(cur)

    row_ = row_iter.next()

    iters.consume_iter(row_iter) # fetch all rows so result will be cached

    return row_

def next_value(cur): return next_row(cur)[0]

def value_or_none(cur):

    try: return value(cur)

    except StopIteration: return None

##### Basic queries

    if conds == None: conds = {}

        else: cond_ += '='

        cond_ += ' %s'

        return cond_

    if fields == None: query += '*'

    else: query += ', '.join([esc_name(db, field) for field in fields])

    query += ' FROM '+esc_name(db, table)

    missing = True

        query += ' WHERE '+' AND '.join(map(cond, conds.iteritems()))

    if limit != None: query += ' LIMIT '+str(limit); missing = False

    if start != None:

        if start != 0: query += ' OFFSET '+str(start)

        missing = False

    if missing: warnings.warn(DbWarning(

        'SELECT statement missing a WHERE, LIMIT, or OFFSET clause: '+query))

        +', '.join(['%s']*len(cols))+')'

    else: query += ' DEFAULT VALUES'

    if returning != None:

        check_name(returning)

        query += ' RETURNING '+returning

    elif module == 'MySQLdb': return db.insert_id()

    else: return None

    check_name(table)

##### Database structure queries

    check_name(table)

        'SELECT * FROM '+table+' LIMIT 0', recover=recover)).next()

    '''Can also use this for UNIQUE constraints, because a UNIQUE index is

    automatically created. When you don't know whether something is a UNIQUE

    constraint or a UNIQUE index, use this function.'''

    check_name(table)

    check_name(index)

    if module == 'psycopg2':

        return list(values(run_query(db, '''\

(

        SELECT attnum, attname

        FROM pg_index

        JOIN pg_class index ON index.oid = indexrelid

        JOIN pg_class table_ ON table_.oid = indrelid

        JOIN pg_attribute ON attrelid = indrelid AND attnum = ANY (indkey)

        WHERE

            table_.relname = %(table)s

            AND index.relname = %(index)s

    UNION

        SELECT attnum, attname

        FROM

        (

            SELECT

                indrelid

                , (regexp_matches(indexprs, E':varattno (\\\\d+)', 'g'))[1]::int

                    AS indkey

            FROM pg_index

            JOIN pg_class index ON index.oid = indexrelid

            JOIN pg_class table_ ON table_.oid = indrelid

            WHERE

                table_.relname = %(table)s

                AND index.relname = %(index)s

        ) s

        JOIN pg_attribute ON attrelid = indrelid AND attnum = indkey

) s

''',

    else: raise NotImplementedError("Can't list index columns for "+module+

        ' database')

    check_name(table)

    check_name(constraint)

        return list(values(run_query(db, '''\

SELECT attname

FROM pg_constraint

JOIN pg_class ON pg_class.oid = conrelid

JOIN pg_attribute ON attrelid = conrelid AND attnum = ANY (conkey)

WHERE

    relname = %(table)s

    AND conname = %(constraint)s

ORDER BY attnum

''',

            {'table': table, 'constraint': constraint})))

    else: raise NotImplementedError("Can't list constraint columns for "+module+

        ' database')

        return values(run_query(db, "SELECT tablename from pg_tables "

            "WHERE schemaname = 'public' ORDER BY tablename"))

    elif module == 'MySQLdb': return values(run_query(db, 'SHOW TABLES'))

    else: raise NotImplementedError("Can't list tables for "+module+' database')

def empty_db(db):

    for table in tables(db): truncate(db, table)

        msg = str(e)

            r'"(([^\W_]+)_[^"]+)"', msg)

        if match:

            constraint, table = match.groups()

            'constraint', msg)

    Only works under PostgreSQL (uses `INSERT ... RETURNING`)'''

        if row_ct_ref != None and cur.rowcount >= 0:

            row_ct_ref[0] += cur.rowcount

        return value(cur)

            util.dict_subset_right_join(row, e.cols), recover=True))

    try: return value(select(db, table, [pkey], row, 1, recover=True))