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dbapi.py
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dbapi.py
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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
This module implements the Python DBAPI 2.0 as described in
https://www.python.org/dev/peps/pep-0249/ .
Fetch methods returns rows as a list of lists on purpose to let the caller
decide to convert then to a list of tuples.
"""
from __future__ import absolute_import, division, print_function
import binascii
import datetime
import logging
import uuid
from typing import Any, List, Optional # NOQA for mypy types
import prestodb.client
import prestodb.exceptions
import prestodb.redirect
from prestodb import constants
from prestodb.transaction import IsolationLevel, NO_TRANSACTION, Transaction
from prestodb.transaction import NO_TRANSACTION
__all__ = ["connect", "Connection", "Cursor"]
apilevel = "2.0"
threadsafety = 2
logger = logging.getLogger(__name__)
def connect(*args, **kwargs):
"""Constructor for creating a connection to the database.
See class :py:class:`Connection` for arguments.
:returns: a :py:class:`Connection` object.
"""
return Connection(*args, **kwargs)
class Connection(object):
"""Presto supports transactions and the ability to either commit or rollback
a sequence of SQL statements. A single query i.e. the execution of a SQL
statement, can also be cancelled. Transactions are not supported by this
client implementation yet.
"""
def __init__(
self,
host,
port=constants.DEFAULT_PORT,
user=None,
source=constants.DEFAULT_SOURCE,
catalog=constants.DEFAULT_CATALOG,
schema=constants.DEFAULT_SCHEMA,
session_properties=None,
http_headers=None,
http_scheme=constants.HTTP,
auth=constants.DEFAULT_AUTH,
redirect_handler=prestodb.redirect.GatewayRedirectHandler(),
max_attempts=constants.DEFAULT_MAX_ATTEMPTS,
request_timeout=constants.DEFAULT_REQUEST_TIMEOUT,
isolation_level=IsolationLevel.AUTOCOMMIT,
**kwargs,
):
self.host = host
self.port = port
self.user = user
self.source = source
self.catalog = catalog
self.schema = schema
self.session_properties = session_properties
self._client_session = prestodb.client.ClientSession(
user,
catalog,
schema,
source,
session_properties,
http_headers,
NO_TRANSACTION,
)
# mypy cannot follow module import
self._http_session = prestodb.client.PrestoRequest.http.Session()
self.http_headers = http_headers
self.http_scheme = http_scheme
self.auth = auth
self.redirect_handler = redirect_handler
self.max_attempts = max_attempts
self.request_timeout = request_timeout
self._isolation_level = isolation_level
self._request = None
self._transaction = None
@property
def isolation_level(self):
return self._isolation_level
@property
def transaction(self):
return self._transaction
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
try:
self.commit()
except Exception:
self.rollback()
else:
self.close()
def close(self):
"""Presto does not have anything to close"""
# TODO cancel outstanding queries?
pass
def start_transaction(self):
self._transaction = Transaction(self._create_request())
self._transaction.begin()
return self._transaction
def commit(self):
if self.transaction is None:
return
self._transaction.commit()
self._transaction = None
def rollback(self):
if self.transaction is None:
raise RuntimeError("no transaction was started")
self._transaction.rollback()
self._transaction = None
def _create_request(self):
return prestodb.client.PrestoRequest(
self.host,
self.port,
self._client_session,
self._http_session,
self.http_headers,
NO_TRANSACTION,
self.http_scheme,
self.auth,
self.redirect_handler,
self.max_attempts,
self.request_timeout,
)
def cursor(self):
"""Return a new :py:class:`Cursor` object using the connection."""
if self.isolation_level != IsolationLevel.AUTOCOMMIT:
if self.transaction is None:
self.start_transaction()
request = self.transaction._request
else:
request = self._create_request()
return Cursor(self, request)
class Cursor(object):
"""Database cursor.
Cursors are not isolated, i.e., any changes done to the database by a
cursor are immediately visible by other cursors or connections.
"""
def __init__(self, connection, request):
if not isinstance(connection, Connection):
raise ValueError(
"connection must be a Connection object: {}".format(type(connection))
)
self._connection = connection
self._request = request
self.arraysize = 1
self._iterator = None
self._query = None
def __iter__(self):
return self._iterator
@property
def connection(self):
return self._connection
@property
def description(self):
if self._query.columns is None:
return None
# [ (name, type_code, display_size, internal_size, precision, scale, null_ok) ]
return [
(col["name"], col["type"], None, None, None, None, None)
for col in self._query.columns
]
@property
def rowcount(self):
"""Not supported.
Presto cannot reliablity determine the number of rows returned by an
operation. For example, the result of a SELECT query is streamed and
the number of rows is only knowns when all rows have been retrieved.
"""
return -1
@property
def stats(self):
if self._query is not None:
return self._query.stats
return None
@property
def warnings(self):
if self._query is not None:
return self._query.warnings
return None
def setinputsizes(self, sizes):
raise prestodb.exceptions.NotSupportedError
def setoutputsize(self, size, column):
raise prestodb.exceptions.NotSupportedError
def execute(self, operation, params=None):
if params:
assert isinstance(params, (list, tuple)), (
"params must be a list or tuple containing the query "
"parameter values"
)
statement_name = self._generate_unique_statement_name()
self._prepare_statement(operation, statement_name)
try:
# Send execute statement and assign the return value to `results`
# as it will be returned by the function
self._query = self._execute_prepared_statement(statement_name, params)
self._iterator = iter(self._query.execute())
finally:
# Send deallocate statement
# At this point the query can be deallocated since it has already
# been executed
# TODO: Consider caching prepared statements if requested by caller
self._deallocate_prepared_statement(statement_name)
else:
self._query = prestodb.client.PrestoQuery(self._request, sql=operation)
self._iterator = iter(self._query.execute())
return self
def _generate_unique_statement_name(self):
return "st_" + uuid.uuid4().hex.replace("-", "")
def _prepare_statement(self, statement: str, name: str) -> None:
sql = f"PREPARE {name} FROM {statement}"
query = prestodb.client.PrestoQuery(self._request, sql=sql)
query.execute()
def _execute_prepared_statement(self, statement_name, params):
sql = (
"EXECUTE "
+ statement_name
+ " USING "
+ ",".join(map(self._format_prepared_param, params))
)
return prestodb.client.PrestoQuery(self._request, sql=sql)
def _deallocate_prepared_statement(self, statement_name: str) -> None:
sql = "DEALLOCATE PREPARE " + statement_name
query = prestodb.client.PrestoQuery(self._request, sql=sql)
query.execute()
def _format_prepared_param(self, param):
"""
Formats parameters to be passed in an
EXECUTE statement.
"""
if param is None:
return "NULL"
if isinstance(param, bool):
return "true" if param else "false"
if isinstance(param, int):
# TODO represent numbers exceeding 64-bit (BIGINT) as DECIMAL
return "%d" % param
if isinstance(param, float):
if param == float("+inf"):
return "infinity()"
if param == float("-inf"):
return "-infinity()"
return "DOUBLE '%s'" % param
if isinstance(param, str):
return "'%s'" % param.replace("'", "''")
if isinstance(param, bytes):
return "X'%s'" % param.hex()
if isinstance(param, datetime.datetime) and param.tzinfo is None:
datetime_str = param.strftime("%Y-%m-%d %H:%M:%S.%f")
return "TIMESTAMP '%s'" % datetime_str
if isinstance(param, datetime.datetime) and param.tzinfo is not None:
datetime_str = param.strftime("%Y-%m-%d %H:%M:%S.%f")
# offset-based timezones
return "TIMESTAMP '%s %s'" % (datetime_str, param.tzinfo.tzname(param))
# We can't calculate the offset for a time without a point in time
if isinstance(param, datetime.time) and param.tzinfo is None:
time_str = param.strftime("%H:%M:%S.%f")
return "TIME '%s'" % time_str
if isinstance(param, datetime.time) and param.tzinfo is not None:
time_str = param.strftime("%H:%M:%S.%f")
# offset-based timezones
return "TIME '%s %s'" % (time_str, param.strftime("%Z")[3:])
if isinstance(param, datetime.date):
date_str = param.strftime("%Y-%m-%d")
return "DATE '%s'" % date_str
if isinstance(param, list):
return "ARRAY[%s]" % ",".join(map(self._format_prepared_param, param))
if isinstance(param, tuple):
return "ROW(%s)" % ",".join(map(self._format_prepared_param, param))
if isinstance(param, dict):
keys = list(param.keys())
values = [param[key] for key in keys]
return "MAP({}, {})".format(
self._format_prepared_param(keys), self._format_prepared_param(values)
)
if isinstance(param, uuid.UUID):
return "UUID '%s'" % param
if isinstance(param, (bytes, bytearray)):
return "X'%s'" % binascii.hexlify(param).decode("utf-8")
raise prestodb.exceptions.NotSupportedError(
"Query parameter of type '%s' is not supported." % type(param)
)
def executemany(self, operation, seq_of_params):
raise prestodb.exceptions.NotSupportedError
def fetchone(self):
# type: () -> Optional[List[Any]]
"""
PEP-0249: Fetch the next row of a query result set, returning a single
sequence, or None when no more data is available.
An Error (or subclass) exception is raised if the previous call to
.execute*() did not produce any result set or no call was issued yet.
"""
try:
return next(self._iterator)
except StopIteration:
return None
except prestodb.exceptions.HttpError as err:
raise prestodb.exceptions.OperationalError(str(err))
def fetchmany(self, size=None):
# type: (Optional[int]) -> List[List[Any]]
"""
PEP-0249: Fetch the next set of rows of a query result, returning a
sequence of sequences (e.g. a list of tuples). An empty sequence is
returned when no more rows are available.
The number of rows to fetch per call is specified by the parameter. If
it is not given, the cursor's arraysize determines the number of rows
to be fetched. The method should try to fetch as many rows as indicated
by the size parameter. If this is not possible due to the specified
number of rows not being available, fewer rows may be returned.
An Error (or subclass) exception is raised if the previous call to
.execute*() did not produce any result set or no call was issued yet.
Note there are performance considerations involved with the size
parameter. For optimal performance, it is usually best to use the
.arraysize attribute. If the size parameter is used, then it is best
for it to retain the same value from one .fetchmany() call to the next.
"""
if size is None:
size = self.arraysize
result = []
for _ in range(size):
row = self.fetchone()
if row is None:
break
result.append(row)
return result
def genall(self):
return self._query.result
def fetchall(self):
# type: () -> List[List[Any]]
return list(self.genall())
def cancel(self):
if self._query is None:
raise prestodb.exceptions.OperationalError(
"Cancel query failed; no running query"
)
self._query.cancel()
def close(self):
self._connection.close()
Date = datetime.date
Time = datetime.time
Timestamp = datetime.datetime
DateFromTicks = datetime.date.fromtimestamp
TimestampFromTicks = datetime.datetime.fromtimestamp
def TimeFromTicks(ticks):
return datetime.time(*datetime.localtime(ticks)[3:6])
def Binary(string):
return string.encode("utf-8")
class DBAPITypeObject:
def __init__(self, *values):
self.values = [v.lower() for v in values]
def __eq__(self, other):
return other.lower() in self.values
STRING = DBAPITypeObject("VARCHAR", "CHAR", "VARBINARY", "JSON", "IPADDRESS")
BINARY = DBAPITypeObject(
"ARRAY", "MAP", "ROW", "HyperLogLog", "P4HyperLogLog", "QDigest"
)
NUMBER = DBAPITypeObject(
"BOOLEAN", "TINYINT", "SMALLINT", "INTEGER", "BIGINT", "REAL", "DOUBLE", "DECIMAL"
)
DATETIME = DBAPITypeObject(
"DATE",
"TIME",
"TIME WITH TIME ZONE",
"TIMESTAMP",
"TIMESTAMP WITH TIME ZONE",
"INTERVAL YEAR TO MONTH",
"INTERVAL DAY TO SECOND",
)
ROWID = DBAPITypeObject() # nothing indicates row id in Presto