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##
# .api - ABCs for database interface elements
##
"""
Application Programmer Interfaces for PostgreSQL.
``postgresql.api`` is a collection of Python APIs for the PostgreSQL DBMS. It
is designed to take full advantage of PostgreSQL's features to provide the
Python programmer with substantial convenience.
This module is used to define "PG-API". It creates a set of ABCs
that makes up the basic interfaces used to work with a PostgreSQL server.
"""
import collections.abc
import abc
from .python.element import Element
__all__ = [
'Message',
'Statement',
'Chunks',
'Cursor',
'Connector',
'Category',
'Database',
'TypeIO',
'Connection',
'Transaction',
'Settings',
'StoredProcedure',
'Driver',
'Installation',
'Cluster',
]
class Message(Element):
"""
A message emitted by PostgreSQL.
A message being a NOTICE, WARNING, INFO, etc.
"""
_e_label = 'MESSAGE'
severities = (
'DEBUG',
'INFO',
'NOTICE',
'WARNING',
'ERROR',
'FATAL',
'PANIC',
)
sources = (
'SERVER',
'CLIENT',
)
@property
@abc.abstractmethod
def source(self) -> str:
"""
Where the message originated from. Normally, 'SERVER', but sometimes
'CLIENT'.
"""
@property
@abc.abstractmethod
def code(self) -> str:
"""
The SQL state code of the message.
"""
@property
@abc.abstractmethod
def message(self) -> str:
"""
The primary message string.
"""
@property
@abc.abstractmethod
def details(self) -> dict:
"""
The additional details given with the message. Common keys *should* be the
following:
* 'severity'
* 'context'
* 'detail'
* 'hint'
* 'file'
* 'line'
* 'function'
* 'position'
* 'internal_position'
* 'internal_query'
"""
@abc.abstractmethod
def isconsistent(self, other) -> bool:
"""
Whether the fields of the `other` Message object is consistent with the
fields of `self`.
This *must* return the result of the comparison of code, source, message,
and details.
This method is provided as the alternative to overriding equality;
often, pointer equality is the desirable means for comparison, but
equality of the fields is also necessary.
"""
class Result(Element):
"""
A result is an object managing the results of a prepared statement.
These objects represent a binding of parameters to a given statement object.
For results that were constructed on the server and a reference passed back
to the client, statement and parameters may be None.
"""
_e_label = 'RESULT'
_e_factors = ('statement', 'parameters', 'cursor_id')
@abc.abstractmethod
def close(self) -> None:
"""
Close the Result discarding any supporting resources and causing
future read operations to emit empty record sets.
"""
@property
@abc.abstractmethod
def cursor_id(self) -> str:
"""
The cursor's identifier.
"""
@property
@abc.abstractmethod
def sql_column_types(self) -> [str]:
"""
The type of the columns produced by the cursor.
A sequence of `str` objects stating the SQL type name::
['INTEGER', 'CHARACTER VARYING', 'INTERVAL']
"""
@property
@abc.abstractmethod
def pg_column_types(self) -> [int]:
"""
The type Oids of the columns produced by the cursor.
A sequence of `int` objects stating the SQL type name::
[27, 28]
"""
@property
@abc.abstractmethod
def column_names(self) -> [str]:
"""
The attribute names of the columns produced by the cursor.
A sequence of `str` objects stating the column name::
['column1', 'column2', 'emp_name']
"""
@property
@abc.abstractmethod
def column_types(self) -> [str]:
"""
The Python types of the columns produced by the cursor.
A sequence of type objects::
[<class 'int'>, <class 'str'>]
"""
@property
@abc.abstractmethod
def parameters(self) -> (tuple, None):
"""
The parameters bound to the cursor. `None`, if unknown and an empty tuple
`()`, if no parameters were given.
These should be the *original* parameters given to the invoked statement.
This should only be `None` when the cursor is created from an identifier,
`postgresql.api.Database.cursor_from_id`.
"""
@property
@abc.abstractmethod
def statement(self) -> ("Statement", None):
"""
The query object used to create the cursor. `None`, if unknown.
This should only be `None` when the cursor is created from an identifier,
`postgresql.api.Database.cursor_from_id`.
"""
@collections.abc.Iterator.register
class Chunks(Result):
pass
@collections.abc.Iterator.register
class Cursor(Result):
"""
A `Cursor` object is an interface to a sequence of tuples(rows). A result
set. Cursors publish a file-like interface for reading tuples from a cursor
declared on the database.
`Cursor` objects are created by invoking the `Statement.declare`
method or by opening a cursor using an identifier via the
`Database.cursor_from_id` method.
"""
_e_label = 'CURSOR'
_seek_whence_map = {
0 : 'ABSOLUTE',
1 : 'RELATIVE',
2 : 'FROM_END',
3 : 'FORWARD',
4 : 'BACKWARD'
}
_direction_map = {
True : 'FORWARD',
False : 'BACKWARD',
}
@abc.abstractmethod
def clone(self) -> "Cursor":
"""
Create a new cursor using the same factors as `self`.
"""
def __iter__(self):
return self
@property
@abc.abstractmethod
def direction(self) -> bool:
"""
The default `direction` argument for read().
When `True` reads are FORWARD.
When `False` reads are BACKWARD.
Cursor operation option.
"""
@abc.abstractmethod
def read(self, quantity = None, direction = None) -> ["Row"]:
"""
Read, fetch, the specified number of rows and return them in a list.
If quantity is `None`, all records will be fetched.
`direction` can be used to override the default configured direction.
This alters the cursor's position.
Read does not directly correlate to FETCH. If zero is given as the
quantity, an empty sequence *must* be returned.
"""
@abc.abstractmethod
def __next__(self) -> "Row":
"""
Get the next tuple in the cursor.
Advances the cursor position by one.
"""
@abc.abstractmethod
def seek(self, offset, whence = 'ABSOLUTE'):
"""
Set the cursor's position to the given offset with respect to the
whence parameter and the configured direction.
Whence values:
``0`` or ``"ABSOLUTE"``
Absolute.
``1`` or ``"RELATIVE"``
Relative.
``2`` or ``"FROM_END"``
Absolute from end.
``3`` or ``"FORWARD"``
Relative forward.
``4`` or ``"BACKWARD"``
Relative backward.
Direction effects whence. If direction is BACKWARD, ABSOLUTE positioning
will effectively be FROM_END, RELATIVE's position will be negated, and
FROM_END will effectively be ABSOLUTE.
"""
class Execution(metaclass = abc.ABCMeta):
"""
The abstract class of execution methods.
"""
@abc.abstractmethod
def __call__(self, *parameters) -> ["Row"]:
"""
Execute the prepared statement with the given arguments as parameters.
Usage:
>>> p=db.prepare("SELECT column FROM ttable WHERE key = $1")
>>> p('identifier')
[...]
"""
@abc.abstractmethod
def column(self, *parameters) -> collections.abc.Iterable:
"""
Return an iterator producing the values of first column of the
rows produced by the cursor created from the statement bound with the
given parameters.
Column iterators are never scrollable.
Supporting cursors will be WITH HOLD when outside of a transaction to
allow cross-transaction access.
`column` is designed for the situations involving large data sets.
Each iteration returns a single value.
column expressed in sibling terms::
return map(operator.itemgetter(0), self.rows(*parameters))
"""
@abc.abstractmethod
def chunks(self, *parameters) -> collections.abc.Iterable:
"""
Return an iterator producing sequences of rows produced by the cursor
created from the statement bound with the given parameters.
Chunking iterators are *never* scrollable.
Supporting cursors will be WITH HOLD when outside of a transaction.
`chunks` is designed for moving large data sets efficiently.
Each iteration returns sequences of rows *normally* of length(seq) ==
chunksize. If chunksize is unspecified, a default, positive integer will
be filled in. The rows contained in the sequences are only required to
support the basic `collections.abc.Sequence` interfaces; simple and quick
sequence types should be used.
"""
@abc.abstractmethod
def rows(self, *parameters) -> collections.abc.Iterable:
"""
Return an iterator producing rows produced by the cursor
created from the statement bound with the given parameters.
Row iterators are never scrollable.
Supporting cursors will be WITH HOLD when outside of a transaction to
allow cross-transaction access.
`rows` is designed for the situations involving large data sets.
Each iteration returns a single row. Arguably, best implemented::
return itertools.chain.from_iterable(self.chunks(*parameters))
"""
@abc.abstractmethod
def column(self, *parameters) -> collections.abc.Iterable:
"""
Return an iterator producing the values of the first column in
the cursor created from the statement bound with the given parameters.
Column iterators are never scrollable.
Supporting cursors will be WITH HOLD when outside of a transaction to
allow cross-transaction access.
`column` is designed for the situations involving large data sets.
Each iteration returns a single value. `column` is equivalent to::
return map(operator.itemgetter(0), self.rows(*parameters))
"""
@abc.abstractmethod
def declare(self, *parameters) -> Cursor:
"""
Return a scrollable cursor with hold using the statement bound with the
given parameters.
"""
@abc.abstractmethod
def first(self, *parameters):
"""
Execute the prepared statement with the given arguments as parameters.
If the statement returns rows with multiple columns, return the first
row. If the statement returns rows with a single column, return the
first column in the first row. If the query does not return rows at all,
return the count or `None` if no count exists in the completion message.
Usage:
>>> db.prepare("SELECT * FROM ttable WHERE key = $1").first("somekey")
('somekey', 'somevalue')
>>> db.prepare("SELECT 'foo'").first()
'foo'
>>> db.prepare("INSERT INTO atable (col) VALUES (1)").first()
1
"""
@abc.abstractmethod
def load_rows(self, iterable):
"""
Given an iterable, `iterable`, feed the produced parameters to the
query. This is a bulk-loading interface for parameterized queries.
Effectively, it is equivalent to:
>>> q = db.prepare(sql)
>>> for i in iterable:
... q(*i)
Its purpose is to allow the implementation to take advantage of the
knowledge that a series of parameters are to be loaded so that the
operation can be optimized.
"""
@abc.abstractmethod
def load_chunks(self, iterable):
"""
Given an iterable, `iterable`, feed the produced parameters of the chunks
produced by the iterable to the query. This is a bulk-loading interface
for parameterized queries.
Effectively, it is equivalent to:
>>> ps = db.prepare(...)
>>> for c in iterable:
... for i in c:
... q(*i)
Its purpose is to allow the implementation to take advantage of the
knowledge that a series of chunks of parameters are to be loaded so
that the operation can be optimized.
"""
@collections.abc.Iterator.register
@collections.abc.Callable.register
@Execution.register
class Statement(Element):
"""
Instances of `Statement` are returned by the `prepare` method of
`Database` instances.
A Statement is an Iterable as well as Callable.
The Iterable interface is supported for queries that take no arguments at
all. It allows the syntax::
>>> for x in db.prepare('select * FROM table'):
... pass
"""
_e_label = 'STATEMENT'
_e_factors = ('database', 'statement_id', 'string',)
@property
@abc.abstractmethod
def statement_id(self) -> str:
"""
The statment's identifier.
"""
@property
@abc.abstractmethod
def string(self) -> object:
"""
The SQL string of the prepared statement.
`None` if not available. This can happen in cases where a statement is
prepared on the server and a reference to the statement is sent to the
client which subsequently uses the statement via the `Database`'s
`statement` constructor.
"""
@property
@abc.abstractmethod
def sql_parameter_types(self) -> [str]:
"""
The type of the parameters required by the statement.
A sequence of `str` objects stating the SQL type name::
['INTEGER', 'VARCHAR', 'INTERVAL']
"""
@property
@abc.abstractmethod
def sql_column_types(self) -> [str]:
"""
The type of the columns produced by the statement.
A sequence of `str` objects stating the SQL type name::
['INTEGER', 'VARCHAR', 'INTERVAL']
"""
@property
@abc.abstractmethod
def pg_parameter_types(self) -> [int]:
"""
The type Oids of the parameters required by the statement.
A sequence of `int` objects stating the PostgreSQL type Oid::
[27, 28]
"""
@property
@abc.abstractmethod
def pg_column_types(self) -> [int]:
"""
The type Oids of the columns produced by the statement.
A sequence of `int` objects stating the SQL type name::
[27, 28]
"""
@property
@abc.abstractmethod
def column_names(self) -> [str]:
"""
The attribute names of the columns produced by the statement.
A sequence of `str` objects stating the column name::
['column1', 'column2', 'emp_name']
"""
@property
@abc.abstractmethod
def column_types(self) -> [type]:
"""
The Python types of the columns produced by the statement.
A sequence of type objects::
[<class 'int'>, <class 'str'>]
"""
@property
@abc.abstractmethod
def parameter_types(self) -> [type]:
"""
The Python types expected of parameters given to the statement.
A sequence of type objects::
[<class 'int'>, <class 'str'>]
"""
@abc.abstractmethod
def clone(self) -> "Statement":
"""
Create a new statement object using the same factors as `self`.
When used for refreshing plans, the new clone should replace references to
the original.
"""
@abc.abstractmethod
def close(self) -> None:
"""
Close the prepared statement releasing resources associated with it.
"""
PreparedStatement = Statement
@collections.abc.Callable.register
class StoredProcedure(Element):
"""
A function stored on the database.
"""
_e_label = 'FUNCTION'
_e_factors = ('database',)
@abc.abstractmethod
def __call__(self, *args, **kw) -> (object, Cursor, collections.abc.Iterable):
"""
Execute the procedure with the given arguments. If keyword arguments are
passed they must be mapped to the argument whose name matches the key.
If any positional arguments are given, they must fill in gaps created by
the stated keyword arguments. If too few or too many arguments are
given, a TypeError must be raised. If a keyword argument is passed where
the procedure does not have a corresponding argument name, then,
likewise, a TypeError must be raised.
In the case where the `StoredProcedure` references a set returning
function(SRF), the result *must* be an iterable. SRFs that return single
columns *must* return an iterable of that column; not row data. If the
SRF returns a composite(OUT parameters), it *should* return a `Cursor`.
"""
##
# Arguably, it would be wiser to isolate blocks, and savepoints, but the utility
# of the separation is not significant. It's really
# more interesting as a formality that the user may explicitly state the
# type of the transaction. However, this capability is not completely absent
# from the current interface as the configuration parameters, or lack thereof,
# help imply the expectations.
class Transaction(Element):
"""
A `Tranaction` is an element that represents a transaction in the session.
Once created, it's ready to be started, and subsequently committed or
rolled back.
Read-only transaction:
>>> with db.xact(mode = 'read only'):
... ...
Read committed isolation:
>>> with db.xact(isolation = 'READ COMMITTED'):
... ...
Savepoints are created if inside a transaction block:
>>> with db.xact():
... with db.xact():
... ...
"""
_e_label = 'XACT'
_e_factors = ('database',)
@property
@abc.abstractmethod
def mode(self) -> (None, str):
"""
The mode of the transaction block:
START TRANSACTION [ISOLATION] <mode>;
The `mode` property is a string and will be directly interpolated into the
START TRANSACTION statement.
"""
@property
@abc.abstractmethod
def isolation(self) -> (None, str):
"""
The isolation level of the transaction block:
START TRANSACTION <isolation> [MODE];
The `isolation` property is a string and will be directly interpolated into
the START TRANSACTION statement.
"""
@abc.abstractmethod
def start(self) -> None:
"""
Start the transaction.
If the database is in a transaction block, the transaction should be
configured as a savepoint. If any transaction block configuration was
applied to the transaction, raise a `postgresql.exceptions.OperationError`.
If the database is not in a transaction block, start one using the
configuration where:
`self.isolation` specifies the ``ISOLATION LEVEL``. Normally, ``READ
COMMITTED``, ``SERIALIZABLE``, or ``READ UNCOMMITTED``.
`self.mode` specifies the mode of the transaction. Normally, ``READ
ONLY`` or ``READ WRITE``.
If the transaction is already open, do nothing.
If the transaction has been committed or aborted, raise an
`postgresql.exceptions.OperationError`.
"""
begin = start
@abc.abstractmethod
def commit(self) -> None:
"""
Commit the transaction.
If the transaction is a block, issue a COMMIT statement.
If the transaction was started inside a transaction block, it should be
identified as a savepoint, and the savepoint should be released.
If the transaction has already been committed, do nothing.
"""
@abc.abstractmethod
def rollback(self) -> None:
"""
Abort the transaction.
If the transaction is a savepoint, ROLLBACK TO the savepoint identifier.
If the transaction is a transaction block, issue an ABORT.
If the transaction has already been aborted, do nothing.
"""
abort = rollback
@abc.abstractmethod
def __enter__(self):
"""
Run the `start` method and return self.
"""
@abc.abstractmethod
def __exit__(self, typ, obj, tb):
"""
If an exception is indicated by the parameters, run the transaction's
`rollback` method iff the database is still available(not closed), and
return a `False` value.
If an exception is not indicated, but the database's transaction state is
in error, run the transaction's `rollback` method and raise a
`postgresql.exceptions.InFailedTransactionError`. If the database is
unavailable, the `rollback` method should cause a
`postgresql.exceptions.ConnectionDoesNotExistError` exception to occur.
Otherwise, run the transaction's `commit` method.
When the `commit` is ultimately unsuccessful or not ran at all, the purpose
of __exit__ is to resolve the error state of the database iff the
database is available(not closed) so that more commands can be after the
block's exit.
"""
@collections.abc.MutableMapping.register
class Settings(Element):
"""
A mapping interface to the session's settings. This provides a direct
interface to ``SHOW`` or ``SET`` commands. Identifiers and values need
not be quoted specially as the implementation must do that work for the
user.
"""
_e_label = 'SETTINGS'
@abc.abstractmethod
def __getitem__(self, key):
"""
Return the setting corresponding to the given key. The result should be
consistent with what the ``SHOW`` command returns. If the key does not
exist, raise a KeyError.
"""
@abc.abstractmethod
def __setitem__(self, key, value):
"""
Set the setting with the given key to the given value. The action should
be consistent with the effect of the ``SET`` command.
"""
@abc.abstractmethod
def __call__(self, **kw):
"""
Create a context manager applying the given settings on __enter__ and
restoring the old values on __exit__.
>>> with db.settings(search_path = 'local,public'):
... ...
"""
@abc.abstractmethod
def get(self, key, default = None):
"""
Get the setting with the corresponding key. If the setting does not
exist, return the `default`.
"""
@abc.abstractmethod
def getset(self, keys):
"""
Return a dictionary containing the key-value pairs of the requested
settings. If *any* of the keys do not exist, a `KeyError` must be raised
with the set of keys that did not exist.
"""
@abc.abstractmethod
def update(self, mapping):
"""
For each key-value pair, incur the effect of the `__setitem__` method.
"""
@abc.abstractmethod
def keys(self):
"""
Return an iterator to all of the settings' keys.
"""
@abc.abstractmethod
def values(self):
"""
Return an iterator to all of the settings' values.
"""
@abc.abstractmethod
def items(self):
"""
Return an iterator to all of the setting value pairs.
"""
class Database(Element):
"""
The interface to an individual database. `Connection` objects inherit from
this
"""
_e_label = 'DATABASE'
@property
@abc.abstractmethod
def backend_id(self) -> (int, None):
"""
The backend's process identifier.
"""
@property
@abc.abstractmethod
def version_info(self) -> tuple:
"""
A version tuple of the database software similar Python's `sys.version_info`.
>>> db.version_info
(8, 1, 3, '', 0)
"""
@property
@abc.abstractmethod
def client_address(self) -> (str, None):
"""
The client address that the server sees. This is obtainable by querying
the ``pg_catalog.pg_stat_activity`` relation.
`None` if unavailable.
"""
@property
@abc.abstractmethod
def client_port(self) -> (int, None):
"""
The client port that the server sees. This is obtainable by querying
the ``pg_catalog.pg_stat_activity`` relation.
`None` if unavailable.
"""
@property
@abc.abstractmethod
def xact(self, isolation = None, mode = None) -> Transaction:
"""
Create a `Transaction` object using the given keyword arguments as its
configuration.
"""
@property
@abc.abstractmethod
def settings(self) -> Settings:
"""
A `Settings` instance bound to the `Database`.
"""
@abc.abstractmethod
def do(language, source) -> None:
"""
Execute a DO statement using the given language and source.
Always returns `None`.
Likely to be a function of Connection.execute.
"""
@abc.abstractmethod
def execute(sql) -> None:
"""
Execute an arbitrary block of SQL. Always returns `None` and raise
an exception on error.
"""
@abc.abstractmethod
def prepare(self, sql : str) -> Statement:
"""
Create a new `Statement` instance bound to the connection
using the given SQL.
>>> s = db.prepare("SELECT 1")
>>> c = s()
>>> c.next()
(1,)
"""
@abc.abstractmethod
def query(self, sql : str, *args) -> Execution:
"""
Prepare and execute the statement, `sql`, with the given arguments.
Equivalent to ``db.prepare(sql)(*args)``.
"""
@abc.abstractmethod
def statement_from_id(self, statement_id) -> Statement:
"""
Create a `Statement` object that was already prepared on the
server. The distinction between this and a regular query is that it
must be explicitly closed if it is no longer desired, and it is
instantiated using the statement identifier as opposed to the SQL
statement itself.
"""
@abc.abstractmethod
def cursor_from_id(self, cursor_id) -> Cursor:
"""
Create a `Cursor` object from the given `cursor_id` that was already
declared on the server.
`Cursor` objects created this way must *not* be closed when the object
is garbage collected. Rather, the user must explicitly close it for
the server resources to be released. This is in contrast to `Cursor`
objects that are created by invoking a `Statement` or a SRF
`StoredProcedure`.
"""
@abc.abstractmethod
def proc(self, procedure_id) -> StoredProcedure:
"""
Create a `StoredProcedure` instance using the given identifier.
The `proc_id` given can be either an ``Oid``, or a ``regprocedure``
that identifies the stored procedure to create the interface for.
>>> p = db.proc('version()')
>>> p()
'PostgreSQL 8.3.0'
>>> qstr = "select oid from pg_proc where proname = 'generate_series'"
>>> db.prepare(qstr).first()
1069
>>> generate_series = db.proc(1069)
>>> list(generate_series(1,5))
[1, 2, 3, 4, 5]
"""
@abc.abstractmethod
def reset(self) -> None:
"""
Reset the connection into it's original state.
Issues a ``RESET ALL`` to the database. If the database supports
removing temporary tables created in the session, then remove them.
Reapply initial configuration settings such as path.
The purpose behind this method is to provide a soft-reconnect method
that re-initializes the connection into its original state. One
obvious use of this would be in a connection pool where the connection
is being recycled.
"""
@abc.abstractmethod
def notify(self, *channels, **channel_and_payload) -> int:
"""
NOTIFY the channels with the given payload.
Equivalent to issuing "NOTIFY <channel>" or "NOTIFY <channel>, <payload>"
for each item in `channels` and `channel_and_payload`. All NOTIFYs issued
*must* occur in the same transaction.
The items in `channels` can either be a string or a tuple. If a string,
no payload is given, but if an item is a `builtins.tuple`, the second item
will be given as the payload. `channels` offers a means to issue NOTIFYs
in guaranteed order.
The items in `channel_and_payload` are all payloaded NOTIFYs where the
keys are the channels and the values are the payloads. Order is undefined.
"""
@abc.abstractmethod
def listen(self, *channels) -> None:
"""
Start listening to the given channels.
Equivalent to issuing "LISTEN <x>" for x in channels.
"""
@abc.abstractmethod
def unlisten(self, *channels) -> None:
"""
Stop listening to the given channels.