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postgres.py
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postgres.py
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import psycopg2 as pg
from prefect import Task
from prefect.utilities.tasks import defaults_from_attrs
class PostgresExecute(Task):
"""
Task for executing a query against a Postgres database.
Args:
- db_name (str): name of Postgres database
- user (str): user name used to authenticate
- host (str): database host address
- port (int, optional): port used to connect to Postgres database, defaults to 5432 if
not provided
- query (str, optional): query to execute against database
- data (tuple, optional): values to use in query, must be specified using placeholder
is query string
- commit (bool, optional): set to True to commit transaction, defaults to false
- **kwargs (dict, optional): additional keyword arguments to pass to the
Task constructor
"""
def __init__(
self,
db_name: str,
user: str,
host: str,
port: int = 5432,
query: str = None,
data: tuple = None,
commit: bool = False,
**kwargs
):
self.db_name = db_name
self.user = user
self.host = host
self.port = port
self.query = query
self.data = data
self.commit = commit
super().__init__(**kwargs)
@defaults_from_attrs("query", "data", "commit")
def run(
self,
query: str = None,
data: tuple = None,
commit: bool = False,
password: str = None,
):
"""
Task run method. Executes a query against Postgres database.
Args:
- query (str, optional): query to execute against database
- data (tuple, optional): values to use in query, must be specified using
placeholder is query string
- commit (bool, optional): set to True to commit transaction, defaults to false
- password (str): password used to authenticate; should be provided from a `Secret` task
Returns:
- None
Raises:
- ValueError: if query parameter is None or a blank string
- DatabaseError: if exception occurs when executing the query
"""
if not query:
raise ValueError("A query string must be provided")
# connect to database, open cursor
# allow psycopg2 to pass through any exceptions raised
conn = pg.connect(
dbname=self.db_name,
user=self.user,
password=password,
host=self.host,
port=self.port,
)
# try to execute query
# context manager automatically rolls back failed transactions
try:
with conn, conn.cursor() as cursor:
executed = cursor.execute(query=query, vars=data)
if commit:
conn.commit()
else:
conn.rollback()
return executed
# ensure connection is closed
finally:
conn.close()
class PostgresExecuteMany(Task):
"""
Task for executing many queries against a Postgres database.
Args:
- db_name (str): name of Postgres database
- user (str): user name used to authenticate
- host (str): database host address
- port (int, optional): port used to connect to Postgres database, defaults to 5432 if
not provided
- query (str, optional): query to execute against database
is query string
- data (List[tuple], optional): list of values to use in query, must be specified using
placeholder
- commit (bool, optional): set to True to commit transaction, defaults to false
- **kwargs (dict, optional): additional keyword arguments to pass to the
Task constructor
"""
def __init__(
self,
db_name: str,
user: str,
host: str,
port: int = 5432,
query: str = None,
data: list = None,
commit: bool = False,
**kwargs
):
self.db_name = db_name
self.user = user
self.host = host
self.port = port
self.query = query
self.data = data
self.commit = commit
super().__init__(**kwargs)
@defaults_from_attrs("query", "data", "commit")
def run(
self,
query: str = None,
data: list = None,
commit: bool = False,
password: str = None,
):
"""
Task run method. Executes many queries against Postgres database.
Args:
- query (str, optional): query to execute against database
- data (List[tuple], optional): list of values to use in query, must be specified using
placeholder
- commit (bool, optional): set to True to commit transaction, defaults to false
- password (str): password used to authenticate; should be provided from a `Secret` task
Returns:
- None
Raises:
- ValueError: if query parameter is None or a blank string
- DatabaseError: if exception occurs when executing the query
"""
if not query:
raise ValueError("A query string must be provided")
if not data:
raise ValueError("A data list must be provided")
# connect to database, open cursor
# allow psycopg2 to pass through any exceptions raised
conn = pg.connect(
dbname=self.db_name,
user=self.user,
password=password,
host=self.host,
port=self.port,
)
# try to execute query
# context manager automatically rolls back failed transactions
try:
with conn, conn.cursor() as cursor:
executed = cursor.executemany(query=query, vars_list=data)
if commit:
conn.commit()
else:
conn.rollback()
return executed
# ensure connection is closed
finally:
conn.close()
class PostgresFetch(Task):
"""
Task for fetching results of query from Postgres database.
Args:
- db_name (str): name of Postgres database
- user (str): user name used to authenticate
- host (str): database host address
- port (int, optional): port used to connect to Postgres database, defaults to 5432 if
not provided
- fetch (str, optional): one of "one" "many" or "all", used to determine how many
results to fetch from executed query
- fetch_count (int, optional): if fetch = 'many', determines the number of results to
fetch, defaults to 10
- query (str, optional): query to execute against database
- data (tuple, optional): values to use in query, must be specified using placeholder
is query string
- commit (bool, optional): set to True to commit transaction, defaults to false
- **kwargs (dict, optional): additional keyword arguments to pass to the
Task constructor
"""
def __init__(
self,
db_name: str,
user: str,
host: str,
port: int = 5432,
fetch: str = "one",
fetch_count: int = 10,
query: str = None,
data: tuple = None,
commit: bool = False,
**kwargs
):
self.db_name = db_name
self.user = user
self.host = host
self.port = port
self.fetch = fetch
self.fetch_count = fetch_count
self.query = query
self.data = data
self.commit = commit
super().__init__(**kwargs)
@defaults_from_attrs("fetch", "fetch_count", "query", "data", "commit")
def run(
self,
fetch: str = "one",
fetch_count: int = 10,
query: str = None,
data: tuple = None,
commit: bool = False,
password: str = None,
):
"""
Task run method. Executes a query against Postgres database and fetches results.
Args:
- fetch (str, optional): one of "one" "many" or "all", used to determine how many
results to fetch from executed query
- fetch_count (int, optional): if fetch = 'many', determines the number of results
to fetch, defaults to 10
- query (str, optional): query to execute against database
- data (tuple, optional): values to use in query, must be specified using
placeholder is query string
- commit (bool, optional): set to True to commit transaction, defaults to false
- password (str): password used to authenticate; should be provided from a `Secret` task
Returns:
- records (tuple or list of tuples): records from provided query
Raises:
- ValueError: if query parameter is None or a blank string
- DatabaseError: if exception occurs when executing the query
"""
if not query:
raise ValueError("A query string must be provided")
if fetch not in {"one", "many", "all"}:
raise ValueError(
"The 'fetch' parameter must be one of the following - ('one', 'many', 'all')"
)
# connect to database, open cursor
# allow psycopg2 to pass through any exceptions raised
conn = pg.connect(
dbname=self.db_name,
user=self.user,
password=password,
host=self.host,
port=self.port,
)
# try to execute query
# context manager automatically rolls back failed transactions
try:
with conn, conn.cursor() as cursor:
cursor.execute(query=query, vars=data)
# fetch results
if fetch == "all":
records = cursor.fetchall()
elif fetch == "many":
records = cursor.fetchmany(fetch_count)
else:
records = cursor.fetchone()
if commit:
conn.commit()
return records
# ensure connection is closed
finally:
conn.close()