I am working on a program to store my picture meta data and thumbnails into a postgres database using python and psycopg2. In the example I have defined a class MyDbase with methods to create a table, store a value and load a value. Each of these methods needs to connect to the database and a cursor object to execute sql commands. To avoid repetition of code to make the connection and get the cursor I have made a sub class DbDecorators with a decorator connect.
My question: is this a proper way to handle this and specifically using the with statement and passing the cursor to the Dbase method (func) inside the wrapper?
from functools import wraps
import psycopg2
class MyDbase:
''' example using a decorator to connect to a dbase
'''
table_name = 'my_table'
class DbDecorators:
host = 'localhost'
db_user = 'db_tester'
db_user_pw = 'db_tester_pw'
database = 'my_database'
#classmethod
def connect(cls, func):
#wraps(func)
def wrapper(*args, **kwargs):
connect_string = f'host=\'{cls.host}\' dbname=\'{cls.database}\''\
f'user=\'{cls.db_user}\' password=\'{cls.db_user_pw}\''
result = None
try:
with psycopg2.connect(connect_string) as connection:
cursor = connection.cursor()
result = func(*args, cursor, **kwargs)
except psycopg2.Error as error:
print(f'error while connect to PostgreSQL {cls.database}: '
f'{error}')
finally:
if connection:
cursor.close()
connection.close()
print(f'PostgreSQL connection to {cls.database} is closed')
return result
return wrapper
#staticmethod
def get_cursor(cursor):
if cursor:
return cursor
else:
print(f'no connection to database')
raise()
#classmethod
#DbDecorators.connect
def create_table(cls, *args):
cursor = cls.DbDecorators().get_cursor(*args)
sql_string = f'CREATE TABLE {cls.table_name} '\
f'(id SERIAL PRIMARY KEY, name VARCHAR(30));'
print(sql_string)
cursor.execute(sql_string)
#classmethod
#DbDecorators.connect
def store_value(cls, name, *args):
cursor = cls.DbDecorators().get_cursor(*args)
sql_string = f'INSERT INTO {cls.table_name} (name) VALUES (%s);'
print(sql_string)
cursor.execute(sql_string, (name,))
#classmethod
#DbDecorators.connect
def load_value(cls, _id, *args):
cursor = cls.DbDecorators().get_cursor(*args)
sql_string = f'SELECT * FROM {cls.table_name} where id = \'{_id}\';'
print(sql_string)
cursor.execute(sql_string)
db_row = cursor.fetchone()
return db_row
def test():
my_db = MyDbase()
my_db.create_table()
my_db.store_value('John Dean')
db_row = my_db.load_value(1)
print(f'id: {db_row[0]}, name: {db_row[1]}')
if __name__ == '__main__':
test()
probably I did not get your request correctly. Why you need decorator but don't use context manager? Like define db client in any file where from you can import it later and then use it in context manager –
from psycopg2 import SomeDataBase
db = SomeDataBase(credentials)
def create_table(table_name):
with db:
sql_string = f'CREATE TABLE {table_name} '\
f'(id SERIAL PRIMARY KEY, name VARCHAR(30));'
db.cursor.execute(sql_string)
Using a context manager will not close the connection, only the cursor. So using the decorator pattern actually makes more sense here. More info on the context manager: https://www.psycopg.org/docs/usage.html (scroll down to the "with statement" section.)
Related
I'm trying to figure out how I can simply check that the execute_db returns
a method call with the name cursor.fetchone?
I'm not interested to see if the db works, that will be done in a integration test later on.
I've written a small unittest already, but here I'm only mocking the return value.. I want to find a way to test that the method with the given name is being called as well.
class DataChecker:
def __init__(self):
# Initialize class
self.conn = sqlite3.connect("pos.db")
self.cursor = self.conn.cursor()
def execute_db(self, query, params=None):
# Execute SQL query with parameters and return data
self.cursor.execute(query, [params])
self.conn.commit()
return self.cursor.fetchone()
Test:
def test_execute_db():
mock_datachecker = Mock()
mock_datachecker.cursor.fetchone.return_value = "one"
assert DataChecker.execute_db(mock_datachecker, "SELECT * FROM Customers;", 1) == "one"
You would mock the method fetchone from sqlite3 that is imported in DataChecker module.
db.py
import sqlite3
class DataChecker:
def __init__(self):
# Initialize class
self.conn = sqlite3.connect("pos.db")
self.cursor = self.conn.cursor()
def execute_db(self, query, params=None):
# Execute SQL query with parameters and return data
if params:
self.cursor.execute(query, params)
else:
self.cursor.execute(query)
self.conn.commit()
return self.cursor.fetchone()
Then you could use the db.sqlite3 to mock the connect().cursor().fetchone method.
def test_execute_db():
with patch('db.sqlite3') as mock_db:
mock_db.connect().cursor().fetchone.return_value = "one"
assert DataChecker().execute_db("SELECT * FROM Customers") == "one"
I need help with this program. I am making a program for a library in Python 3 (psycopg2) and I am making my modules to handle my tables, I have already done the "create" module and I am doing the "delete" module, I need help to do it, the code used is the following:
This is my class ConnectioDB: (it works to connect to my database in postgresql)
class ConnectionDB:
"""Connection class."""
bd = None
cursor = None
def __init__(self, **param):
"""Connection constructor."""
try:
self.db = connect(
host = '127.0.0.1', # localhost
user = 'postgres'
password = #$#!#*
database = 'national-library'
)
self.cursor = self.db.cursor()
except Error as e:
write_errors(e, 'Failed to connect to database')
with the following lines are used to execute sql code:
def execute_sql(
self,
sentence_sql,
param=None,
write_in_db=True
):
"""Execute SQL code."""
try:
execute = self.cursor.execute(sentence_sql, param)
if write_in_db:
result = self.db.commit()
except Exception as e:
write_errors(e, f"An error occurred while executing the SQL statement:\n\n{sentence_sql}\n")
if write_in_db:
self.db.rollback()
now this is my Model class that has the "create" module
class Model():
"""Generic model class."""
table_name = None
connection = ConnectionDB()
def create(self):
"""Save in database."""
table_name = self.table_name
keys = ", ".join(self.__dict__.keys())
values_placeholders = ", ".join(["%s" for i in range(len(self.__dict__.keys()))])
values = self.__dict__.values()
sql = f"INSERT INTO {table_name} ({keys}) VALUES ({values_placeholders})"
self.connection.execute_sql(sql, tuple(values))
I was trying to do the following code for my "delete" module but I'm not sure if it's ok:
def delete(self, column_id):
"""Delete an item in the database."""
table_name = self.table_name
sql = f"DELETE FROM {table_name} WHERE id = %s"
self.connection.execute_sql(sql, (column_id, ))
I hope you can help me. Thank you!
For a hobby project I'm doing at the moment I want to write an object oriented python program.But one of the first issue I'm running into is creating a class for my (MySQL) database.
I am trying to use as few packages as possible and I want to try to write the database class by using only pymysql.The problem is that there is an overwhelming amount of libraries and a lack of explanation on writing a good database class in python.
Any suggestions and especially examples would be much appreciated
When having the exact same situation, I found the mysql-connector-python class with which I created a small "model" to call from other classes. This is a cut-down version which shows various db calls. As you can see I have a config class which holds all db authentication info and more).
# dependancy: mysql-connector-python (https://dev.mysql.com/downloads/connector/python/2.1.html)
import mysql.connector
import time
import config
import HTMLParser
import StringIO
html_parser = HTMLParser.HTMLParser()
try:
connection = mysql.connector.connect( user=config.DB_USER, password=config.DB_PASSWORD,
host = config.DB_HOST, database=config.DB_DATABASE, unix_socket=config.UNIX_SOCKET)
cursor = connection.cursor()
except mysql.connector.Error as err:
logger.log('Database connection failed for '+config.DB_USER+'#'+config.DB_HOST+'/'+config.DB_DATABASE)
exit()
def get_bad_words():
sql = ("SELECT word FROM word_blacklist")
results = execute(sql)
return results
def get_moderation_method():
sql = ("SELECT var_value FROM settings "
"WHERE var_key = %(key)s")
results = execute(sql, True, {'key':'moderation_method'})
return results[0]
def current_events():
sql = ("SELECT count(id) FROM events WHERE event_date >= DATE_SUB(NOW(), INTERVAL 2 hour) AND event_date <= DATE_ADD(NOW(), INTERVAL 5 hour)")
results = execute(sql, True)
return results[0]
def insert_social_post(channel, filter_type, post_id, validate, user_name, user_id, user_profile_picture, text, post_date, image_url, state):
try:
san_user_name = html_parser.unescape(user_name.encode('utf-8').strip()).decode("utf8").encode('ascii','ignore')
except:
san_user_name = html_parser.unescape(user_name.strip())
try:
san_text = html_parser.unescape(text.encode('utf-8').strip()).decode("utf8").encode('ascii','ignore')
except:
san_text = html_parser.unescape(text.strip())
insert_post = ("INSERT IGNORE INTO social_posts "
"(channel, filter_type, post_id, validate, user_name, user_id, user_profile_picture, text, post_date, image_url, state)"
"VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s, %s, %s)")
execute(insert_post, False, [channel, filter_type, str(post_id), validate,
san_user_name.strip(), user_id, user_profile_picture, san_text.strip(), post_date, image_url, state], True)
def delete_posts(ids):
fmt = ','.join(['%s'] * len(ids))
cursor.execute("DELETE FROM `social_posts` WHERE id IN (%s)" % fmt,
tuple(ids))
connection.commit()
def update_campaigns(campaigns):
sql = ("UPDATE social_campaigns "
"SET last_updated = NOW()"
"WHERE id IN ("+(','.join(str(c) for c in campaigns))+")")
execute(sql, False, None, True)
def execute(tuple, single = False, args = {}, commit = False):
cursor.execute(tuple, args)
if commit == True:
connection.commit()
else:
if single == True:
return cursor.fetchone()
else:
return cursor.fetchall()
def lastrowid():
return cursor.lastrowid
def close():
connection.close()
Call upon the class like this:
import db
bad_words = db.get_bad_words()
import sqlite3
"""singleton class to deal with db"""
'''same can be use for pymysql just replace the sqlite3 with pymysql'''
class DBConnection:
instance = None
def __new__(cls, *args, **kwargs):
if cls.instance is None:
cls.instance = super().__new__(DBConnection)
return cls.instance
return cls.instance
def __init__(self, db_name='you-db-name'):
self.name = db_name
# connect takes url, dbname, user-id, password
self.conn = self.connect(db_name)
self.cursor = self.conn.cursor()
def connect(self):
try:
return sqlite3.connect(self.name)
except sqlite3.Error as e:
pass
def __del__(self):
self.cursor.close()
self.conn.close()
# write your function here for CRUD operations
This is my first time using sqlite3 through class inheritance, and I've run into a problem where I get no traceback errors, but the queries I execute won't commit. I simplified my code
import sqlite3 as lite
class BaseModel(lite.Connection):
def __init__(self, **args):
lite.Connection.__init__(self, **args)
self.cur = self.cursor()
def execute(self, query):
self.cur.execute(query)
class Model(BaseModel):
def __init__(self, **args):
BaseModel.__init__(self, **args)
def _new_(self):
queries = []
queries.append(' '.join(['CREATE TABLE IF NOT EXISTS tb1',
'(id INTEGER PRIMARY KEY,',
'column1 TEXT,',
'column2 INT)']))
for q in queries:
self.execute(q) # execute the queries
self.commit() # write changes to db
def tables(self):
query = 'SELECT name FROM sqlite_master WHERE type="table" ORDER BY name'
results = self.execute(query)
return results#.fetchall()
if __name__ == '__main__':
model = Model(database='test.db')
model._new_()
# Test Fails because the queries aren't being saved in the db
# see Model.__new__ for details
tables = model.tables() # get all tables
print 'Tables Created:'
if tables:
for t in model.tables():
print '\t%s' % str(t[0])
else: print tables
You need to call self.commit():
self.commit() # write changes to db
Without the () you are merely referencing the method, not invoking it.
Next, your execute() function doesn't return anything:
def execute(self, query):
return self.cur.execute(query)
I am new to Python and can't seem to figure out why the .getRow method doesn't run. I created a DBMain class in dbMain.py and I am using pyTest.py to create the DBMain object to run getRow. When I run the debugger in Eclipse and DBMain's constructor does run but but when the getRow method is call nothing happens.
pyTest.py
import dbMain
def main():
db = dbMain.DbMain()
db.getRow()
if __name__ == '__main__':
main()
dbMain.py
##PydevCodeAnalysisIgnore
import pyodbc
class DbMain(object):
cncx = ''
def __init__(self):
cnxn = pyodbc.connect(driver='{SQL Server}',
server='server',
database='database',
uid='name',
pwd='pwd')
def getRow():
cursor = cnxn.cursor()
cursor.execute("select user_id, user_name from users")
row = cursor.fetchone()
return row
You do not return anything from getRow. Maybe you want to include something like
...
return row
Your getRow() method is not bound to the class. The signature for an instance method should look something like getRow(self) - the first parameter is the instance, which is received explicitly (but passed implicitly, when you call someinstance.method()).
To have something functional, you maybe should alter your dbMain to something like this:
##PydevCodeAnalysisIgnore
import pyodbc
class DbMain(object):
def __init__(self):
# make cnxn an attribute of the instance
self.cnxn = pyodbc.connect(driver='{SQL Server}', server='server',
database='database', uid='name', pwd='pwd')
# receive `self` explicitly
def getRow(self):
cursor = self.cnxn.cursor()
cursor.execute("select user_id, user_name from users")
row = cursor.fetchone()
# actually return something
return row
Further reading:
Python: Difference between class and instance attributes