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Build a Simple CRUD App with TiDB and PyMySQL |
Learn how to build a simple CRUD application with TiDB and PyMySQL. |
PyMySQL is a popular open-source driver for Python.
This document describes how to use TiDB and PyMySQL to build a simple CRUD application.
Note:
It is recommended to use Python 3.10 or a later Python version.
The following introduces how to start a TiDB cluster.
Use a TiDB Serverless cluster
For detailed steps, see Create a TiDB Serverless cluster.
Use a local cluster
For detailed steps, see Deploy a local test cluster or Deploy a TiDB cluster using TiUP.
See Create a TiDB Serverless cluster.
git clone https://github.com/pingcap-inc/tidb-example-python.gitThe following uses PyMySQL 1.0.2 as an example. Drivers for Python are more convenient to use than other languages, but they do not shield the underlying implementation and require manual management of transactions. If there are not a lot of scenarios where SQL is required, it is recommended to use ORM, which can help reduce the coupling of your program.
import uuid
from typing import List
import pymysql.cursors
from pymysql import Connection
from pymysql.cursors import DictCursor
def get_connection(autocommit: bool = False) -> Connection:
return pymysql.connect(host='127.0.0.1',
port=4000,
user='root',
password='',
database='test',
cursorclass=DictCursor,
autocommit=autocommit)
def create_player(cursor: DictCursor, player: tuple) -> None:
cursor.execute("INSERT INTO player (id, coins, goods) VALUES (%s, %s, %s)", player)
def get_player(cursor: DictCursor, player_id: str) -> dict:
cursor.execute("SELECT id, coins, goods FROM player WHERE id = %s", (player_id,))
return cursor.fetchone()
def get_players_with_limit(cursor: DictCursor, limit: int) -> tuple:
cursor.execute("SELECT id, coins, goods FROM player LIMIT %s", (limit,))
return cursor.fetchall()
def random_player(amount: int) -> List[tuple]:
players = []
for _ in range(amount):
players.append((uuid.uuid4(), 10000, 10000))
return players
def bulk_create_player(cursor: DictCursor, players: List[tuple]) -> None:
cursor.executemany("INSERT INTO player (id, coins, goods) VALUES (%s, %s, %s)", players)
def get_count(cursor: DictCursor) -> int:
cursor.execute("SELECT count(*) as count FROM player")
return cursor.fetchone()['count']
def trade_check(cursor: DictCursor, sell_id: str, buy_id: str, amount: int, price: int) -> bool:
get_player_with_lock_sql = "SELECT coins, goods FROM player WHERE id = %s FOR UPDATE"
# sell player goods check
cursor.execute(get_player_with_lock_sql, (sell_id,))
seller = cursor.fetchone()
if seller['goods'] < amount:
print(f'sell player {sell_id} goods not enough')
return False
# buy player coins check
cursor.execute(get_player_with_lock_sql, (buy_id,))
buyer = cursor.fetchone()
if buyer['coins'] < price:
print(f'buy player {buy_id} coins not enough')
return False
def trade_update(cursor: DictCursor, sell_id: str, buy_id: str, amount: int, price: int) -> None:
update_player_sql = "UPDATE player set goods = goods + %s, coins = coins + %s WHERE id = %s"
# deduct the goods of seller, and raise his/her the coins
cursor.execute(update_player_sql, (-amount, price, sell_id))
# deduct the coins of buyer, and raise his/her the goods
cursor.execute(update_player_sql, (amount, -price, buy_id))
def trade(connection: Connection, sell_id: str, buy_id: str, amount: int, price: int) -> None:
with connection.cursor() as cursor:
if trade_check(cursor, sell_id, buy_id, amount, price) is False:
connection.rollback()
return
try:
trade_update(cursor, sell_id, buy_id, amount, price)
except Exception as err:
connection.rollback()
print(f'something went wrong: {err}')
else:
connection.commit()
print("trade success")
def simple_example() -> None:
with get_connection(autocommit=True) as connection:
with connection.cursor() as cur:
# create a player, who has a coin and a goods.
create_player(cur, ("test", 1, 1))
# get this player, and print it.
test_player = get_player(cur, "test")
print(test_player)
# create players with bulk inserts.
# insert 1919 players totally, with 114 players per batch.
# each player has a random UUID
player_list = random_player(1919)
for idx in range(0, len(player_list), 114):
bulk_create_player(cur, player_list[idx:idx + 114])
# print the number of players
count = get_count(cur)
print(f'number of players: {count}')
# print 3 players.
three_players = get_players_with_limit(cur, 3)
for player in three_players:
print(player)
def trade_example() -> None:
with get_connection(autocommit=False) as connection:
with connection.cursor() as cur:
# create two players
# player 1: id is "1", has only 100 coins.
# player 2: id is "2", has 114514 coins, and 20 goods.
create_player(cur, ("1", 100, 0))
create_player(cur, ("2", 114514, 20))
connection.commit()
# player 1 wants to buy 10 goods from player 2.
# it will cost 500 coins, but player 1 cannot afford it.
# so this trade will fail, and nobody will lose their coins or goods
trade(connection, sell_id="2", buy_id="1", amount=10, price=500)
# then player 1 has to reduce the incoming quantity to 2.
# this trade will be successful
trade(connection, sell_id="2", buy_id="1", amount=2, price=100)
# let's take a look for player 1 and player 2 currently
with connection.cursor() as cur:
print(get_player(cur, "1"))
print(get_player(cur, "2"))
simple_example()
trade_example()The driver has a lower level of encapsulation than ORM, so there are a lot of SQL statements in the program. Unlike ORM, there is no data object in drivers, so the Player queried by the driver is represented as a dictionary.
For more information about how to use PyMySQL, refer to PyMySQL documentation.
The following content introduces how to run the code step by step.
Before running the code, you need to initialize the table manually. If you are using a local TiDB cluster, you can run the following command:
mysql --host 127.0.0.1 --port 4000 -u root < player_init.sqlmycli --host 127.0.0.1 --port 4000 -u root --no-warn < player_init.sqlIf you are not using a local cluster, or have not installed a MySQL client, connect to your cluster using your preferred method (such as Navicat, DBeaver, or other GUI tools) and run the SQL statements in the player_init.sql file.
If you are using a TiDB Serverless cluster, you need to provide your CA root path and replace <ca_path> in the following examples with your CA path. To get the CA root path on your system, refer to Where is the CA root path on my system?.
If you are using a TiDB Serverless cluster, change the get_connection function in pymysql_example.py:
def get_connection(autocommit: bool = False) -> Connection:
return pymysql.connect(host='127.0.0.1',
port=4000,
user='root',
password='',
database='test',
cursorclass=DictCursor,
autocommit=autocommit)Suppose that the password you set is 123456, and the connection parameters you get from the cluster details page are the following:
- Endpoint:
xxx.tidbcloud.com - Port:
4000 - User:
2aEp24QWEDLqRFs.root
In this case, you can modify the get_connection as follows:
def get_connection(autocommit: bool = False) -> Connection:
return pymysql.connect(host='xxx.tidbcloud.com',
port=4000,
user='2aEp24QWEDLqRFs.root',
password='123546',
database='test',
cursorclass=DictCursor,
autocommit=autocommit,
ssl_ca='<ca_path>',
ssl_verify_cert=True,
ssl_verify_identity=True)Before running the code, use the following command to install dependencies:
pip3 install -r requirement.txtIf you need to run the script multiple times, follow the Table initialization section to initialize the table again before each run.
python3 pymysql_example.py