Query an existing mysql table in database using flask-sqlalchemy

Question

I have an flask app, using flask-slqalchemy to query a mysql database

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:password@localhost/abc'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
db = SQLAlchemy(app)

there is a table "users" in "abc" database and it is already populated with several hundred rows. Now i need to import this existing table, rather than first defining it with db.Model how do i call the table? if i do this

from sqlalchemy import Table
USERS = Table('users', db.metadata,autoload=True, autoload_with=db.engine)

then i am not able to make a query like

USERS.query.filter_by(done=1).with_entities(USERS.name,USERS.country).paginate(page, 15, False)

it generates an error

AttributeError: 'Table' object has no attribute 'query'

because this is sqlchemy command, not flask-sqlchemy, i dont fully understand this.

I have to first define the table USERS like i am creating it for the first time :

class USERS(db.Model):
 __tablename__ = 'users'
 id = db.Column(db.Integer, primary_key=True, autoincrement=True)
 name = db.Column(db.VARCHAR(500))
 country = db.Column(db.VARCHAR(50))
 def __init__(self, id, name, country):
 self.id = id
 self.name = name
 self.country = country
 def __repr__(self):
 return self.id

only then i am able to use USERS to query the database through flask-sqlalchemy

How do i access the an existing table users using flask-sqlchemy in an flask app?

Answer 1

In sqlalchemy you should query table(s) with session if you want to query Table(). Because 'Table' object has no attribute 'query'. And you do not need to create table if it has existed, just use it. sqlalchemy existing database query

from sqlalchemy import Table, Column, String, create_engine, MetaData
from sqlalchemy.orm import sessionmaker
engine = create_engine()
metadata = MetaData()
test_ = Table('test', metadata,
 Column('msg', String, primary_key=True),
 Column('msg_', String)
)
Session = sessionmaker(bind=engine)
session = Session()
print(session.query(test_).filter_by(msg_ = "test").with_entities("msg","msg_").one())
# ('t', 'test')

In flask_sqlalchemy, it almost same as sqlalchemy did.

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = ""
db = SQLAlchemy(app)
class test(db.Model):
 msg = db.Column(db.String, primary_key=True)
 msg_ = db.Column(db.String)
 def __init__(self, msg, msg_):
 self.msg = msg
 self.msg_ = msg_
 def __repr__(self):
 return "msg: {} msg_: {}".format(self.msg,self.msg_)
result = test.query.filter_by(msg_="test").one()
print(result)
print(result.msg,result.msg_)
'''
msg: t msg_: test
t test
'''

• Aarushi: i am using flask_sqlalchemy, so i have to define the table and list all its columns and rather than using any binding statement, it will bind it own its own?
• KC.: Yes, if you are using class-base. You can try to list part of columns then the error will be raised. And __init__ is not necessary unless you want to override the constructor(ref).