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
'''