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?

KC. KC. · Accepted Answer · 2018-12-10T08:23:22

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
'''

Query an existing mysql table in database using flask-sqlalchemy

1 Answers