sqlalchemy how to bind metadata to the table - flask-sqlalchemy

Question

I have tried the solution mentioned in sqlalchemy create tables and also referred to flask documentation http://flask-sqlalchemy.pocoo.org/2.1/contexts/. I am facing problems creating the database tables using create_all(). Here is my code.
>>> from flask import Flask
>>> app = Flask('myflaskapp')
>>> from flask_sqlalchemy import SQLAlchemy
>>> app.url_map.strict_slashes = False
>>> app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql+psycopg2://my_dbuser:my_dbuser_password#localhost/my_dev_db'
>>> app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
>>> from myflaskapp.models import AdRequest, AdResult
>>> AdRequest.__table__
Table('ad_request', MetaData(bind=None), Column('id', Integer(), table=<ad_request>, primary_key=True, nullable=False), Column('status', String(length=10), table=<ad_request>, default=ColumnDefault('NEW')), Column('status_msg', String(length=100), table=<ad_request>, default=ColumnDefault('')), Column('query_str', String(length=100), table=<ad_request>), schema=None)
>>> db = SQLAlchemy(app)
>>> db.engine
Engine(postgresql+psycopg2://my_dbuser:***#localhost/my_dev_db)
>>> db.metadata.create_all(db.engine)
>>> db.engine
Engine(postgresql+psycopg2://my_dbuser:***#localhost/my_dev_db)
>>> db
<SQLAlchemy engine=postgresql+psycopg2://my_dbuser:***#localhost/my_dev_db>
>>> db.session.commit()
On the postgres console a "\dt" does not list the new table ad_request that should get created as a result of running create_all.
Furthermore, I added debug as follows app['SQLALCHEMY_ECHO']=True and I get the following output which I cannot decipher.
>>> app.config['SQLALCHEMY_ECHO']=True
>>> from models import *
>>> with app.app_context():
... db.create_all()
...
2017-07-17 10:24:09,766 INFO sqlalchemy.engine.base.Engine select relname from pg_class c join pg_namespace n on n.oid=c.relnamespace where pg_catalog.pg_table_is_visible(c.oid) and relname=%(name)s
2017-07-17 10:24:09,766 INFO sqlalchemy.engine.base.Engine {'name': 'ad_request'}
2017-07-17 10:24:09,768 INFO sqlalchemy.engine.base.Engine select relname from pg_class c join pg_namespace n on n.oid=c.relnamespace where pg_catalog.pg_table_is_visible(c.oid) and relname=%(name)s
2017-07-17 10:24:09,769 INFO sqlalchemy.engine.base.Engine {'name': 'ad_result'}
2017-07-17 10:24:09,772 INFO sqlalchemy.engine.base.Engine
CREATE TABLE ad_request (
id SERIAL NOT NULL,
status VARCHAR(10),
status_msg VARCHAR(100),
query_str VARCHAR(100),
PRIMARY KEY (id)
)
2017-07-17 10:24:09,772 INFO sqlalchemy.engine.base.Engine {}
2017-07-17 10:24:09,779 INFO sqlalchemy.engine.base.Engine COMMIT
2017-07-17 10:24:09,780 INFO sqlalchemy.engine.base.Engine
CREATE TABLE ad_result (
id SERIAL NOT NULL,
uuid_s VARCHAR(50),
score FLOAT,
ad_request_id INTEGER,
PRIMARY KEY (id),
FOREIGN KEY(ad_request_id) REFERENCES ad_request (id)
)
2017-07-17 10:24:09,780 INFO sqlalchemy.engine.base.Engine {}
2017-07-17 10:24:09,784 INFO sqlalchemy.engine.base.Engine COMMIT
I noticed that AdRequest.table shows Table('ad_request', MetaData(bind=None), ...
How can I make AdRequest bind to the db.metadata ?
Following is my models.py
# models.py
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
db = SQLAlchemy()
ma = Marshmallow()
class AdRequest(db.Model):
id = db.Column(db.Integer, primary_key=True, autoincrement=True)
status = db.Column(db.String(10), default="NEW")
status_msg = db.Column(db.String(100), default="")
query_str = db.Column(db.String(100))
def __init__(self, query_str):
self.query_str = query_str
def __repr__(self):
return '<AdRequest %r, %r, %r, %r>' % (self.id, self.query_str, self.status, self.status_msg)
def as_dict(self):
return {'id': self.id,
'query_str': self.query_str,
'status': self.status,
'status_msg': self.status_msg,
}
class AdResult(db.Model):
id = db.Column(db.Integer, primary_key=True)
uuid_s = db.Column(db.String(50))
score = db.Column(db.Float)
ad_request_id = db.Column(db.Integer, db.ForeignKey('ad_request.id'))
def __init__(self, uuid_s, score, ad_request_id):
self.uuid_s = uuid_s
self.score = score
self.ad_request_id = ad_request_id
def __repr__(self):
return '<AdResult %r, %r, %s>' % (self.id, self.uuid_s, self.ad_request_id)
class AdRequestSchema(ma.Schema):
class Meta:
# Fields to expose
fields = ('id', 'status', 'status_msg', 'query_str')

Answer 1

Order matters when it comes to SQLAlchemy. You have to use the same SQLAlchemy instance when you declare your models and when you use them. In example you provided, you create your database twice - once in models file and once in Python console.
Just create a separate file called database.py with two lines:
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
Then in your models import it and use as base for your models:
from database import db
class AdRequest(db.Model):
id = db.Column(db.Integer, primary_key=True, autoincrement=True)
# rest of your models file
And create your app with:
from flask import Flask
from database import db
from models import AdRequest, AdResult
app = Flask('myflaskapp')
app.url_map.strict_slashes = False
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
with app.app_context():
db.init_app(app) # this is important!
db.create_all()
Please let me know if it helped.
Edit: you can check if my code works by running it and checking out if test.db file was created. If the file is there but you still have your problem, maybe it is PostgreSQL specific issue.