How to read data from postgresql in python using Flask and SQLAlchemy?

Question

I started creating a flask application as I will be needing to do some visualization of some data that was recently transferred to a local postgresql database.

I have a lot of tables (33) which all have the same kind of content as currently just works as containers for different types of data (They contain a JSON object that's different in each of the tables though).

The tables are named "Table_#" (where # symbolizes a number among a defined subset of numbers).

models.py

I have created the following model:

from sqlalchemy import BigInteger, Column, JSON, Text
from app import db

class Table_1(db.Model):
    __tablename__ = 'table_1'

    id = db.Column(BigInteger, primary_key=True)
    did = db.Column(Text)
    timestamp = db.Column(BigInteger)
    data = db.Column(JSON)
    db_timestamp = db.Column(BigInteger)

    def __repr__(self):
        return '<1_Data %r>' % (self.did)

to test if I can actually grab some data from my postgresql.

__init__.py

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config.from_object('config')
db = SQLAlchemy(app)

from app import views, models

config.py

In my config.py I have the following:

SQLALCHEMY_DATABASE_URI = "postgresql://<username>:<password>@localhost:5432/backupdata" //Ofc <username> and <password> isn't my credentials..

In my terminal (Windows cmd) I've tried running the following:

>python
>>>from app import db, models
>>>row = models.Table_1.query.get(1)

But for some reason when I try to print my row nothing is output.

I was hoping someone could have an idea why that is?

Answer 1

I updated my model a bit, to see that I actually got a specific row.

from sqlalchemy import BigInteger, Column, JSON, Text
from app import db

class Table_1(db.Model):
    __tablename__ = 'table_1'

    id = db.Column(BigInteger, primary_key=True)
    did = db.Column(Text)
    timestamp = db.Column(BigInteger)
    data = db.Column(JSON)
    db_timestamp = db.Column(BigInteger)

    def __repr__(self):
        return '<1_Data %r, %r>' % (self.did, self.id)

And then the following query made me aware that actually have a working connection to SQLAlchemy through my flask application.

row = models.Table_910.query.filter_by(did='357139052424715').first()

Knowing that I have one item with the above did I could get a single item:

<1_Data '357139052424715', 738390911>

Answer 2

As stated in your answer, you would need to use the firts() method. Another option would be to limit your query as follows:

Table.query.limit(1).all()

This way you don't need a filter and can just retrieve the first item in the query (which seems to be what you wanted to do originally with query.get(1)

See here for more info.

Answer 3

This sloution is with postgres and Flask without SQLAlchemy

@app.route('/contextget', methods=['GET']) 
def contextget():
    sql_query ="""SELECT * FROM context"""
    out = cur.execute(sql_query)
    context_records = cur.fetchall() 
    ContextRootKeys = []
    outp ="Print each row and it's columns values"
    for row in context_records:
        ContextRootKeys.append(row[1])
    conn.commit()
    print(ContextRootKeys)
    return outp