Showing posts from 2018

SQLAlchemy (Flask) count model instances by unique values

One comes to a task that has to do with counting items in a database. We will describe the right approach here. Despite being so obvious I did not find much of the docs for junior developers to watch and learn. Here is a sample task and solution:
Let's assume we have a model like so:
classCycle(db.Model):id=db.Column(db.Integer,primary_key=True)object_id=db.Column(db.String,nullable=False) Sample date populated into it will be:
{id:1,object_id:'unique1'},{id:2,object_id:'unique1'},{id:3,object_id:'unique2'},{id:4,object_id:'unique2'},{id:5,object_id:'unique2'},{id:6,object_id:'unique3'} We need to count unique model instances with same object_id. To achieve this relatively simple task one would go straightforward. E.g. Fetch all the Cycle instances with a simple query and then iterate through them via for cycle. Looks like so:

PostgreSQL DB with pgAdmin4 access through SSH tunnel

Despite using console most of the time I have a preference to edit PostgreSQL databases through UI. Especially when it comes to remote side. Usually one can access this through $ psql command. However this tends to writing raw SQL queries and a lot of typing in overall.
Here is a way to do it with UI. First one needs to make a tunnel.Command is fairly simple:
ssh -fNg -L 5555:localhost:5432{username}@{} One has a tunnel afterwards. This command opens a SSH connection in the background mapping your local port 5555 to your server’s port 5432 (Postgres’ default port). To understand one can observe the meaning of the flags via $ man ssh to see what each of these flags doing.
 It can be accessed via localhost tools like pgAdmin4 at localhost and port 5555
DB config would look like so:

Run Flask with Debug in PyCharm

I have gotten to setting UP a Flask environment for a project recently. Was completely puzzled by how to run this. I have used to running Django project with python script. This means pointing out a PyCharm interpreter into a certain point of entry, that is also a .py file also.

In flask way of starting things there is another approach however. Here it is in Flask Docs.
It states to set a variable FLASK_APP and then run a flask run command. This will confuse running a python script way of a project being run. Thus to fix this one needs to set a path to flask binary file. It usually is within a virtual environment binary directory, place where your python interpreter resides.

So to set debugging one needs to set path to script binary one needs:
Script: /path/to/env/bin/flaskScript parameters: runEnvironment variable FLASK_APP=app.pyEnvironment variable FLASK_DEBUG=TrueSet working directory back to your app path (It changes automatically according to script being set) So my wil…

Promise -fication of JS calls.

Found a new pattern to use recently that is called Promise. I really like the way ES6/7 brings new thinking patterns into life nowdays. Here is Promise used instead of old pattern.

It was to give JS method a callback function. This splitting code and making a lot of possibilities for error to come out in this place.

One would write old times according to MDN:
functiongreeting(name){alert('Hello '+name);}functionprocessUserInput(callback){varname=prompt('Please enter your name.');callback(name);}processUserInput(greeting); And now it is made with Promise pattern like so:
letpromise=newPromise((resolve,reject)=>{resolve(prompt('Please enter your name.'));});promise.then((name)=>{alert('Hello '+name);}); In general and briefly this now helps to avoid 'callback hell' with functions passed as arguments and write asynchronous code a sort of in synchronous manner.

This all becomes extra useful upon one having need to load set of data from a differe…