PostgreSQL materialized views with Django ¶

My implementation:

import csv
from django.db import models
from django.db import connection
from django.utils import timezone
from django.db import connection
from django.contrib.humanize.templatetags.humanize import intcomma
from ccms_lib.backend.models import CODE_MAX_LENGTH


class SqlViewMixin():

    @classmethod
    def create_view(cls, verbose=False):
        view_name = cls._meta.db_table
        cls_sql = cls.sql().strip()
        if cls_sql.endswith(';'):
            cls_sql = cls_sql[:-1]

        if cls.materialized:
            sql = f"CREATE materialized VIEW IF NOT EXISTS {view_name} AS "
            sql += cls_sql + ';\n'
            pk_name = cls._meta.pk.name
            sql += f'CREATE UNIQUE INDEX IF NOT EXISTS idx_{view_name} ON {view_name}({pk_name});'
        else:
            sql = f"CREATE VIEW {view_name} AS "
            sql += cls_sql + ';\n'
        cls.execute(sql, verbose)

    @classmethod
    def drop_view(cls, verbose=False):
        view_name = cls._meta.db_table
        sql = "DROP %sVIEW IF EXISTS %s CASCADE;\n" % (
            'materialized ' if cls.materialized else '',
            view_name,
        )
        pk_name = cls._meta.pk.name
        sql += f"DROP INDEX IF EXISTS idx_{view_name};"
        cls.execute(sql, verbose)

    @classmethod
    def refresh_view(cls, concurrently=False, verbose=False):
        if cls.materialized:
            #sql = "REFRESH MATERIALIZED VIEW CONCURRENTLY {cls._meta.db_table};"
            sql = "REFRESH MATERIALIZED VIEW %s%s;" % (
                "CONCURRENTLY " if concurrently else '',
                cls._meta.db_table,
            )
            cls.execute(sql, verbose)

    @classmethod
    def execute(cls, sql, verbose):
        with connection.cursor() as cursor:
            if verbose:
                print(sql)
            cursor.execute(sql)

    @classmethod
    def export_view_as_csv(cls, verbose, filename=None, delimiter=','):

        def export_rows(cursor, sql, offset, page_size, writer, verbose):
            if page_size > 0:
                sql = sql + " OFFSET %d LIMIT %d" % (offset, page_size)
            if verbose:
                print(sql)
            cursor.execute(sql)
            if offset <= 0:
                writer.writerow([f.name for f in cursor.description])
            for row in cursor.fetchall():
                writer.writerow(row)

        view_name = cls._meta.db_table

        if filename is None:
            filename = timezone.now().strftime('%Y-%m-%d_%H-%M-%S__') + view_name + '.csv'

        #page_size = 100000 # 0 = no pagination
        page_size = 1000000 # 0 = no pagination
        sql = str(cls.objects.all().query)
        sql += ' ORDER BY "%s"' % cls._meta.pk.name
        n = 0
        step = 0

        if verbose:
            n = cls.objects.count()
            step = int(n / 100)
            print('Exporting file "%s"; records: %s' % (filename, intcomma(n)))

        with open(filename, 'w', newline='') as csvfile:
            writer = csv.writer(csvfile,  dialect='excel', delimiter=delimiter)
            with connection.cursor() as cursor:

                if page_size <= 0:
                    # no pagination
                    cursor.execute(sql)
                    writer.writerow([f.name for f in cursor.description])
                    j = 0
                    row = cursor.fetchone()
                    while row is not None:
                        j += 1
                        if verbose and j==1 or ((j/10) % step) == 0:
                            progress = int((j * 100) / n) + 1
                            print('%d%% (%s/%s)' % (progress, intcomma(j), intcomma(n)))
                        writer.writerow(row)
                        row = cursor.fetchone()

                else:
                    # paginate
                    num_pages = (n // page_size) + (1 if n % page_size else 0)
                    offset = 0
                    j = 0
                    while offset < n:

                        if verbose:
                            progress = int(((j*page_size) * 100) / n)
                            print('page %d/%d (%d%%)' % (j+1, num_pages, progress))

                        export_rows(cursor, sql, offset, page_size, writer, verbose=False)
                        offset += page_size
                        j += 1

################################################################################
# Example ...

class DwhBase(SqlViewMixin, models.Model):

    materialized = True

    id = models.CharField(null=False, max_length=256, primary_key=True)
    base_code = models.CharField(max_length=CODE_MAX_LENGTH, null=False)
    base_name = models.CharField(max_length=256, null=False)

    class Meta:
        managed = False
        db_table = "dwhm_base"

    def __str__(self):
        return str(self.id)

    @staticmethod
    def sql():
        return """
SELECT code AS id,
    code as base_code,
    description AS base_name
   FROM backend_base;
"""

References:

• Using PostgreSQL Views in Django
• Materialized Views for Faster Reads

  django-ninja Notes ¶

from ninja import Router
v1_router = Router(tags=["cclib"])


@v1_router.get("/hello")
def hello(request):
    return "Hello world!"

from typing import List
import uuid
from django.shortcuts import get_object_or_404
from ninja import Router
from ninja import Schema, ModelSchema
from ninja.security import django_auth

from cclib.resources.models import Document

v1_router = Router(tags=["cclib"])


class DocumentSchema(ModelSchema):
    class Meta:
        model = Document
        fields = "__all__"


@v1_router.get("/documents/{uuid:document_id}", response=DocumentSchema, auth=django_auth)
def get_document(request, document_id: uuid.UUID):
    return get_object_or_404(Document, pk=document_id)


@v1_router.get("/documents", response=List[DocumentSchema], auth=django_auth)
def list_documents(request):
    qs = Document.objects.all()
    return qs

import traceback
from typing import List
from ninja import Router
from ninja import Schema, ModelSchema
from ninja.errors import HttpError
from ninja.security import django_auth
from ninja.security import django_auth_superuser
from django.conf import settings
from django.contrib.auth.models import Group
from django.contrib.auth import get_user_model

v1_router = Router(tags=["ccserver"])


class GroupSchema(ModelSchema):
    class Meta:
        model = Group
        fields = "__all__"

class UserSchema(ModelSchema):
    # See: "Nested objects"
    # https://django-ninja.dev/guides/response/#nested-objects
    groups: List[GroupSchema] = []
    class Meta:
        model = get_user_model()
        #fields = "__all__"
        fields = [
            'id',
            'username',
        ]


@v1_router.get("/users", response=List[UserSchema], auth=django_auth_superuser)
def list_users(request):
    try:
        User = get_user_model()
        qs = User.objects.all()
    except Exception as e:
        # See: "Throwing HTTP responses with exceptions"
        # https://django-ninja.dev/guides/errors/#throwing-http-responses-with-exceptions
        raise HttpError(500, str(e) + "\n" + traceback.format_exc())

    return qs

from ninja import NinjaAPI
from ninja.security import django_auth

api = NinjaAPI(csrf=True)

@api.get("/pets", auth=django_auth)
def pets(request):
    return f"Authenticated user {request.auth}"

from ninja.security import HttpBearer


class AuthBearer(HttpBearer):
    def authenticate(self, request, token):
        if token == "supersecret":
            return token


@api.get("/bearer", auth=AuthBearer())
def bearer(request):
    return {"token": request.auth}

from ninja.errors import HttpError

@api.get("/some/resource")
def some_operation(request):
    if True:
        raise HttpError(503, "Service Unavailable. Please retry later.")

  Download a large binary file in chunks with Python ¶

Using requests:

import requests

# https://stackoverflow.com/questions/16694907/download-large-file-in-python-with-requests#16696317
def download_file(url):
    local_filename = url.split('/')[-1]
    # NOTE the stream=True parameter below
    with requests.get(url, stream=True) as r:
        r.raise_for_status()
        with open(local_filename, 'wb') as f:
            for chunk in r.iter_content(chunk_size=8192):
                # If you have chunk encoded response uncomment if
                # and set chunk_size parameter to None.
                #if chunk:
                f.write(chunk)
    return local_filename

Using urlib.request:

import urllib.request

def download_file2(url):
    """
    Use urlib.request instead of requests to avoid "403 Forbidden" errors
    when the remote server tries to prevent scraping (for example when
    is protected behind cloudflare)
    """
    request = urllib.request.Request(url)
    request.add_header('User-Agent', 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:106.0) Gecko/20100101 Firefox/106.0')
    request.add_header('Accept', 'text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8')
    request.add_header('Accept-Language', 'en-US,en;q=0.5')

    response = urllib.request.urlopen(request)
    local_filename = url.split('/')[-1]
    chunk_size = 8192
    with open(local_filename, 'wb') as f:
        size = 0
        while True:
            info = response.read(chunk_size)
            if len(info) < 1:
                break
            size = size + len(info)
            f.write(info)
    return local_filename

  Export Gitlab Issue ¶

#!/usr/bin/env python3
import pprint
import json
import gitlab
import argparse

# Requirements
# python-gitlab==4.11.1

GITLAB_URL = "https://gitlab.brainstorm.it"
GITLAB_PRIVATE_TOKEN = "glpat-******************"
GITLAB_PROJECT = 77
PAGE_BREAK_STRING = '<div style="page-break-after: always;"></div>'


class GitlabClient(gitlab.Gitlab):

    def __init__(self, project_id):
        super().__init__(GITLAB_URL, GITLAB_PRIVATE_TOKEN, order_by='created_at')
        self.project = self.projects.get(project_id)

    def retrieve_issue(self, issue_id):

        issue = self.project.issues.get(issue_id)

        base_url = issue.web_url
        # Es: 'https://gitlab.brainstorm.it/group/project/-/issues/36'
        position = base_url.find('/-/')
        if position >= 0:
            base_url = base_url[:position]
        # Es: 'https://gitlab.brainstorm.it/group/project'

        data = json.loads(issue.to_json())
        self.fix_image_links(data, base_url)
        data['notes'] = []

        notes = issue.notes.list(all=True)
        notes = sorted([n for n in notes if not n.system], key=lambda k: k.created_at)

        for n in notes:
            note = json.loads(n.to_json())
            self.fix_image_links(note, base_url)
            data['notes'].append(note)

        return data

    def fix_image_links(self, data, base_url):
        text = data.get('description', data.get('body'))
        text = text.replace('/uploads/', base_url+'/uploads/')
        if 'description' in data:
            data['description'] = text
        else:
            data['body'] = text

def to_markdown(data):
    text = ""
    for k, v in data.items():

        text += '\n# [%d] %s\n\n' % (k, v['title'])
        text += "### %s (%s)\n\n" % (v['author']['name'], v['created_at'])
        text += "**Link**: %s\n\n" % v['web_url']
        text += v['description']
        text += "\n\n"

        for n in v['notes']:

            text += "\n\n" + (80*'-') + "\n\n"
            text += "### %s (%s)\n\n" % (n['author']['name'], v['created_at'])
            text += n['body']
            text += "\n\n"

        text += "\n\n" + PAGE_BREAK_STRING

    return text


def main():
    parser = argparse.ArgumentParser(description="...")
    parser.add_argument('issue_ids', nargs="+", type=int)
    parser.add_argument("--project_id", "-p", type=int, default=GITLAB_PROJECT, help="Default: %d" % GITLAB_PROJECT)
    parser.add_argument("--format", type=str, choices=["", "markdown", ], default="")
    args = parser.parse_args()

    project_id = args.project_id
    client = GitlabClient(GITLAB_PROJECT)
    data = {}
    for issue_id in args.issue_ids:
        issue_data = client.retrieve_issue(issue_id)
        data[issue_id] = issue_data

    if args.format == 'markdown':
        print(to_markdown(data))
    else:
        pprint.pprint(data)


if __name__ == '__main__':
    main()

  Promises with VanillaJS ¶

.

function print(text) {
    element.textContent = text
}

function returnValueAfterDelay(value, delay) {
    let promise = new Promise(function(resolve, reject) {
        function callback() {
            resolve(value)
        }
        setTimeout(callback, delay);
    })
    return promise
}

function main() {
    returnValueAfterDelay(123, 1000).then(
        function(value) {
            print(value)
        }
    )
}

main()

print = (text) => {
    element.textContent = text
}

let returnValueAfterDelay = (value, delay) => {
    let promise = new Promise((resolve, reject) => {
        let callback = () => resolve(value)
        setTimeout(callback, delay)
    })
    return promise
}

let main = () => {
    returnValueAfterDelay(123, 1000).then(
        (value) => print(value)
    )
}

main()

  Log requests and responses ¶

file main/middleware.py

import logging
from django.utils.deprecation import MiddlewareMixin
from django.conf import settings

logging.basicConfig(level=logging.INFO, format="%(asctime)s:%(levelname)s:%(message)s")


def to_string(value):
    text = str(value)
    nmax = settings.LOG_REQUEST_DETAIL_MAX_LENGTH
    if nmax > 0 and len(text) > nmax:
        text = text[:nmax] + "......"
    return text


def user_ip_address(request):
    x_forwarded_for = request.META.get('HTTP_X_FORWARDED_FOR', None)
    if x_forwarded_for:
        remote_address = x_forwarded_for.split(',')[0].strip()
    else:
        remote_address = request.META.get('REMOTE_ADDR', None)
    return remote_address


class LoggingMiddleware(MiddlewareMixin):
    """
    Log requests and responses

    Adapted from: https://scripting4ever.wordpress.com/2020/07/27/how-to-log-the-request-and-response-via-django-middleware/
    """

    def process_request(self, request):
        if settings.LOG_REQUEST_DETAILS:
            logging.info("=" * 80)
            logging.info(
                "Request Method:        " + to_string(request.META.get("REQUEST_METHOD", "???"))
            )
            logging.info("URL requested:         " + to_string(request.path))
            logging.info("Request Body Contents: " + to_string(request.body))
            logging.info("Request Headers:       " + to_string(request.headers))
            logging.info(
                "Content Length:        " + to_string(request.META.get("CONTENT_LENGTH", "???"))
            )
            logging.info(
                #"Client IP Address:     " + to_string(request.META.get("REMOTE_ADDR", "???"))
                "Client IP Address:     " + to_string(user_ip_address(request))
            )
            logging.info(
                "Host Name of Client:   " + to_string(request.META.get("REMOTE_HOST", "???"))
            )
            logging.info(
                "Host Name or Server:   " + to_string(request.META.get("SERVER_NAME", "???"))
            )
            logging.info(
                "Port of the Server:    " + to_string(request.META.get("SERVER_PORT", "???"))
            )
            logging.info("-" * 80)
        return None

    def process_response(self, request, response):
        if settings.LOG_REQUEST_DETAILS:
            logging.info("Response Content:      " + to_string(response.content))
            logging.info("Response Code:         " + to_string(response.status_code))
            logging.info("Response Headers:      " + to_string(response.headers))
            logging.info("=" * 80)
        return response

then, in settings.py:

MIDDLEWARE = [
    ...
    'main.middleware.LoggingMiddleware',
]

...

LOG_REQUEST_DETAILS = True
LOG_REQUEST_DETAIL_MAX_LENGTH = 200

Adapted from:

• How to log the request and response via Django Middleware?

  dotnet ¶

Example of a simple C# console application that prints "Hello, World!" to the console using top-level statements:

dotnet new console -n HelloWorldApp
cd HelloWorldApp
cat Program.cs

    // Program.cs
    using System;
    Console.WriteLine("Hello, World!");

dotnet run

  Measure writing speed on SSD from command line on Linux ¶

sudo dd if=/dev/zero of=testfile bs=1G count=1 oflag=dsync && sudo rm testfile

  vanillajs fetch() examples ¶

 fetch('https://reqbin.com/echo/get/json', {
     method: 'GET',
     headers: {
         'Accept': 'application/json',
     },
 })
.then(response => response.json())
.then(response => console.log(JSON.stringify(response)))

fetch(
    '/backend/j/mto_evaluate_final_stock_total', {
        method: "post",
        body: data,
        mode: 'cors',   // 'no-cors',
        cache: 'no-cache',
        credentials: 'same-origin',
        headers: {
            // make sure request.is_ajax() return True on the server
            'X-Requested-With': 'XMLHttpRequest',
            'X-CSRFToken': getCookie('csrftoken')
        }
    }
)
.then(function(response) {
    if (response.ok) {
        return response.json()
    }
    // if not 200-OK, reject instead of throw
    // Here, the plan is to get {status: 4XX, message: 'a message'} format as a result in both cases.
    // See: https://stackoverflow.com/questions/38235715/fetch-reject-promise-and-catch-the-error-if-status-is-not-ok#67660773
    return Promise.reject(response)
})
.then(function(data) {
    console.log(data)
    ... use data ...
})
.catch(function(error) {
    // Show error
    console.error(error.status, error.statusText);
    // also get error messages, if any
    // Again, see: https://stackoverflow.com/questions/38235715/fetch-reject-promise-and-catch-the-error-if-status-is-not-ok#67660773
    error.json().then(function(json) {
        console.error(json);
    })
})
.finally(function() {
})

// bind to the form’s submit event
form.addEventListener('submit', function(event) {

    // prevent the form from performing its default submit action
    event.preventDefault();
    header.classList.add('loading');

    // serialize the form’s content and send via an AJAX call
    // using the form’s defined method and action
    let url = form.getAttribute('action') || self.options.url;
    let method = form.getAttribute('method') || 'post';
    // We use FormData // to allow files upload (i.e. process <input type="file"> as expected)
    // Note that, using FormData, we also need (with jQuery):
    // - processData: false
    // - contentType: false
    let data = new FormData(form);
    //console.log('form data: %o', new URLSearchParams(data).toString());

    self._notify('submitting', {method: method, url: url, data:data});

    let promise = fetch(
        self.options.url, {
            method: "post",
            body: data,
            mode: 'cors',   // 'no-cors',
            cache: 'no-cache',
            credentials: 'same-origin',
            headers: {
                // make sure request.is_ajax() return True on the server
                'X-Requested-With': 'XMLHttpRequest',
                'X-CSRFToken': getCookie('csrftoken')
            }
        }
    );
    promise.then(response => {
        if (response.ok) {
            // Upon receiving a JSON response, we assume that the form has been validated,
            // so we can close the modal
            if (response.headers.get('Content-Type') === 'application/json') {
                response.json().then(data => {
                    self._notify('submitted', {method: method, url: url, data: data});
                    self.close();
                })
                .catch(error => {
                    FrontendForms.display_server_error(error);
                })
            }
            else {
                response.text().then(data => {

                    // update the modal body with the new form
                    body.innerHTML = data;

                    // Does the response contain a form ?
                    let form = self.element.querySelector('.dialog-content .dialog-body form');
                    if (form !== null) {
                        // If the server sends back a successful response,
                        // we need to further check the HTML received

                        // If xhr contains any field errors,
                        // the form did not validate successfully,
                        // so we keep it open for further editing
                        //if (jQuery(xhr).find('.has-error').length > 0) {

                        if (form.querySelectorAll('.has-error').length > 0 || form.querySelectorAll('.errorlist').length > 0) {
                            self._notify('loaded', {url: url});
                            self._form_ajax_submit(true);
                        } else {
                            // otherwise, we've done and can close the modal
                            self._notify('submitted', {method: method, url: url, data: data});
                            self.close();
                        }
                    }
                    // If not, assume we received a feedback for the user after successfull submission, so:
                    // - keep the dialog open
                    // - hide the save button
                    else {
                        // We also notify the user about successful submission
                        self._notify('submitted', {method: method, url: url, data: data});
                        btn_save.style.display = 'none';
                    }
                });
            }

        } else {
            self._notify('submission_failure', {method: method, url: url, data: data, error: response.statusText});
            FrontendForms.display_server_error(response.statusText);
        }

    }).catch(error => {
        self._notify('submission_failure', {method: method, url: url, data: data, error:error});
        FrontendForms.display_server_error(error.toString());
    }).finally(() => {
        header.classList.remove('loading');
    });