Flask API learning path

Before You Start

Microblog is the comment panel on OCS pages, and a Flask API runs it. In this lesson you use it first, then read the code behind it, then show its posts on a page of your own. If you built the Spring feature in Backend Fullstack Development, you will see the same five parts arranged differently.

Popcorn Hack 1: Post and Watch the Request

Send a real request before reading any code.

  1. Open your browser’s developer tools, choose the Network tab, and filter by microblog.
  2. Press Microblog at the top of this page. If you are not signed in, use Guest Signup in the panel.
  3. Post one sentence: what should an API check before it saves a post? Posts are public, so leave out anything personal.
  4. Select the POST request in the Network tab. Find the URL, the content and topicPath you sent, the status code, and the id that came back.

Keep that request open. The rest of this lesson explains what happened to it.

Read Posts with REST Client

Use the Flask backend’s local REST Client environment and authenticate with api/user_auth.http, as in the User API lesson. Keep the same host so the authentication cookie is reused. Add these requests to an .http file inside that backend repository and send them independently.

### Authenticated read - expect an object with microblogs and count
GET {{baseUrl}}/api/microblog?limit=5
Accept: application/json

### Authenticated validation check - expect 400 and no new post
POST {{baseUrl}}/api/microblog
Content-Type: application/json
Accept: application/json

{
  "content": ""
}

After successful authentication, the empty-content request returns Content is required. If authentication fails first, the content-validation path has not been tested. These are manual checks, not automated assertions; inspect both the status and message.

Read api/microblog_api.py

Find the /api blueprint prefix and the /microblog registration for MicroBlogAPI._CRUD. Read token_required() before the CRUD methods. This API is more than a list endpoint: its handler validates input, selects model calls, checks permissions, and constructs a response.

Method Read for These Decisions
GET limit, search, topicId, pagePath, and userId select a retrieval path; the response contains microblogs and count.
POST content is required and limited to 280 characters; topicId, topicPath, and data are optional.
PUT An id is required; the post must exist, and the caller must own it or have Admin permissions.
DELETE An id is required; existence and ownership/Admin checks precede deletion.

Read the order of the GET branches. Multiple filters do not automatically mean all filters are combined: identify which branch wins from the code. Read each method’s actual status codes rather than importing assumptions from another API.

Follow model/microblog.py

Follow one retrieval branch into MicroBlog.search_content, get_by_topic, get_by_user, or get_all. For the page-path branch, identify the lookup in Topic before the post retrieval call.

Read the create handler with your Popcorn Hack 1 request beside it: optional topicPath can trigger Topic.get_or_create_for_page, then a MicroBlog instance is created and its model methods produce response data. Identify the inputs and returned values at each boundary.

That is the model scope of this lesson. Table design, joins, relationships, SQLAlchemy queries, and migrations belong in a separate database series. Beyond your one post in the panel, actual writes should use disposable, authorized development records with a cleanup plan; they are not required for the read and validation checks above.

Popcorn Hack 2: Match the Spring Parts

The Spring feature splits its work across five files. Microblog does the same jobs in fewer places.

Spring Part Its Job Where Microblog Does It
Entity Describes the table MicroBlog class with db.Column fields in model/microblog.py
JPA Repository Reads and saves rows Methods on the same class, such as get_by_topic, search_content, and create
Service Holds the rules No separate file: rules sit in the handler, such as the Content is required check
Controller Turns HTTP into method calls MicroBlogAPI._CRUD in api/microblog_api.py
Table Initializer Makes sure the table exists db.create_all() in the backend’s database scripts builds tables from the models

Answer these in the Microblog panel on this page:

  1. The 280 character limit appears in two places. Find len(content) > 280 in the handler and db.String(280) in the model. What does each one protect?
  2. put checks that the caller owns the post. Which Spring file would hold that check?

Popcorn Hack 3: Show Posts with UI Builder

UI Builder never sends sign-in cookies, so GET /api/microblog will not work there: it needs token_required(). Find TopicAPI._PageMicroblogs in api/microblog_api.py. Its get has no token_required(), but it still checks the topic first:

Response Reason
200 The topic exists and allows anonymous viewers
401 The topic does not allow anonymous viewers and nobody is signed in
404 No topic has this key yet

Your Popcorn Hack 1 post sent a topicPath, so the create handler made this page’s topic with allow_anonymous=True. Topic._generate_page_key then turned /python/flask/api/microblog into the key python_flask_api_microblog.

  1. Sign in, open UI Builder, and start from the Flask API starter template.
  2. In Data from your API, change the link to https://flask.opencodingsociety.com/api/microblog/page/python_flask_api_microblog and press Test connection. A 404 means nobody has posted on this page yet.
  3. Read the warning about userUid. This route is public, so everyone can read what it returns, and a response should only carry fields a stranger may see.
  4. Choose how to show the posts, then press Code to read the ocs__ classes behind your page.

These are manual checks, so inspect the status and the posts yourself.

Continue by Reading the Repository

Choose a reply, reaction, or topic resource in this same source file. Apply the routine from the API hub: registered URL, handler, permissions, input validation, model call, and response.

After Jokes, Users, and Microblog, the Flask source code is the API learning reference. Use your existing project discussion to explain your trace and compare the contract with the observed response, rather than looking for another standalone API tutorial.

Study This With AI

Paste api/microblog_api.py and model/microblog.py into your AI tool, then check its answers against the code. Never paste passwords, tokens, or your .env file.

  • Draw it: Draw a Mermaid sequence diagram of one POST to /api/microblog, from the browser through the handler and model to the database and back.
  • Quiz me: Ask me 5 questions, one at a time, on which GET branch wins when a request sends more than one filter. Tell me what I missed.
  • Compare it: Show where a Spring service would hold the rules in this handler, and what Flask gains and loses by keeping them there.
  • Break it: List 3 requests that would fail on this API and the status code each returns. I will test them in my .http file and tell you where you were wrong.