Connecting Requests to JSON Storage

The guided application called a supplied addition operation. To understand how that operation preserves records, first distinguish the values belonging to one request, the running Python program, and a saved file.

Requests and a Running Program

A new request calls a route again within the running Python program. Different browser tabs reach that same program and its current data. Each call has its own arguments and context, while a module-level list can remain available between calls. Filtering produces a selected view; it leaves that source list unchanged.

The next question uses a memory-only application. Follow the list across requests and a restart.

task_titles = ["Read the article", "Practise loops"]

def matching_titles(q=""):
    selected = []
    for title in task_titles:
        if q.lower() in title.lower():
            selected.append(title)
    return selected

The local Study Tasks project instead preserves additions in JSON. After restarting, it reads that file to construct new Python records. Examine the existing add_task in the support.py listing; no new files are needed here.

The supplied read_records(path) loads the file’s JSON into Python records. write_records(path, records) saves the complete collection as JSON.

Read, Prepare, Save

The supplied prepare_task(title, category) builds a record with trimmed text and a generated identifier. The addition function appends that record to the list it just read, then saves the list:

def add_task(path, title, category):
    records = read_records(path)
    task = prepare_task(title, category)
    records.append(task)
    write_records(path, records)
    return task

The diagram below follows an addition into the JSON file and shows how a later run reads the saved collection.

Save a collection containing both the old records and the new record. Saving only the new record would lose earlier tasks.

Read the Current File on Each Operation

A GET route calls read_records(DATA_FILE) to display the current records. It does not call the writer. Starting the server also leaves the file’s contents unchanged.

Add a record through the browser and inspect tasks.json. Stop and restart the server, then refresh: the saved record should return.

The next exercise supplies a GET route that calls read_records(DATA_FILE) to display the current records. Complete the addition function so it saves a new task together with the existing records. This exercise is worth 40 points.

For the next trace, compare a Python record’s current title with the title saved in JSON.

records = [
    {"id": "T01", "title": "Make a plan", "category": "writing"}
]
write_records("tasks.json", records)
records[0]["title"] = "Review notes"

Next, apply these steps to a Reading Journal.

Check Your Understanding

1. Two tasks are added one after another. If the second addition saves a list containing only its new task, what happens to the first task, and why?
2. A search matches one task out of three. What could happen if the GET route saved that selected list back to tasks.json? Why should displaying the selection leave the file unchanged?
3. An addition is saved to new-tasks.json, while the GET route reads tasks.json. Why can saving succeed without the new task appearing, and which path values would you compare?