fastapi doc : from post doc

Docs/Services/FastAPI/12-From-Post.md

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+# FastAPI – POST Requests with Form Data
+
+This document demonstrates how to handle **form-based POST requests** in FastAPI using the `Form()` dependency.
+Form data is commonly used in **HTML forms**, authentication flows, and legacy systems.
+
+---
+
+## Example Application
+
+Create or update `main.py` with the following content:
+
+```python
+from fastapi import FastAPI, Form, status
+from fastapi.responses import JSONResponse
+
+app = FastAPI()
+
+users_db = [
+    {"id": "1", "name": "radin", "password": "123"}
+]
+
+
+@app.post("/user/")
+def get_user_from_form(
+    target: int = Form(
+        ...,
+        gt=0,
+        alias="User ID",
+        description="Enter target unique ID",
+    )
+):
+    for item in users_db:
+        if item["id"] == str(target):
+            return JSONResponse(
+                content={"msg": f"Your target user name is {item['name']}"},
+                status_code=status.HTTP_200_OK,
+            )
+
+    return JSONResponse(
+        content={"msg": "user not found"},
+        status_code=status.HTTP_404_NOT_FOUND,
+    )
+```
+
+---
+
+## Form Data Overview
+
+### What is Form Data
+
+Form data is sent in the request body using:
+
+```
+Content-Type: application/x-www-form-urlencoded
+```
+
+or
+
+```
+multipart/form-data
+```
+
+FastAPI requires the `Form()` dependency to explicitly declare form inputs.
+
+---
+
+## Endpoint Behavior
+
+### Endpoint
+
+```http
+POST /user/
+```
+
+### Request Body (Form Data)
+
+```
+User ID=1
+```
+
+### Example Using `curl`
+
+```bash
+curl -X POST "http://localhost:8000/user/" \
+  -H "Content-Type: application/x-www-form-urlencoded" \
+  -d "User ID=1"
+```
+
+---
+
+## Response Examples
+
+### Success Response
+
+```json
+{
+  "msg": "Your target user name is radin"
+}
+```
+
+Status Code: **200 OK**
+
+---
+
+### Failure Response
+
+```json
+{
+  "msg": "user not found"
+}
+```
+
+Status Code: **404 Not Found**
+
+---
+
+## `Form()` Parameter Configuration
+
+```python
+Form(
+    ...,
+    gt=0,
+    alias="User ID",
+    description="Enter target unique ID"
+)
+```
+
+| Parameter     | Description                     |
+| ------------- | ------------------------------- |
+| `...`         | Field is required               |
+| `gt=0`        | Value must be greater than zero |
+| `alias`       | Custom form field name          |
+| `description` | Displayed in API docs           |
+
+---
+
+## Swagger / OpenAPI Behavior
+
+* Form fields appear as input fields
+* Aliases are reflected in the UI
+* Validation rules are enforced automatically
+* Errors are returned with clear messages
+
+---
+
+## Running the Application
+
+Start the service using `uvicorn`:
+
+```bash
+uvicorn main:app --reload
+```
+
+---
+
+## Best Practices
+
+* Use form data only when required (e.g. HTML forms)
+* Prefer JSON for APIs and services
+* Avoid exposing sensitive fields in plain form data
+* Use HTTPS for all form submissions
+* Validate and sanitize all inputs
+* Use authentication and hashing for passwords
+* Do not store credentials in plain text
+