Flask采暖系统配置器POST请求无法跳转至/cart路由及TypeError问题求助

Hey there, let's break down what's going wrong here and fix it step by step—you're so close to wrapping this up!

The Core Issue: Broken Form Submission #

The biggest problem is a tiny syntax error in your search.html template that's causing the "Choose" button to submit to the wrong route. Look at your form tag:

<form action "/cart" method="post">

You're missing an equals sign (=) after action. Browsers can't parse this correctly, so they default to submitting the form to the current page—the /search route—instead of /cart. That's why you're hitting the TypeError when you click "Choose": the /search route tries to read the output parameter, which doesn't exist in this form submission.

Step 1: Fix the Form Tag #

Update the form in search.html to use the correct syntax:

<form action="/cart" method="post">
<input name="bom_id" type="hidden" value="{{ cascades["id"] }}">
<input class="btn btn-primary" type="submit" value="Choose">
</form>

This will make the form submit directly to /cart when clicked, which is exactly what you want.

Step 2: Add Guard Rails to the /search Route #

Even after fixing the form, it's smart to add checks to prevent the NoneType error from happening in other scenarios (like someone manually visiting /search without submitting the form). Update your search function:

@app.route("/search", methods=["GET", "POST"])
def search():
    # Only process POST requests (from the initial form submission)
    if request.method != "POST":
        return redirect(url_for("index"))
    
    output = request.form.get("output")
    # Validate output exists and is a number
    if not output or not output.strip().isdigit():
        return render_template("index.html", error="Please enter a valid numeric output value")
    
    hydraulic = request.form.get("hydraulic")
    layout = request.form.get("layout")
    # Validate required dropdowns are selected
    if not hydraulic or not layout:
        return render_template("index.html", error="Please select hydraulic and layout options")
    
    try:
        min_output = int(output) - 15
        max_output = int(output) + 15
    except ValueError:
        return render_template("index.html", error="Please enter a valid number for output")
    
    cascades = db.execute(
        "SELECT * FROM cascades WHERE hydraulic = ? AND layout = ? AND output BETWEEN ? and ?",
        hydraulic, layout, min_output, max_output
    )
    return render_template("search.html", cascades=cascades)

These checks ensure that only valid submissions make it through to the database query, and give users clear feedback if they miss a field.

Step 3: Hardening the /cart Route #

To fix the "no data displayed" issue you saw earlier, add validation to the cart route to ensure the bom_id is passed correctly and handle cases where no BOM is found:

@app.route("/cart", methods=["GET", "POST"])
def cart():
    # Only process POST requests (from the "Choose" button)
    if request.method != "POST":
        return redirect(url_for("index"))
    
    bom_id = request.form.get("bom_id")
    if not bom_id:
        return render_template("index.html", error="Invalid system pack selection")
    
    bom = db.execute("SELECT * FROM bom WHERE bom_id = ?", bom_id)
    # Handle cases where no BOM matches the ID
    if not bom:
        return render_template("bom.html", bom=[], error="No BOM found for this system pack")
    
    return render_template("bom.html", bom=bom)

You'll also want to update bom.html to display the error message if it exists:

{% extends "layout.html" %}
{% block body %}
{% if error %}
<div class="alert alert-danger">{{ error }}</div>
{% endif %}
<h3>System Pack BOM</h3>
<!-- Your BOM table/listing here -->
{% endblock %}

Testing the Fix #

1. Restart your Flask app
2. Submit the initial form with a valid output value (like 200)
3. Click "Choose" on any system pack option—you should now be redirected to /cart and see the corresponding BOM

With these changes, your app should behave exactly as you intended: showing system pack options, then loading the correct BOM when a user selects one.

内容的提问来源于stack exchange，提问作者Michael Berry