Clean create_host view

Use the session instead of URL parameters to store the last network
chosen.

app/main/views.py

@@ -10,7 +10,7 @@ This module implements the main blueprint.
 
 """
 import sqlalchemy as sa
-from flask import (Blueprint, render_template, jsonify,
+from flask import (Blueprint, render_template, jsonify, session,
                    redirect, url_for, request, flash, current_app)
 from flask_login import login_required
 from .forms import AttributeForm, HostForm, ItemForm
@@ -156,17 +156,17 @@ def list_hosts():
 @bp.route('/hosts/create', methods=('GET', 'POST'))
 @login_groups_accepted('admin', 'create')
 def create_host():
-    # Try to get the network_id from the URL parameters
-    # to display the form with the same selected network
-    # when reloading the page (redirect after submit)
+    # Try to get the network_id from the session
+    # to pre-fill the form with the same network
     try:
-        network_id = request.args['network_id']
+        network_id = session['network_id']
     except KeyError:
         # No need to pass request.form when no extra keywords are given
         form = HostForm()
     else:
         form = HostForm(request.form, network_id=network_id)
     if form.validate_on_submit():
+        network_id = form.network_id.data
         host = models.Host(ip=form.ip.data,
                            network_id=form.network_id.data,
                            name=form.name.data,
@@ -182,7 +182,9 @@ def create_host():
             flash(f'{e}', 'error')
         else:
             flash(f'Host {host} created!', 'success')
-        return redirect(url_for('main.create_host', network_id=host.network_id))
+        # Save network_id to the session to retrieve it after the redirect
+        session['network_id'] = host.network_id
+        return redirect(url_for('main.create_host'))
     return render_template('create_host.html', form=form)