Ricardo,
Whatever the language you choose, you'll meet 2 serious obstacles down
the road to a Web Application:
1. **Write responsive HTML/CSS/JS**: if you want to somehow clone the
layout of the forms of your VFP desktop application, and render it as
responsive HTML using - eg. - the Bootstrap framework, it'll take you up
to 10 levels of nested divs to get a proper layout; no GUI editor at the
rescue for that: you'll have to hard code using a text editor, and
choose appropriate class and IDs without getting messed up; and it soon
becomes very complex and difficult to handle, especially because CSS
computes the layout for you based on the structure and rules you define.
If you want a responsive layout, you can no longer set .left, .width,
etc., you must let the browser compute positions and dimensions.
Generating HTML is the area where your Python code will mostly be used
and, strangely, this is only the emerged part of the iceberg as point 2.
below explains.
2. **Maintain user state**: in your VFP code, each time you write
'thisForm…' or 'this…' or 'alias.field', or read a public variable, you
query (without knowing or realizing it) the user state, as it results
from the succession of user actions applied to some initial state. In
VFP, as a single instance of the application serves a single user,
everything can persist in memory: easy and painless. On the Web
conversely, as the same application can serve any user in any sequence,
the user state can exist only if you somehow maintain it (save and
restore). No framework, whether it's Python-based or C#-based, will ever
do that for you. Then you have roughly 2 options to maintain the user
state: **on the client or on the server**.
Maintaining the user state on the **client** requires to:
- write a lot of JavaScript, probably with some client-side framework
such as jQuery, Angular or Ember (be aware that these frameworks are
pretty conceptual and difficult to master properly; they at least
require that you are very proficient in HTML/CSS/JS as they add several
layers above these technologies). Whatever your choice, you write no
Python here, just HTML, CSS and JS.
- use client side storage to create on the client something similar to a
view that you'll submit to the server once user decides to save. This
requires a good knowledge of web storage API, another JavaScript-centric
technology
- expose all your business and presentation layer code to the outside
world; just like you would expose all the VFP code you have in *.scx and
*.vcx, except queries. You can only obfuscate this code (eg. minify
renames variables in alpha sequence such as "a", "b", "c", "d", etc.),
concealing it is impossible as the browser must read it.
This is the solution that most developers use nowadays; exchange with
the server are merely data conveyed in the JSON format.
Maintaining the user state on the **server** requires to:
- write double code: client side code altering the user interface is
almost the same, except it must query the user state from the server to
take proper action; the amount of code is much higher, and client and
server must somehow understand each other, this generally requires
either being a 'full stack developer' or defining tight rules (eg.
naming) between client and server.
- store user state on a server disk so that any web server can retrieve
the state for any user at any time (forget about assigning server
instances to specific users like in the desktop world, it just does not
work for high user counts; a typical web app serves 200 users and this
figure can go up to several thousands)
- choose or define a format to store user state: could be a simple JSON
string that the client JavaScript provides after each action (then you
need to choose a scalable structure), or a table that you can easily
query to, eg., find differences between states before / after user action.
FoxInCloud helps you dramatically in these 2 critical areas:
- **generate responsive HTML/CSS/JS code** from your VFP forms:
FoxInCloud understand how controls are aligned and grouped on the page
and builds the corresponding groupings (row, column, *-group) in the
Bootstrap CSS system
- **automatically maintains user state**: because FoxInCloud runs your
VFP forms on the server and these forms are object oriented, FoxInCloud
is able to detect what the user actions change on the form and save
these changes in a structured way; the same for the dataSession (views,
cursors, table states) and the general environment (public variables,
_Screen and _VFP custom properties, aliases in the default datasession).
FoxInCloud maintains the user state on server side, in tables using a
naming convention (user\form_[ante/post].dbf). The only thing you need
to do is: declare the native properties (eg. 'visible', 'enabled') that
the user action can affect (custom properties being saved by default);
FoxInCloud compares the state before and after user action to identify
the visual changes that the browser must apply: you have strictly
nothing to code to make this happen.
As I already often wrote, FoxInCloud can be regarded either as a final,
or just an intermediary step to a Web Application; you can:
- take advantage of the generated HTML/CSS/JS to save months of writing
responsive HTML
- judge whether the user state maintenance mechanism suits you and
eventually recode a similar mechanism in Python (or other)
- mitigate between a server-side and client-side user state maintenance
to save response time while protecting the code that you consider critical.
I would be delighted if VFP developers would consider FoxInCloud as a
community-inspired effort, and would like to cooperate towards a future
suitable migration path to the Web, rather than like a "take or leave"
product with the VFP stigmata.
FoxInCloud does incorporate thorough software engineering thinking about
running a Web Application while taking advantage of a Desktop
Application background, going far beyond and above the mere language
level which, in any case, does not and will never provide a complete
solution to building a Web Application.
Thierry Nivelet
FoxInCloud
Give your VFP app a second life in the cloud
http://foxincloud.com/
Le 12/03/2018 à 23:53, Ricardo Araoz a écrit :
Thanks Thierry, but I've gone over to Python, love the language and
libraries, gives me pleasure to write it. As for the 10x times, it
might be true if you are left to your own devices. But thankfully it
has loads of beautiful and useful libraries which allow me to keep
writing a language I've come to love.
Cheers
On 12/03/18 15:04, Thierry Nivelet wrote:
Ricardo,
Unless learning Python is for you so important and compelling that
you accept to spend 10x more time for the same result, did you look
at FoxInCloud?
Thierry Nivelet
http://foxincloud.com/
Give your VFP app a second life in the cloud
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