Two registration forms: simple + long-form?

Is it possible to create a second, shorter site registration form to be used at events with very few fields (i.e., name, email address, mobile number) to complement the existing, longer registration form with more required fields?

Completing the shorter registration form at an event would send an email message to the new member with a link requesting completion of the longer form.

Found a couple of extensions, which may help, but not sure if they would provide exactly this functionality, since only one profile type is desired, and the longer form should be standard for those who register on the web (not an event):

Profile Types Splitter Basic
Single Line Join Form

As an alternative, would a simple web form with a few fields on it that updates the database when submitted do the trick?

Thanks in advance!

you can make your registration form as short or as long as you want it to be - and the user can fill in any other fields in the profile edit page. As in my case - the registration form is just username, email and password - then once logged in - on the account page - it has a message saying that the user has only completed x% of their profile with a link to the profile edit page.

I would suggest to use a custom-coded simple join form for short variant. I don't think the Profile Types Splitter will suit well for this particular task although it is still possible to achieve the goal with a few tricks in it. 

Do you mean a completely custom-coded simple join form or a customized version of this extension?

Single Line Join Form

A completely custom-coded simple join form. 

What about using Profile Types Splitter Basic extension to create the short registration form, then using its migration tool to merge registrations created with the short form into the single profile type used on the site?

Maybe Single Line Join Form extension can then be used to remind new registrations using the short form to complete their profiles when they log in using its profile completion notification popup feature.

What do you think of this approach?

In this case you will have to deal with ProfileTypes, i.e. a user must choose a form/profile type himself during registration. May be a Conditional Fields can fit better for your particular case, but in this case a member would still have to select his type of form himself. Also actually I don't see any sense in using the migration tool. It was designed to assign a certain profile type to all members of a certain membership level.

Unfortunately no, the Single Line Join form just adds a single-line join form, it not affects the profile edit form in anyway, neither it provides a notifications/reminders to existing profiles.

P.S. Reading your original goal description at the very top I'd still recommend to go with a custom-coded simple HTML form + additional email notifications for this particular form. Optionally you can install some module that will remind the registered members that their profile is not completed. 

Thanks for your response!

Custom-coded HTML form which would simply insert values into the database and not necessarily follow the Dolphin object model?

A custom-coded PHP form which will follow the Dolphin object model and will simply interact with it to create a profile. Because the form must have all the server-side data validation that is already built-in into Dolphin's framework, in addition there are many other things happening during profile creation besides the DB insert record. And also because it is still necessary to alter the join process and force Dolphin to not require all the other fields to be provided when this particular join form is used.

Again, thanks for your response.

Is there documentation describing this object model which would help me develop something like this?

Have developed MVC in PHP using frameworks, but looking at Dolphin code, I honestly can't figure out what's going on. It contains unique constructs and implementations which aren't readily apparent without substantial effort.

Thanks!

As far as I know - no, there is no any documentation available for this. Dolphin is a proprietary framework itself (+ a lot of legacy non object-oriented code). 

If you'd like to develop that join form yourself then I'd suggest to take a look at 

inc/classes/BxDolJoinPage.php

inc/classes/BxDolProfileFields.php

inc/classes/BxDolProfilesController.php

Great, thanks!

Here's a question:

How do you make customizations, like adding a join form in this case, and ensure they're not lost when Dolphin is updated?

 It depends. The main rule is pretty obvious - do not alter anything in Dolphin's core files. There are a number of ways to do that, like using custom pages, using Dolphin's alerts and injections systems, overriding behavior in a subclasses, or if none of the above is possible then simply documment the change and reapply it if necessaary after an update. 

Are there any examples or reference documentation available on how to do this?

Thanks!

 You can try to find something useful here.

Is it true that during Dolphin updates, while changes to code files are susceptible to being lost, database changes are preserved?

It is true.