How to change form values sent by a module?

Question

I've just coded a module in J!3.7 which should auto-generate the values of optional fields based on another required field value on save. I know that I can check values using a rule class but I had no luck overwriting the form fields there so I think it's just not possible this way. Unfortunately, I haven't found any documentation about this. I'm using a subform so things also get a bit more complicated. In my test()-function

$input->get( 'params.gmcp_content.gmcp_content0.gmcp_lng' ); // returns 8.4368239

returns the expected value which was entered manually and saved properly before to have test case. So I tried this to set the value:

$input->set( 'params.gmcp_content.' . $key . '.gmcp_lng', $lng );

But this didn't work. Neither did this:

$form->setValue( 'params.gmcp_content.' . $key . '.gmcp_lng', null, $lng );

When I dump the post array, it looks like this:

Array
(
    [jform] => Array
        (
            [title] => Locations
            [params] => Array
                (
                    [gmcp_content] => Array
                        (
                            [gmcp_content0] => Array
                                (
                                    [gmcp_contact_id] => 2
                                    [gmcp_lat] => 49.3161506 // entered manually for testing
                                    [gmcp_lng] => 8.4368239 // entered manually for testing
                                )
                            [gmcp_content1] => Array
                                (
                                    [gmcp_contact_id] => 1
                                    [gmcp_lat] => 
                                    [gmcp_lng] => 
                                )
                        )
...
)

So how can I manipulate form data before the module params get saved in the database?

Answer 1

If you're talking about module definition file that holds module options you can't do much in the file using framework it-self. But you can do it in 3 other ways.

In the UI by Java Script

Just create custom field class that will include Java Script into document head that will perform a sample data fill on save/apply button click. Here is some short tutorial about creating custom Joomla! form field. It requires from you both PHP, Joomla Framework and Java Script knowledge but it gives you most possibilities. If its only about changing settings depending on other input values in form. Its the best option.

In module helper

If you don't need the data to alter system behaviour (for example by selecting a layout, bootstrap size or caching) you can alter the data when it is retrieved in your module helper (or directly in your module main file). You should use that one if you need to change data pushed to the module depending on values from the database or other extensions. That way the module settings holds only the params, and processing is made by the module it-self.

As a separate plugin

As @Rico pointed out there is also a possibility to use a plugin from extension group and onExtensionBeforeSave event. If you gonna need to install both module and plugin at once use Package extension type. Details about creating package can be found here. This is the last resort. It makes the job done but also creates a problem if a data sources changes. Then you would have to update the module too (at least open and save).

Answer 2

Well, after a long series of struggles I've found at least one way which finally worked for my situation. I had to code a plugin, a fact which feels very counter-intuitive and oversized to me ... what I don't like about this solution is that it's not "bundled" with the module what it should be. Anyways here's my solution:

// IMPORTANT:
// in your "myplugin.xml": "group" must be "extension":
// <extension version="3.1" type="plugin" group="extension" method="upgrade">
// in your "myplugin.php": class name must start with "PlgExtension"

class PlgExtensionMyPlugin extends JPlugin {

    public function onExtensionBeforeSave( $context, &$table, $isNew ) {

        // not the right context
        if( $context !== 'com_modules.module' ) {
            return true;
        }
        // not the right module
        if( $table->module !== 'mod_mymodule' ) {
            return true;
        }

        // get the params of the module
        $params = json_decode( $table->params );


        // ... process $params in some way


        // build params json string and assign new params value to module reference
        $table->params = json_encode( $params );

        return true;
    }
}

Don't forget to ACTIVATE your plugin after installing it.