I'm working on another Drupal site and as usual, it is going to make heavy use of the entityreference field to link entities together. Many of these fields are multiple value fields, and we need an easy way to allow editors to select multiple values from some long lists of potential values.
We have a couple options out of the box. We can display the options as checkboxes, an autocomplete field, or a drop-down select list. These are long lists, too long for checkboxes. And a long list in a multiple value select list is ugly and hard to use. That leaves the autocomplete, which is fine if you know what values to expect, but it's not very good for discovering or sorting through the available options. I'm looking for something that handles long multiple value lists better. It should make it easy to see what's been selected and what's available to be selected and be easy to use.
I finally pulled down a collection of possible Drupal 7 contributed modules to review to see what the options are. Here's a line up of some of the options with screen shots to show what each of them looks like and a little information about how to get them working and what they do.
For a point of reference, here's what the unvarnished Drupal multiple value selector looks like.
Multiple Selects
One option is Multiple Selects. This is a fairly simple rework that turns a single multiple value select list into a series of single value select lists, with an 'Add more' button. It's very easy to set up, just enable the module and choose the 'Multiple Selects List' widget as the widget.
Chosen
Another interesting option is Chosen. Chosen is based on a jQuery library that pulls together some of the benefits of both an autocomplete and a drop-down selector. The selected values are listed at the top of the selector. The bottom of the selector has a drop-down list of the available options. In between is an autocomplete box where you can type values that will be used to narrow the list.
To install this module, you have to enable the Libraries module and grab the jQuery Chosen library and drop it in sites/all/libraries/chosen. Then go to admin/config/user-interface/chosen and indicate when the Chosen selector should be applied. It can be set up to only apply to long lists of options and leave short lists alone and there is a jQuery selector that can be used to identify which elements it should be applied to. You need to set this up carefully because this will affect every select list on the site, not just those for a specific field.
Dynamic Multiselect
An additional possibility is the Dynamic Multiselect Widget. To use it you need to enable Dynamic Select and Entity Reference Dynamic Select Widget. Then you need to create a view using the 'Dynamic Select' display type. The view should be a list of the values you want to see in the select list. Finally, change the Entityreference field to use the Dynamic Select widget, and set up the widget to use the view that you just created.
The result looks like the following, where every selected item shows up with an individual selector. At the bottom is an 'Add more' button that you can use to select another option.
It took me a while to figure out what the 'Filter' options in the widget were for but I finally understood. Basically each drop down select list is a view, and the 'Filter' option to its right is a custom exposed filter for that view that allows you to filter the list to its left. I added a new filter to the view for the node title using the 'contains' operator, edited the field widget settings to indicate that I wanted to use the 'Title' filter in the widget, and after that I could type a title or partial title into the filter textfield and it would limit the list to its left to just the values that matched the value I typed in.
Entityreference Views Widget
Another option is Entityreference Views Widget. This widget uses a view to display the available options, making it possible to display lots more information about each option, like title, images, description, etc.
To install it, create a view of the items that should be displayed in the selector using a display of the type 'Entityreference Views Widget'. change the widget to the 'View' widget and select the view you just created. Then check the 'Display fields' tab for the content type being displayed in the widget and adjust the 'Entity Reference View Widget' view mode to identify the fields that you want to see in the selector.
This option makes it possible to see lots of information besides the title of the related items, so you could display images or descriptions to help indicate which is which. The downside of this widget is that it takes up a lot of space on the node form. It would be nice if it opened up in a modal window and just displayed just the selected items in the form to take up less space.
Improved Multi Select
The Improved Multi Select module is another option. To install it, enable the module, then go to admin/config/user-interface/improved_multi_select and choose the options. You can apply this to all multiple value selectors on the site, or indicate which ones to use, and you can indicate which paths to apply the effect on. At a minimum you will want to add 'select[multiple]' as the replacement. The result looks like the following:
jQuery UI Multiselect
Finally there is jQuery UI Multiselect. This is another jQuery effect. It requires the jQuery Update module. Once enabled multiple select form elements are transformed to look as follows:
The settings are controlled from admin/config/user-interface/jquery_ui_multiselect_widget. It will work out of the box with the default settings, but they can be adjusted.
Which is Best?
So that's my list. There are probably other alternatives but these are the ones I knew about or could find that have Drupal 7 releases. I don't want to even attempt to evaluate which of them is the 'best', because that depends on how you want to use it.
But I think it's helpful to see some of the available alternatives all in one place to help figure out which of them is the 'best' solution for your specific site.