External Lists using PowerForms
Since version 2.4, support for External Lists/External Content Types is available using PowerForms (SharePoint 2010 only).
Assuming you have already created your external list, to setup that list to use PowerForms, you should follow the steps below :
The PowerForms registration buttons should be available in the list ribbon, so register PowerForms for the New and Edit forms.
As you would normally do with any other form, open the designer and examine/change the default configuration created.
NOTE 1 : In some cases, the default control type may differ from the one you would expect. For example a database field of type "Tinyint" will create a NumberTextBox. If the purpose of the database field is to keep boolean values (1 or 0), just change the control type to CheckBox
NOTE 2 : The identifier of the record is no longer numeric, and is stored in a system field called BdcIdentity (a textbox control will be created for that column in case you want to use it)
Using Lookups bound to External Lists
Whenever you declare a lookup control based on an external list, SharePoint instead of binding the list to the lookup control, binds the external Data Source.
This has the result that the default form produced by PowerForms will not recognize the binding details and will leave the lookup control as a simple textbox.
What you have to do, is to change the control type to a ComboBox or a LookupPicker and set the properties manually through the control properties in the "Lookup Details" tab.
Type the list url, select the list name and in the value field, select the "BdcIdentity" field which is the actual record identifier.
Visit our blog for a more detailed example on External Lists and lookups on foreign keys.