Creating External Lists: Tips and Warnings
Applies to: SharePoint Server 2010
The following are important points to know about working with external lists.
External lists only support fields that have flat structure. If you want to show complex fields, then you need to either use complex formatting (See How to: Use Complex Formatting in the Model to Show Complex Fields) or create custom field types in Microsoft SharePoint Server to display the complex field (See How to: Create Custom Field Types in SharePoint).
If you use an external list that contains a complex field, using complex formatting will flatten the complex type, thus disabling write-back to the external data source.
The external content type model definition must include a SpecificFinder definition and at least one Finder definition. Finder view must be the same or a subset of the SpecificFinder view. Microsoft Business Connectivity Services (BCS) will create as many views for the external list as there are Finders defined for that Entity. At run time, users can choose the view they want by using the SharePoint Ribbon.
Passthrough authentication will not work if there is a double-hop issue, that is, if the back-end database and SharePoint Server are on different servers. You should use RevertToSelf or Secure Store Service instead.
If you are using RevertToSelf for authenticating to the external system, make sure that the network account you use has permissions on the back end.
Money fields in external lists are not displayed in the format money fields are displayed in a custom list. One way to work around this is to write a custom field type for the currency and use it in the BDC model accordingly for the money fields. Another way is to specify your own XSLT transformation of the external list Web part.