The External Content Type Adapter allows mashups to support the following SharePoint list operations required for external content lists:
Read List: to return all items for the list. This case simply returns the entire results of the mashup.
Read List Item: to return a single list time by ID. This case requires an input parameter to specify the ID of the specific row in mashup results to return.
Mashups have only one operation to run the mashup and return all results. To support these two separate operations for SharePoint lists from one mashup, the External Content Type Adapter block requires an mashup input parameter for an item ID.
An item ID of 0 matches the case where all list items must be returned to SharePoint.
Any other item ID matches the case where a specific list item should be returned.
In most cases, the other operations available for external content lists in SharePoint to create, update or delete list items cannot be supported by ECT-enabled mashups because the underlying information sources (mashables or mashups) used by ECT-enabled mashups do not support these operations.