Do not use the DataAssist multiple insert record behavior to store cart information in the database.
included with eCart are 2 server behaviors for database manipulation:
eCart Store Order Summary
eCart Store Order details.
The Store Order Summary behavior is used to create one record in the orders table with information about who placed the order, what the billing address is, the shipping address and such.
the Store Order details behavior is used to store a record in the order details table for each line item in the cart.
you can set this up when using the Checkout Wizard, or you can do it manually by opening the server behaviors panel, click the plus button and going to ecart -> Database manipulation.
In either of those server behaviors, click the help button to go to the help documentation that explains how to use them.