Initializes a System.Data.IDbCommand object to get the 'External Store' GUID that corresponds to the sopInstanceUid in the 'External Store'.
command
Type: System.Data.IDbCommand The database command that will be initialized to execute the query.
sopInstanceUid
The SOP Instance UID that identifies the instance.
Data can be stored on more than one 'External Store'. For each 'External Store', there is a corresponding add-in. Each add-in can be identified by a global unique identifier.