Add records access control example

[VitaliyMF]

Sometimes access to the database records should be controlled on a data layer. Typical situations:

• SaaS applications that use single database for all "instances"; in this case data is isolated by adding something like "instance_id" or "client_id' in all tables. Data layer should guarantee that business logic will able to select/update/delete records only of the current "instance".

• business apps where access to the records is controlled by some rules. For instance, someone should able to select a record only if it is "assigned" to this record.

NReco.Data supports this kind of access control; it is possible to add extra 'access control' conditons to the Query before execution by wrapping IDbCommandBuilder (responsible for ADO.NET commands generation by Query). Lets add simple example to illustrate this approach.