meeting the challenges of uninformative messages when deleting object

This article addresses the question cancel values from a table storing the master used in other objects.

The question of how to remove the values considered in the paper Cascade deleting objects.

Attempt removal wizard

Given the following diagram:

If in the database there are objects of type Клиент referencing it when trying to delete object of type Адрес error is displayed:

The database will not delete such an object, and the user will be uninformative message.

solution to the problem

To solve this problem is to use the business server of a deleted object:

  • To know the number of objects that reference the deleted.
  • If it is not equal to 0, throw exception with a user-friendly description of the problem.
  • If necessary, catch the exception and handle in a special way.

Example

For the above-described conditions: to add validation to a business class server Адрес:

if (UpdatedObject.GetStatus() == ObjectStatus.Deleted)
{
    // Find the number of clients that reference the deleted address. 
    var ds = (MSSQLDataService)DataServiceProvider.DataService;
    var clientsCount = ds.Query<Клиент>(Клиент.Views.КлиентE).Where(k => k.Прописка.__PrimaryKey == UpdatedObject.__PrimaryKey).Count();

    // If the customer is not 0, throw an exception. 
    if (clientsCount != 0)
    {
        throw new Exception(string.Format("Could not remove Address. At this address is home to {0} client(s)(s)", clientsCount));
    }
}

As a result, when you try to remove the address at which the registered clients, the user will give the following message:

The message has changed to be more meaningful.

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