Error handling in Business Components

Upon executing the Save, Check, Load or Delete methods, the messages automatically generated by GeneXus (those issued by GeneXus through data consistency controls, uniqueness of Primary Key values, etc.) are triggered as well as your own Error and Msg rules defined in the Transaction object.

Even when these controls are automatically triggered, for the end user to be aware of this, you must obtain and explicitly show the messages issued.

Now, how do you recover the messages occurred?

You use the structured data type Messages that GeneXus defines automatically upon creating a New - Knowledge Base: 

 

This collection data type is meant to allow access to the messages issued in the execution of a Business Component.

So, with the object to use the Business Component you define two variables:

• &Messages: of the Messages data type, collection
• &oneMessage: of the Messages.Message data type, which is 1 element in the collection

Example

Suppose you define the Customer Transaction as Business Component (by setting its Business Component property = True):

Customer                                                                  
{                                                                           
  CustomerId*     (Autonumber property = True)                             
  CustomerName                                                              
  CustomerAddress                                                      
  CustomerPhone
  CustomerEmail
  CustomerBirthDate
  CustomerAddedDate
  CountryId
  CountryName   
}

Country Transaction:

Country
{
  CountryId*     (Autonumber property = True)
  CountryName
}

Customer rules:

Default(CustomerAddedDate,&today);
error('The customer must be 18 years old or more') if CustomerBirthDate.Age()<18;

Accordingly, a Business Component data type of the Customer Transaction is automatically created in the Knowledge Base and you can define in any object a variable of the new type created. Thus, in any object you define a variable named &customer based on the Customer type and:

1.  - you codify what you need to do with the &customer variable
2. - you apply the Save method to the &customer variable
3. - you want to handle the errors that may have occurred, so, the following code shows how you can obtain the errors that happened in a collection variable and iterate the collection for advising the user (or doing something else):

 &customer.save()
If &customer.Fail()
   &Messages = &customer.GetMessages()             //you obtain the messages that may have ocurred (you extract and load them in the &Messages collection)
   for &oneMessage in &Messages                    //you iterate the collection
      Do case
      Case &oneMessage.Id ='PrimaryKeyNotFound'   
           msg('The customer does not exist')
      Case &oneMessage.Id ='ForeignKeyNotFound' 
           msg('The country does not exist') 
      Case &oneMessage.Id= 'RecordWasChanged' 
           msg('The customer record was changed by another user')         
      Case &oneMessage.Id ='DuplicatePrimaryKey'   
           msg('A customer with equal identifier already exists')
      Otherwise
           msg(&oneMessage.Description) 
      Endcase       
   endfor
endif

   -   "Id", however they can be just a code like "1", "2", "3" or "Error1", "Error2", recommended to define explanatory texts id like "CustomerNameCannotBeEmpty". The reason is that the code will be clearer. For example: "If &Customer.GetMessages().Item(1).Id=CustomerNameCannotBeEmpty is clearer than "If &Customer.GetMessages().Item(1).Id=1"

Type

The "Type" is based on a enumerated domain. You can ask about this values: MessageTypes.Warning and MessageTypes.Error.