Object declarations in DataFlex can be nested allowing you to declare one object inside another. The outer object is referred to as the parent and the inner objects are its children. The parent object is said to contain its children.
Object nesting is analogous to models of things that we see in the real-world. For example the structure of a car. A car can be thought of as a compound object that is constructed from smaller component objects, such as 4-wheels, a chassis, engine, body and so on. Each of these smaller components is also made up from other objects; an engine contains pistons, a crank, valves, etc.
A real-world example of a compound object
In terms of a computer application, let's imagine an order entry application. A typical Order Entry application is composed of many distinct modules; a customer maintenance view, an order entry view; a print orders view; an inventory maintenance view and so on. Each one of these views contains multiple identifiable entities. A customer maintenance view, for example, will contain buttons, edit forms, labels, tabbed forms, combos, etc.
A customer entry view demonstrating nested entities
DataFlex represents this structure by nesting objects of different types inside each other. The structure of objects that you create in an application will be determined by its design specification. Below is the DataFlex object structure that was used to define the customer entry view shown above.
Object Customer is a dbView
Set Label to "Customer Entry View"
Set Size to 162 283
Object Customer_DD is a Customer_DataDictionary
End_Object
Set Main_DD to Customer_DD
Set Server to Customer_DD
Object Customer_Number is a dbForm
Entry_Item Customer.Customer_number
Set Label to "Customer Number:"
Set Size to 13 42
Set Location to 5 72
End_Object
Object Customer_Name is a dbForm
Entry_Item Customer.Name
Set Label to "Name:"
Set Size to 13 186
Set Location to 20 72
End_Object
Object CustTD is a dbTabDialog
Set Size to 105 265
Set Location to 36 7
Object Address_TP is a dbTabPage
Set Label to "Address"
Object Customer_Address is a dbForm
Entry_Item Customer.Address
Set Label to "Street Address:"
Set Size to 13 180
Set Location to 8 62
End_Object
Object Customer_City is a dbForm
Entry_Item Customer.City
Set Label to "City/State/Zip:"
Set Size to 13 84
Set Location to 24 62
End_Object
Object Customer_State is a dbComboForm
Entry_Item Customer.State
Set Size to 13 32
Set Location to 24 152
End_Object
// etc.
End_Object
Object Balances_TP is a dbTabPage
Set Label to "Balances"
Object Customer_Credit_Limit is a dbForm
Entry_Item Customer.Credit_limit
Set Label to "Credit Limit:"
Set Size to 13 48
Set Location to 9 72
End_Object
// etc.
End_Object
Object Comments_TP is a dbTabPage
Set Label to "Comments"
Object Customer_Comments is a dbEdit
Entry_Item Customer.Comments
Set Size to 60 242
Set Location to 15 9
End_Object
End_Object
End_Object
End_Object
Note that this example uses the Entry_Item command. Refer to the DataFlex Language Reference for more information on this command.