Delphi Programming Guide
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Part I - Foundations
  Chapter 1 Delphi 7 and Its IDE
  Chapter 2 The Delphi Programming Language
  Chapter 3 The Run-Time Library
  Chapter 4 Core Library classes
  Chapter 5 Visual Controls
  Chapter 6 Building the User Interface
  Chapter 7 Working with Forms
Part II - Delphi Object-Oriented Architectures
  Chapter 8 The Architecture of Delphi Applications
  Chapter 9 Writing Delphi Components
  Chapter 10 Libraries and Packages
  Chapter 11 Modeling and OOP Programming (with ModelMaker)
  Chapter 12 From COM to COM+
Part III - Delphi Database-Oriented Architectures
  Chapter 13 Delphi's Database Architecture
  Chapter 14 Client/Server with dbExpress
  Chapter 15 Working with ADO
  Chapter 16 Multitier DataSnap Applications
  Chapter 17 Writing Database Components
  Chapter 18 Reporting with Rave
Part IV - Delphi, the Internet, and a .NET Preview
  Chapter 19 Internet Programming: Sockets and Indy
  Chapter 20 Web Programming with WebBroker and WebSnap
  Chapter 21 Web Programming with IntraWeb
  Chapter 22 Using XML Technologies
  Chapter 23 Web Services and SOAP
  Chapter 24 The Microsoft .NET Architecture from the Delphi Perspective
  Chapter 25 Delphi for .NET Preview: The Language and the RTL
       
  Appendix A Extra Delphi Tools by the Author
  Appendix B Extra Delphi Tools from Other Sources
  Appendix C Free Companion Books on Delphi
       
  Index    
  List of Figures    
  List of tables    
  List of Listings    
  List of Sidebars  

 
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Master/Detail Structures

Often, you need to relate tables that have a one-to-many relationship. This means that for a single record in the master table, there are many detailed records in a secondary table. A classic example is an invoice and the items of the invoice; another is a list of customers and the orders each customer has placed.

These are common situations in database programming, and Delphi provides explicit support with the master/detail structure. The TDataSet class has a DataSource property for setting up a master data source. This property is used in a detail dataset to hook to the current record of the master dataset, in combination with the MasterFields property.

Master/Detail with ClientDataSets

The MastDet example uses the customer and orders sample datasets. I added a data source component for each dataset, and for the secondary dataset I assigned the DataSource property to the data source connected to the first dataset. Finally, I related the secondary table to a field of the main table, using the MasterFields property's special editor. I did all this using a data module, as discussed in the earlier sidebar "A Data Module for Data-Access Components."

The following is the complete listing (but without the irrelevant positional properties) of the data module used by the MastDet program:

object DataModule1: TDataModule1
  OnCreate = DataModule1Create
  object dsCust: TDataSource
    DataSet = cdsCustomers
  end
  object dsOrd: TDataSource
    DataSet = cdsOrders
  end
  object cdsOrders: TClientDataSet
    FileName = 'orders.cds'
    IndexFieldNames = 'CustNo'
    MasterFields = 'CustNo'
    MasterSource = dsCust
  end
  object cdsCustomers: TClientDataSet
    FileName = 'customer.cds'
  end
end

In Figure 13.18, you can see an example of the MastDet program's main form at run time. I placed data-aware controls related to the master table in the upper portion of the form, and I placed a grid connected with the detail table in the lower portion. This way, for every master record, you immediately see the list of connected detail records—in this case, all orders placed by the current client. Each time you select a new customer, the grid below the master record displays only the orders pertaining to that customer.

Click To expand
Figure 13.18:  The MastDet example at run time

 
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