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.

Figure 13.18:  The MastDet example at run time