FireDAC.TFDQuery.MasterDetail Sample

This sample demonstrates how to use the TFDQuery component in order to set up master-detail relationships between datasets.

Location

You can find the MasterDetail sample project at:

• Start | Programs | Embarcadero RAD Studio Athens | Samples and then navigate to:
  • Object Pascal\Database\FireDAC\Samples\Comp Layer\TFDQuery\MasterDetail
• Subversion Repository:
  • You can find Delphi code samples in GitHub Repositories. Search by name into the samples repositories according to your RAD Studio version.

Description

The MasterDetail sample shows you how to set up master-detail relationships between datasets using two TFDQuery objects. The sample uses the master-detail relationship to automatically filter a detail dataset based on a current master dataset record. In this sample, the master dataset has "Order" records, and the detail dataset shows only lines for the current order. Moreover, you can modify in run time the Cache property of TFDFetchOptions to control the data allocation in cache memory.

How to Use the Sample

1. Navigate to the location given above and open Qry_MasterDetail.dproj.
2. Press F9 or choose Run > Run.

Files

File in Delphi	Contains
Qry_MasterDetail.dproj Qry_MasterDetail.dpr	The project itself.
fQueryMasterDetail.pas fQueryMasterDetail.fmx	The main form.

Implementation

To set up a master-detail relationship, this sample uses the Object Inspector to configure the following components at design time as follows:

• Two TFDQuery objects named qryOrders and qryOrderDetails. These components are used to implement a dataset capable of executing SQL queries. The following setup is needed:

• Configure the Connection property of both components to specify the FireDAC connection object that is used to connect to a DBMS.

In order to set up a master-detail relationship, the SQL properties of both components have to be set up using the Object Inspector at design time as follows:

• The SQL property of qryOrders is set to select * from {id Orders} in order to select "Order" records.
• The SQL property of qryOrderDetails is set to select * from {id Order Details} where OrderID = :OrderID in order to select "Order Details" records.

Finally, both objects are linked in a master-detail relationship, where qryOrders is the master dataset and qryOrderDetails is the detail dataset. To this end, you have to set up the following properties of qryOrderDetails:

• MasterFields is set to ORDERID.
• IndexFieldNames is set to ORDERID.
• MasterSource is set to dsOrders.

• Two TDataSource objects named dsOrders and dsOrdDetails. These components provide an interface between a dataset component and data-aware controls on a form. In this sample, it is used to provide communication between the datasets and the grids where the datasets are displayed. To this end, the following properties are set up at design time using the Object Inspector:

• The DataSet property of dsOrders is set to qryOrders and the DataSource property of DBGrid2 is set to dsOrder.
• The DataSet property of dsOrderDetails is set to qryOrderDetails and the DataSource property of DBGrid1 is set to dsOrderDetails.

When you run the application, click on the Use Connection Definition combo box and select an option in order to define a connection. When you select an item of the combo box, the sample uses the Open method of qryOrders and qryOrderDetails in order to execute the SQL statements that retrieves the corresponding datasets from the database. Then, the sample displays the master and the detail datasets using a two TDBGrid components. The DBGrid2 is used to display and manipulate records from the master dataset, while the DBGrid1 is used to display and manipulate records from the detail dataset. Once the grids are filled, you can interact with the Cache details check box and the Refresh master and Refresh details buttons. These components have events attached to them to do the following:

• The Cache details check box includes fiDetails into the FetchOptions.Cache property of qryOrderDetails if the check box is checked. It means that if it is checked, the associated detail record will not be discarded from the memory after changing a master dataset record.
• The Refresh master button uses the Refresh method to re-fetch the master data from the database.
• The Refresh details button uses the Refresh method to re-fetch the detail data from the database.

Uses

• TFDQuery
  • FetchOptions.Cache
  • Refresh
• TFDConnection
• TDataSource

See Also

• FireDAC
• Defining Connection (FireDAC)
• Master-Detail Relationship (M/D)
• Fetching Rows (FireDAC)

Samples

• FireDAC Connection Definition sample
• FireDAC TFDMemTable Master-Detail Relationship sample