Managing Database File Records and ADG Dataset

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The .NET Framework provides the ( DataSet ) class as a general-purpose container for relational database data. DataSet objects offer many useful functions and are used throughout the framework and in data-centric components for access, update, and display. For example, DataSet objects can be bound to certain Windows forms controls at design-time. DG builds on this foundation by sub-classing DataSet in its own AdgDataSet class. AdgDataSet effectively provides a bridge between the record-oriented access world of DataGate and AVR and set-oriented access methods. For a complete introduction to DataSet , please consult the .NET Framework documentation.

AdgDataSet objects consist of one or more ( DataTable ) objects. These DataTables represent each format of the file. The DataTables contain a collection of ( DataRow ) objects. In DG, database file records are contained by DataRow objects. Field data of records are accessed by field name or through ( DataColumn ) objects, which reference the data and metadata of “columns” in DataRow objects. AdgDataSet adds methods and properties, such as ActiveRow and PrepareRow, to facilitate quick, familiar access patterns to the data in AdgDataSets .

AdgDataSet introduces the notion of an “active row” in a DataSet . This is the row which represents the database record to be accessed. For example, when a database record is read by one of FileAdapter’s read methods, the AdgDataSet’s ActiveRow property is set to reference the DataRow object added to AdgDataSet to contain the database record read.

Although DG uses the facilities of a DataSet to represent record formats as a set of DataTables , AdgDatSet provides several methods which automate access to those tables with familiar record format specifications. DeleteRow, AddRow, InsertRow, and PrepareRow all provide direct access to DataRow objects in DataTables corresponding to a specific record format.

As records are read from a file or added via InsertRow they accumulate in the DataTable for the format. The ActiveRow property only references the last record read - previously read/inserted records remain in the DataTable until they are explicitly removed, via DataSet.Clear or DataTable.Clear. To access or specify accumulated DataRow objects, the DeleteRow , InsertRow , and SetActive methods provide a RRN parameter.

Note that accessing DataRow objects in AdgDataSet is not the same as accessing records in a database file. Database records can only be read, added, updated, and removed via FileAdapter methods. AdgDataSet methods only access the in-memory representation of a database file’s formats, not the underlying database file. FileAdapter methods use the AdgDataSet as a repository for database records read, added, and updated.

Managing Database File Records and ADG Dataset

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