Data Shaping Overview
Data shaping means building hierarchical relationships between two or more logical entities in a query. The hierarchy can be seen in parent-child relationships between a record of one Recordset, and one or more records (also known as a chapter) of another Recordset. In a parent-child relationship, the parent Recordset contains the child Recordset. An example of such a hierarchical relationship is customers and orders. For every customer in a database, there can be zero or more orders. The hierarchical relationship can be recursive, meaning that grandchild records can be nested in a child record. In principle, a hierarchical record can be nested to any depth. In practice, ADO limits the recursion to a maximum of 512 Recordsets.
In general, columns of a shaped Recordset can contain data from a data provider such as Microsoft® SQL Server, references to another Recordset, values derived from a calculation on a single row of a Recordset, or values derived from an operation over a column of an entire Recordset. A column can also be newly fabricated and empty.
When you retrieve the value of a column that contains a reference to another Recordset, ADO automatically returns the actual Recordset represented by the reference. The reference to a Recordset is actually a reference to a subset of the child, called a chapter. A single parent can reference more than one child Recordset.
ADO support for data shaping enables you to query a data source and return a Recordset in which a (parent) record represents a (child) Recordset. In the customer-order scenario, you can use data shaping to retrieve customers' information as well as the orders placed by each customer in a single query. The resultant Recordset is also known as shaped Recordset.
In addition, data shaping in ADO allows you to create new Recordset objects without an underlying data source by using the NEW keyword to describe the fields of the parent and child Recordsets. The new Recordset object can then be populated with data and persistently stored. Developers can also perform various calculations or aggregations (for example, SUM, AVG, and MAX) on child fields. Data shaping can also create a parent Recordset from a child Recordset by grouping records in the child and placing one row in the parent for each group in the child.
Regular SQL allows you to retrieve data using JOIN syntax, but this can be inefficient and unwieldy because redundant parent data is repeated in each record returned for a given parent-child relationship. Data shaping can relate a single parent record in the parent Recordset to multiple child records in the child Recordset, avoiding the redundancy of a JOIN. Most people find the parent-child multiple Recordset programming model more natural and easier to work with than the single Recordset JOIN model.