1 The SQL-ODBC Library

1.5 Result-set collections

A result-set collection, in spirit, contains the result of an SQL SELECT statement. To provide these results, result-set collections and their methods control the retrieval of elements from the database. Each element of a result set is a record and each element of a record is a value. The SQL-ODBC library does not provide any classes to represent columns; the elements of a record are just Dylan objects.

Result-set classes, in conjunction with the methods defined on them, provide a protocol to retrieve data from a database. Result-sets do not necessarily contain the records from the database. A result set could cache a small subset of the records retrieved for performance reasons. The logic for retrieving a record from a result set (from the database) is as follows:

: 1. Perform an internal fetch: values are stored into bindings established during SQL statement preparation. A record object is created during the preparation of the SQL statement which represents the values of the record (collection of values).
: 2. Invoke the liaison method on the record object. The result of the liaison function is the result of the collection access.

The columns of a record are processed when the columns are retrieved from the record object. This includes checking for null values and performing data coercion if a coercion-policy is supplied.