Data Access Library for Eiffel contents structure

FIELD

An object of this class describes TABLE' s or RECORDSET's column. At the same time it is intended to store values of some predefined types: INTEGER, REAL, DOUBLE, BOOLEAN, CHARACTER, STRING, DATETIME or BLOB.

The features of this class can be divided into three logic groups. The column attributes - name, table_name, type, is_required, etc. comprise the first group.

Second group is presented by features for storing and retrieving of a value and its current state: put, item, set_null and is_null. Besides there are some special features plus, plus_real, minus_double, etc., which simplify the code in some typical situations.

Features of the third group are to_integer, to_string, etc., that allow easy and elegant conversion among data types. For example, two following examples do the same - obtain an integer value from the field field:

field: FIELD

A.

ir: INTEGER_REF
n: INTEGER
...
ir ?= field.item
n := ir.item

B.

n: INTEGER
...
n := field.to_integer

A cross type conversion is also permitted. For example, having the INTEGER field you can expose the value via to_string, to_boolean, to_real, to_double and to_character, along with to_integer.

Usage of this class is shown in examples for RECORDSET and DB_TABLE.


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Last updated: 2005/02/02 11:51:24