One key to successfully using
disconnected data is minimizing the possibility for invalid
information. If invalid values are entered in the
DataSet, the error won’t be
caught until you commit changes to the data source. At this point,
the problem can be much more difficult to track down and resolve.
In order to reduce the possibility of invalid data, you can use
properties of the DataColumn object, as explained
in Chapter 8. For example, if your
DataSet is correctly configured with schema
information, you’ll receive an error if you try to
insert a null value into a
non-null column, use an invalid data type, or
exceed the column length restrictions. Another way to prevent data
errors is by using
Constraint objects.
Constraint objects are required to enforce
specialized rules that involve comparing column values in more than
one row. ADO.NET currently provides two types of constraints:
The UniqueConstraint,
which represents a rule forbidding duplicate values in a column (or
across multiple columns)
The
ForeignKeyConstraint
,
which represents a relationship that links a column (or set of
columns) in one table to a column (or set of columns) in another
table and defines the type of action to take for updates or deletions
In this chapter, you’ll learn how to create these
classes, enforce constraint checking, and enforce referential
integrity in the DataSet.