The standard interface that all standard implementations of
FilteredRowSet must implement. The FilteredRowSetImpl class
provides the reference implementation which may be extended if required.
Alternatively, a vendor is free to implement its own version
by implementing this interface.
1.0 Background
There are occasions when a RowSet object has a need to provide a degree
of filtering to its contents. One possible solution is to provide
a query language for all standard RowSet implementations; however,
this is an impractical approach for lightweight components such as disconnected
RowSet
objects. The FilteredRowSet interface seeks to address this need
without supplying a heavyweight query language along with the processing that
such a query language would require.
A JDBC FilteredRowSet standard implementation implements the
RowSet interfaces and extends the
CachedRowSetTM class. The
CachedRowSet class provides a set of protected cursor manipulation
methods, which a FilteredRowSet implementation can override
to supply filtering support.
2.0 Predicate Sharing
If a FilteredRowSet implementation is shared using the
inherited createShared method in parent interfaces, the
Predicate should be shared without modification by all
FilteredRowSet instance clones.
3.0 Usage
By implementing a Predicate (see example in Predicate
class JavaDoc), a FilteredRowSet could then be used as described
below.
FilteredRowSet frs = new FilteredRowSetImpl();
frs.populate(rs);
Range name = new Range("Alpha", "Bravo", "columnName");
frs.setFilter(name);
frs.next() // only names from "Alpha" to "Bravo" will be returned
In the example above, we initialize a Range object which
implements the Predicate interface. This object expresses
the following constraints: All rows outputted or modified from this
FilteredRowSet object must fall between the values 'Alpha' and
'Bravo' both values inclusive, in the column 'columnName'. If a filter is
applied to a FilteredRowSet object that contains no data that
falls within the range of the filter, no rows are returned.
This framework allows multiple classes implementing predicates to be
used in combination to achieved the required filtering result with
out the need for query language processing.
4.0 Updating a FilteredRowSet Object
The predicate set on a FilteredRowSet object
applies a criterion on all rows in a
RowSet object to manage a subset of rows in a RowSet
object. This criterion governs the subset of rows that are visible and also
defines which rows can be modified, deleted or inserted.
Therefore, the predicate set on a FilteredRowSet object must be
considered as bi-directional and the set criterion as the gating mechanism
for all views and updates to the FilteredRowSet object. Any attempt
to update the FilteredRowSet that violates the criterion will
result in a SQLException object being thrown.
The FilteredRowSet range criterion can be modified by applying
a new Predicate object to the FilteredRowSet
instance at any time. This is possible if no additional references to the
FilteredRowSet object are detected. A new filter has has an
immediate effect on criterion enforcement within the
FilteredRowSet object, and all subsequent views and updates will be
subject to similar enforcement.
5.0 Behavior of Rows Outside the Filter
Rows that fall outside of the filter set on a FilteredRowSet
object cannot be modified until the filter is removed or a
new filter is applied.
Furthermore, only rows that fall within the bounds of a filter will be
synchronized with the data source.
author:
Jonathan Bruce |