| org.apache.derby.vti.DeferModification
All known Subclasses: org.apache.derby.impl.sql.compile.DefaultVTIModDeferPolicy,
| DeferModification | | public interface DeferModification (Code) | | This interface is implemented by a read/write VTI class that wants to control when
modifications to the VTI are deferred, or to be notified that a it is to be modified.
Consider the following statement:
UPDATE NEW myVTI(...)
SET cost = cost + 10
WHERE cost < 15
Updating a column that is used in the WHERE clause might or might not give the VTI implementation trouble;
the update might cause the same row to be selected more than once. This problem can be solved by building the
complete list of rows to be updated and the new column values before updating any rows. The updates are applied
after the list is built. This process is called "deferred update".
By default, updates on a VTI are deferred when the VTI ResultSet
is scrollable (ResultSet.TYPE_SCROLL_SENSITIVE or TYPE_SCROLL_INSENSITIVE), and one or more of the following is true.
- One or more of the columns in the SET clause is also used in the WHERE
clause and the VTI ResultSet is sensitive. We do not defer updates
when the ResultSet is TYPE_SCROLL_INSENSITIVE because it is not necessary.
- The where clause contains a subselect on a VTI from the same class as the
target VTI. We do not look at the VTI parameters, just the VTI class name.
By default, deletes on a VTI are deferred in a similar situation: when the VTI ResultSet
is scrollable (ResultSet.TYPE_SCROLL_SENSITIVE or TYPE_SCROLL_INSENSITIVE), and
the where clause contains a subselect on a VTI from the same class as the
target VTI. We do not look at the VTI parameters, just the VTI class name.
By default, inserts into a VTI are deferred when the same VTI class is used as both
the source and target. It does not depend on the scrollability of the
VTI ResultSet because inserts can be deferred without scrolling the ResultSet.
If these defaults are not appropriate then the class implementing the VTI should also implement
this interface (org.apache.derby.vti.DeferModification).
(A read/write VTI is implemented by a class that implements the java.sql.PreparedStatement interface,
often by extending the UpdatableVTITemplate interface. @see UpdatableVTITemplate).
Update and delete statement deferral is implemented by scrolling the VTI's ResultSet. Therefore,
updates and deletes on a VTI are never deferred unless the VTI's ResultSets are scrollable, even
if the DeferModification interface methods return true.
Therefore for an update or delete to be deferred the VTI getResultSetType() method must return
ResultSet.TYPE_SCROLL_SENSITIVE or TYPE_SCROLL_INSENSITIVE and the VTI must produce scrollable
java.sql.ResultSets that implement the getRow() and absolute() methods. If your VTI is implemented as
an extension to UpdatableVTITemplate then you must override the getResultSetMethod:
UpdatableVTITemplate.getResultSetType()
throws an exception. If your VTI's ResultSets are implemented as extensions to VTITemplate then you must
override the getRow() and absolute() methods: VTITemplate.getRow() and absolute() throw exceptions.
This interface is not used when the VTI is referenced only in a subselect; it is only used when a
VTI appears as the target of an INSERT, UPDATE, or DELETE statement.
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| Method Summary | |
| public boolean | alwaysDefer(int statementType)
This method is called during preparation of an insert, update, or delete statement with this VTI
as the target. | | public boolean | columnRequiresDefer(int statementType, String columnName, boolean inWhereClause)
This method is called during preparation of an update or delete statement on the virtual
table if getResultSetType() returns ResultSet.TYPE_SCROLL_SENSITIVE or TYPE_SCROLL_SENSITIVE and
alwaysDefer( statementType) returns false. | | public void | modificationNotify(int statementType, boolean deferred)
This VTI method is called by Cloudscape when a VTI modification (insert, update, or delete)
is executed. | | public boolean | subselectRequiresDefer(int statementType, String schemaName, String tableName)
This method is called during preparation of an insert, update, or delete statement that has this virtual
table as its target and that has a sub-select. | | public boolean | subselectRequiresDefer(int statementType, String VTIClassName)
This method is called during preparation of an insert, update, or delete statement that has this virtual
table as its target and that has a sub-select. |
| DELETE_STATEMENT | | final public static int DELETE_STATEMENT(Code) | | |
| INSERT_STATEMENT | | final public static int INSERT_STATEMENT(Code) | | |
| UPDATE_STATEMENT | | final public static int UPDATE_STATEMENT(Code) | | |
| alwaysDefer | | public boolean alwaysDefer(int statementType) throws SQLException(Code) | | This method is called during preparation of an insert, update, or delete statement with this VTI
as the target. It indicates whether the statement should be deferred irregardless of the other clauses
in the statement. If alwaysDefer returns true then the other methods in this interface
are not called. (At least not for this statement type).
Parameters:
statementType - One of INSERT_STATEMENT, UPDATE_STATEMENT, DELETE_STATEMENT. true if the statement type should always be deferred on this VTI,false other criteria (see below) should be examined to determinewhether to defer the modification.
exception:
SQLException - on an unexpected condition. |
| columnRequiresDefer | | public boolean columnRequiresDefer(int statementType, String columnName, boolean inWhereClause) throws SQLException(Code) | | This method is called during preparation of an update or delete statement on the virtual
table if getResultSetType() returns ResultSet.TYPE_SCROLL_SENSITIVE or TYPE_SCROLL_SENSITIVE and
alwaysDefer( statementType) returns false.
ColumnRequiresDefer is called once for each column that is being updated,
or each column in a DELETE where clause until
it returns true or until all the columns have been exhausted.
Parameters:
statementType - UPDATE_STATEMENT or DELETE_STATEMENT.
Parameters:
columnName - the name of one of the columns being updated
Parameters:
inWhereClause - indicates whether the column also appears in the where clause true if the update must be deferredfalse if this column does not require a deferred update
exception:
SQLException - a parameter is invalid or there is another unexpected failure. |
| modificationNotify | | public void modificationNotify(int statementType, boolean deferred) throws SQLException(Code) | | This VTI method is called by Cloudscape when a VTI modification (insert, update, or delete)
is executed. It is called after the VTI has been instantiated but before any rows are read,
inserted, updated, or deleted.
Parameters:
statementType - one of INSERT_STATEMENT, UPDATE_STATEMENT, or DELETE_STATEMENT
Parameters:
deferred - true if the modification will be deferred, false if not.
exception:
SQLException - thrown on an unexpected failure |
| subselectRequiresDefer | | public boolean subselectRequiresDefer(int statementType, String schemaName, String tableName) throws SQLException(Code) | | This method is called during preparation of an insert, update, or delete statement that has this virtual
table as its target and that has a sub-select. It is invoked once for each regular table in a sub-select,
if it has not already been determined that the statement should be deferred or that the VTI does not support
deferral.
Parameters:
statementType - the statement type: INSERT_STATEMENT, UPDATE_STATEMENT, or DELETE_STATEMENT.
Parameters:
schemaName - the schema of the table in the sub-select.
Parameters:
tableName - the name of the table in the sub-select. true if the modification must be deferredfalse if this source table does not necessitate a deferred modification
exception:
SQLException - a parameter is invalid or there is another unexpected failure. |
| subselectRequiresDefer | | public boolean subselectRequiresDefer(int statementType, String VTIClassName) throws SQLException(Code) | | This method is called during preparation of an insert, update, or delete statement that has this virtual
table as its target and that has a sub-select. It is invoked once for each virtual table in the sub-select,
if it has not already been determined that the statement should be deferred or that the VTI does not support
deferral.
Parameters:
statementType - the statement type: INSERT_STATEMENT, UPDATE_STATEMENT, or DELETE_STATEMENT.
Parameters:
VTIClassName - the name of the class implementing the VTI in the sub-select. true if the modification must be deferredfalse if this source table does not necessitate a deferred modification
exception:
SQLException - a parameter is invalid or there is another unexpected failure. |
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