com.sas.storage.jdbc
Class JDBCRowCountAdapter

com.sas.storage.jdbc.JDBCRowCountAdapter

All Implemented Interfaces:

com.sas.table.StaticColumnInfoInterface, com.sas.util.transforms.DisplayTransformInterface

Direct Known Subclasses:

JDBCToTableModelAdapter

public abstract class JDBCRowCountAdapter

In many cases it may not be necessary or may be an expensive operation to determine the true row count of a data source. For example, one way to calculate the true row count of a forward only result set is to increment a counter while calling next() on the result set until the end of the result set is reached. This could be inefficient for large result sets.

This class optionally provides an alternative way for calculating the row count, by calculating a "current maximum row count". This value, specified by the currentMaxRowCount property is calculated in the calculateCurrentMaxRowCount method by advancing the result set cursor ahead of the input specified row, or the currentMaxRowCount, whichever is greater. The amount the cursor will be advanced is specified by the readAheadAmount property. The default read ahead amount is 50 rows. When the end of the result set is reached, the maxRowsFound property is set to true, and the currentMaxRowCount is equal to the true row count.

Field Summary

protected int	currentMaxRowCount The current number of rows that have been read from the data source
protected boolean	maxRowsFound A flag indicating if the true row count has been determined
static java.lang.String	RB_KEY
protected static int	READ_AHEAD_AMOUNT The default number of row to read ahead in the result set
protected int	readAheadAmount The number of rows to read ahead in the data source
protected boolean	trueRowCountCalculated If true, the actual row count is calculated.

Fields inherited from class com.sas.storage.jdbc.JDBCAdapter

autoCommit, CLASS_NAME, columnInfoUsed, conn, designTime, displayTransform, forwardOnly, initialized, isRowCountKnown, LABEL, meta, NAME, printWarnings, queryRowCountDisabled, queryStatement, readOnly, result, resultSetRequeryUsed, resultSetType, resultSetUsed, retrieveNumericTypesAsDouble, rowCount, rowCountQueryString, rowNumber, spcs, stmt, trimUsed

Constructor Summary

JDBCRowCountAdapter()
Default constructor called when the adapter is made in a webAF project.

JDBCRowCountAdapter(java.sql.Connection conn, java.lang.String queryStatement)
Constructor used to create an initialized adapter.

JDBCRowCountAdapter(java.sql.ResultSet result)
Constructor used to connect an adapter directly to a previously created ResultSet.

Method Summary

protected void	calculateCurrentMaxRowCount(int requestedRow) Calculates the currentMaxRowCount by attempting to advance the result set cursor ahead of the requestedRow or currentMaxRowCount, whichever is greater.
protected abstract void	fireModelInsertEvent(int startRow, int endRow) Fire a insert event for a model signaling that an insert has occurred.
int	getReadAheadAmount() Returns the number of rows the adapter will read ahead in the result set.
boolean	isTrueRowCountCalculated() Returns true if the true row count is calcualted.
void	setConnection(java.sql.Connection conn) Sets the connection object on the adapter.
void	setQueryStatement(java.lang.String queryStatement) The queryStatement should be any SQL query that is valid for the JDBC data source.
void	setReadAheadAmount(int readAheadAmount) Sets the amount of rows that the adapter will attempt to read ahead in the result set.
void	setTrueRowCountCalculated(boolean trueRowCountCalculated) Sets whether to calculate the true row count or the current maximum row count.

Methods inherited from class com.sas.storage.jdbc.JDBCAdapter

addPropertyChangeListener, addPropertyChangeListener, calculateRowCount, close, doAbsolute, doCountColumns, doUpdateCell, finalize, fireCellEvent, fireModelEvent, fireModelEvent, getAutoCommit, getColumnInfo, getColumnInfoNames, getConnection, getDisplayTransform, getModel, getPrintWarnings, getQueryStatement, getResultSetConcurrency, getResultSetRowCount, getResultSetType, getRowCountByCountFunction, getRowCountQueryString, init, initializeData, isQueryRowCountDisabled, isReadOnly, isResultSetRequeryUsed, isRetrieveNumericTypesAsDouble, isTrimUsed, printSQLWarning, putColumnInfoUsed, putValueAt, refresh, removePropertyChangeListener, removePropertyChangeListener, retrieveColumnClass, retrieveColumnCount, retrieveColumnIndex, retrieveColumnInfoUsed, retrieveColumnLabel, retrieveValueAt, retrieveValueAt, setAutoCommit, setDisplayTransform, setModel, setPrintWarnings, setQueryRowCountDisabled, setReadOnly, setResultSetRequeryUsed, setResultSetType, setRetrieveNumericTypesAsDouble, setRowCountQueryString, setTrimUsed

Field Detail

RB_KEY

public static final java.lang.String RB_KEY

See Also:

Constant Field Values

maxRowsFound

protected boolean maxRowsFound

A flag indicating if the true row count has been determined

currentMaxRowCount

protected int currentMaxRowCount

The current number of rows that have been read from the data source

readAheadAmount

protected int readAheadAmount

The number of rows to read ahead in the data source

trueRowCountCalculated

protected boolean trueRowCountCalculated

If true, the actual row count is calculated. If false, the currentMaxRowCount value will attempt to be at least the readAheadAmount number of rows higher than the highest row number retrieved.

READ_AHEAD_AMOUNT

protected static final int READ_AHEAD_AMOUNT

The default number of row to read ahead in the result set

See Also:

Constant Field Values

Constructor Detail

JDBCRowCountAdapter

public JDBCRowCountAdapter()

Default constructor called when the adapter is made in a webAF project.

JDBCRowCountAdapter

public JDBCRowCountAdapter(java.sql.ResultSet result)

Constructor used to connect an adapter directly to a previously created ResultSet. In order for the adapter to work properly, the ResultSet should be scrollable.

Parameters:

result - ResultSet to use.

JDBCRowCountAdapter

public JDBCRowCountAdapter(java.sql.Connection conn,
                           java.lang.String queryStatement)

Constructor used to create an initialized adapter.

Parameters:

conn - A java.sql.Connection object.

queryStatement - A SQL query that is valid for the database represented by conn.

Method Detail

setTrueRowCountCalculated

public void setTrueRowCountCalculated(boolean trueRowCountCalculated)

Sets whether to calculate the true row count or the current maximum row count. The default is false.

The current maximum row count is calculated by attempting to read ahead in the result set by readAheadAmount rows when a value is retrieved. When the end of the result set is reached the current max row count is equal to the true row count and the maxRowsFound is set to true.

Parameters:

trueRowCountCalculated - true if the true row count should be calculated, false if the current maximum row count should be calculated

See Also:

isTrueRowCountCalculated()

isTrueRowCountCalculated

public boolean isTrueRowCountCalculated()

Returns true if the true row count is calcualted. Returns false if the current maximum row count is calculated.

See Also:

setTrueRowCountCalculated(boolean)

getReadAheadAmount

public int getReadAheadAmount()

Returns the number of rows the adapter will read ahead in the result set.

See Also:

setReadAheadAmount(int)

setReadAheadAmount

public void setReadAheadAmount(int readAheadAmount)

Sets the amount of rows that the adapter will attempt to read ahead in the result set. If this value is not greater than 0 an IllegalArgumentException is thrown. The default value is 50.

Parameters:

readAheadAmount - the number of rows the adapter will read ahead in the result set

See Also:

getReadAheadAmount()

calculateCurrentMaxRowCount

protected void calculateCurrentMaxRowCount(int requestedRow)
                                    throws java.sql.SQLException

Calculates the currentMaxRowCount by attempting to advance the result set cursor ahead of the requestedRow or currentMaxRowCount, whichever is greater. The amount the cursor will be advanced is specified by the readAheadAmount property. When the end of the result set is found, the maxRowsFound property is set to true.

Parameters:

requestedRow - the row number to read ahead of

Throws:

java.sql.SQLException

setQueryStatement

public void setQueryStatement(java.lang.String queryStatement)

The queryStatement should be any SQL query that is valid for the JDBC data source. It is used to extract the desired data from the database.

Calling this method has no affect if the constructer taking a ResultSet was used to create the adapter and the ResultSet is not a RowSet.

Overrides:

setQueryStatement in class JDBCAdapter

Parameters:

queryStatement - The SQL query to apply.

setConnection

public void setConnection(java.sql.Connection conn)

Sets the connection object on the adapter.

Overrides:

setConnection in class JDBCAdapter

Parameters:

conn - A java.sql.Connection object.

fireModelInsertEvent

protected abstract void fireModelInsertEvent(int startRow,
                                             int endRow)

Fire a insert event for a model signaling that an insert has occurred. Subclasses must override this method to fire a default events for their model.