public Class ForeignTableVTI

Overrides org.apache.derby.vti.ForwardingVTI.close.

Implements java.sql.ResultSet.close.

Doc from java.sql.ResultSet.close.

Releases this ResultSet object's database and JDBC resources immediately instead of waiting for this to happen when it is automatically closed.

The closing of a ResultSet object does not close the Blob, Clob or NClob objects created by the ResultSet. Blob, Clob or NClob objects remain valid for at least the duration of the transaction in which they are created, unless their free method is invoked.

When a ResultSet is closed, any ResultSetMetaData instances that were created by calling the getMetaData method remain accessible.

Calling the method close on a ResultSet object that is already closed is a no-op.

Exceptions

SQLException:

if a database access error occurs

This function is useful for verifying that the connection to the foreign database was dropped when the foreignViews tool was unloaded.

Returns:int

the number of open connections to foreign databases

Remove the cached connection to the foreign database. This method is called by ForeignDBViews.unloadTool().

Parameters

connectionURL:String

URL for connecting to foreign database via DriverManager.getConnection()

Implements org.apache.derby.vti.RestrictedVTI.initScan.

Doc from org.apache.derby.vti.RestrictedVTI.initScan.

Initialize a scan of a ResultSet. This method is called once before the scan begins. It is called before any ResultSet method is called. This method performs two tasks:

• Column names - Tells the ResultSet which columns need to be fetched.
• Limits - Gives the ResultSet simple bounds to apply in order to limit which rows are returned. Note that the ResultSet does not have to enforce all of these bounds. Derby will redundantly enforce these limits on all rows returned by the ResultSet. That is, filtering not performed inside the ResultSet will still happen outside the ResultSet.

The columnNames argument is an array of columns which need to be fetched. This is an array of the column names declared in the Table Function's CREATE FUNCTION statement. Column names which were double-quoted in the CREATE FUNCTION statement appear case-sensitive in this array. Column names which were not double-quoted appear upper-cased. Derby asks the Table Function to fetch all columns mentioned in the query. This includes columns mentioned in the SELECT list as well as columns mentioned in the WHERE clause. Note that a column could be mentioned in the WHERE clause in a complex expression which could not be passed to the Table Function via the restriction argument.

The array has one slot for each column declared in the CREATE FUNCTION statement. Slot 0 corresponds to the first column declared in the CREATE FUNCTION statement and so on. If a column does not need to be fetched, then the corresponding slot is null. If a column needs to be fetched, then the corresponding slot holds the column's name.

Note that even though the array may have gaps, it is expected that columns in the ResultSet will occur at the positions declared in the CREATE FUNCTION statement. Consider the following declaration:

 create function foreignEmployeeTable()
 returns table
 (
     id        int,
     birthDay  date,
     firstName varchar( 100 ),
     lastName  varchar( 100 )
 )
...

and the following query:

select lastName from table( foreignEmployeeTable() ) s

In this example, the array passed to this method will have 4 slots. Slots 0, 1, and 2 will be null and slot 3 will hold the String "LASTNAME". Last names will be retrieved from the ResultSet by calls to getString( 4 )--remember that JDBC column ids are 1-based.

The restriction argument is a simple expression which should be evaluated inside the Table Function in order to eliminate rows. The expression is a binary tree built out of ANDs, ORs, and column qualifiers. The column qualifiers are simple comparisons between constant values and columns in the Table Function. The Table Function only returns rows which satisfy the expression. The restriction is redundantly enforced by Derby on the rows returned by the ResultSet--this means that restriction gives the Table Function a hint about how to optimize its performance but the Table Function is not required to enforce the entire restriction.

Parameters

columnNames:String[]

Names of the columns to be fetched

restriction:Restriction

Where clause fragment used to filter rows

Exceptions

SQLException:

on error

Overrides org.apache.derby.vti.ForwardingVTI.isClosed.

Implements java.sql.ResultSet.isClosed.

Doc from java.sql.ResultSet.isClosed.

Retrieves whether this ResultSet object has been closed. A ResultSet is closed if the method close has been called on it, or if it is automatically closed.

Returns:boolean

true if this ResultSet object is closed; false if it is still open

Overrides org.apache.derby.vti.ForwardingVTI.next.

Implements java.sql.ResultSet.next.

Doc from java.sql.ResultSet.next.

Moves the cursor forward one row from its current position. A ResultSet cursor is initially positioned before the first row; the first call to the method next makes the first row the current row; the second call makes the second row the current row, and so on.

When a call to the next method returns false, the cursor is positioned after the last row. Any invocation of a ResultSet method which requires a current row will result in a SQLException being thrown. If the result set type is TYPE_FORWARD_ONLY, it is vendor specified whether their JDBC driver implementation will return false or throw an SQLException on a subsequent call to next.

If an input stream is open for the current row, a call to the method next will implicitly close it. A ResultSet object's warning chain is cleared when a new row is read.

Returns:boolean

true if the new current row is valid; false if there are no more rows

Exceptions

SQLException:

if a database access error occurs or this method is called on a closed result set

Table function to read a table in a foreign database.

Parameters

foreignSchemaName:String

Case-sensitive name of foreign schema

foreignTableName:String

Case-sensitive name of foreign table

connectionURL:String

URL for connecting to foreign database via DriverManager.getConnection()

Returns:ForeignTableVTI

a VTI which reads the foreign table