public class ForeignTableVTI extends ForwardingVTI implements RestrictedVTI
This class contains a table function which can be used to bulk-import data from a foreign database. Because the table function is a RestrictedVTI, it can also be used to periodically and efficiently integrate data streams from a foreign database.
If you need to siphon data out of the foreign database on an ongoing basis, you can restrict the data you SELECT. Note that the local views are backed by RestrictedVTIs. That means that the actual query sent to the foreign database will only involve the columns you SELECT. In addition, the query will include the WHERE clause, provided that it is simple enough (see the javadoc for RestrictedVTI):
The following script shows how to use this table function:
-- create a foreign database with a table in it connect 'jdbc:derby:memory:db;create=true;user=test_dbo;password=test_dbopassword'; call syscs_util.syscs_create_user( 'test_dbo', 'test_dbopassword' ); create table employee ( firstName varchar( 50 ), lastName varchar( 50 ), employeeID int primary key ); insert into employee values ( 'Billy', 'Goatgruff', 1 ); insert into employee values ( 'Mary', 'Hadalittlelamb', 2 ); connect 'jdbc:derby:memory:db;shutdown=true'; -- now create the database where we will do our work connect 'jdbc:derby:memory:db1;create=true'; -- register a table function with the shape of the foreign table create function employeeFunction ( schemaName varchar( 32672 ), tableName varchar( 32672 ), connectionURL varchar( 32672 ) ) returns table ( firstName varchar( 50 ), lastName varchar( 50 ), employeeID int ) language java parameter style derby_jdbc_result_set no sql external name 'org.apache.derby.vti.ForeignTableVTI.readForeignTable' ; -- create a convenience view to factor out the function parameters create view foreignEmployee as select firstName, lastName, employeeID from table ( employeeFunction ( 'TEST_DBO', 'EMPLOYEE', 'jdbc:derby:memory:db;user=test_dbo;password=test_dbopassword' ) ) s; -- now select from the view as though it were a local table select * from foreignEmployee; select lastName from foreignEmployee where employeeID = 2;
VTITemplate.ColumnDescriptor
CLOSE_CURSORS_AT_COMMIT, CONCUR_READ_ONLY, CONCUR_UPDATABLE, FETCH_FORWARD, FETCH_REVERSE, FETCH_UNKNOWN, HOLD_CURSORS_OVER_COMMIT, TYPE_FORWARD_ONLY, TYPE_SCROLL_INSENSITIVE, TYPE_SCROLL_SENSITIVE
Constructor and Description |
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ForeignTableVTI(String foreignSchemaName,
String foreignTableName,
Connection foreignConnection)
Construct from the foreign schema and table name and a foreign connection.
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Modifier and Type | Method and Description |
---|---|
void |
close() |
static int |
countConnections()
This function is useful for verifying that the connection to the foreign
database was dropped when the foreignViews tool was unloaded.
|
static void |
dropConnection(String connectionURL)
Remove the cached connection to the foreign database.
|
void |
initScan(String[] columnNames,
Restriction restriction)
Initialize a scan of a ResultSet.
|
boolean |
isClosed() |
boolean |
next() |
static ForeignTableVTI |
readForeignTable(String foreignSchemaName,
String foreignTableName,
String connectionURL)
Table function to read a table in a foreign database.
|
getAsciiStream, getBigDecimal, getBigDecimal, getBinaryStream, getBlob, getBoolean, getByte, getBytes, getCharacterStream, getClob, getDate, getDate, getDouble, getFloat, getInt, getLong, getMetaData, getObject, getShort, getString, getTime, getTime, getTimestamp, getTimestamp, getWrappedResultSet, wasNull, wrapResultSet
absolute, afterLast, beforeFirst, cancelRowUpdates, clearWarnings, deleteRow, findColumn, first, getArray, getArray, getAsciiStream, getBigDecimal, getBigDecimal, getBinaryStream, getBlob, getBoolean, getByte, getBytes, getCharacterStream, getClob, getConcurrency, getContext, getCursorName, getDate, getDate, getDouble, getFetchDirection, getFetchSize, getFloat, getHoldability, getInt, getLong, getNCharacterStream, getNCharacterStream, getNClob, getNClob, getNString, getNString, getObject, getObject, getObject, getObject, getObject, getRef, getRef, getReturnTableSignature, getRow, getRowId, getRowId, getShort, getSQLXML, getSQLXML, getStatement, getString, getTime, getTime, getTimestamp, getTimestamp, getType, getUnicodeStream, getUnicodeStream, getURL, getURL, getWarnings, insertRow, isAfterLast, isBeforeFirst, isFirst, isLast, isWrapperFor, last, moveToCurrentRow, moveToInsertRow, previous, refreshRow, relative, rowDeleted, rowInserted, rowUpdated, setContext, setFetchDirection, setFetchSize, unwrap, updateArray, updateArray, updateAsciiStream, updateAsciiStream, updateAsciiStream, updateAsciiStream, updateAsciiStream, updateAsciiStream, updateBigDecimal, updateBigDecimal, updateBinaryStream, updateBinaryStream, updateBinaryStream, updateBinaryStream, updateBinaryStream, updateBinaryStream, updateBlob, updateBlob, updateBlob, updateBlob, updateBlob, updateBlob, updateBoolean, updateBoolean, updateByte, updateByte, updateBytes, updateBytes, updateCharacterStream, updateCharacterStream, updateCharacterStream, updateCharacterStream, updateCharacterStream, updateCharacterStream, updateClob, updateClob, updateClob, updateClob, updateClob, updateClob, updateDate, updateDate, updateDouble, updateDouble, updateFloat, updateFloat, updateInt, updateInt, updateLong, updateLong, updateNCharacterStream, updateNCharacterStream, updateNCharacterStream, updateNCharacterStream, updateNClob, updateNClob, updateNClob, updateNClob, updateNClob, updateNClob, updateNString, updateNString, updateNull, updateNull, updateObject, updateObject, updateObject, updateObject, updateRef, updateRef, updateRow, updateRowId, updateRowId, updateShort, updateShort, updateSQLXML, updateSQLXML, updateString, updateString, updateTime, updateTime, updateTimestamp, updateTimestamp
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
updateObject, updateObject, updateObject, updateObject
public ForeignTableVTI(String foreignSchemaName, String foreignTableName, Connection foreignConnection)
Construct from the foreign schema and table name and a foreign connection.
public static ForeignTableVTI readForeignTable(String foreignSchemaName, String foreignTableName, String connectionURL)
Table function to read a table in a foreign database.
foreignSchemaName
- Case-sensitive name of foreign schemaforeignTableName
- Case-sensitive name of foreign tableconnectionURL
- URL for connecting to foreign database via DriverManager.getConnection()public static void dropConnection(String connectionURL)
Remove the cached connection to the foreign database. This method is called by ForeignDBViews.unloadTool().
public static int countConnections()
This function is useful for verifying that the connection to the foreign database was dropped when the foreignViews tool was unloaded.
public void close() throws SQLException
close
in interface AutoCloseable
close
in interface ResultSet
close
in class ForwardingVTI
SQLException
public boolean next() throws SQLException
next
in interface ResultSet
next
in class ForwardingVTI
SQLException
public boolean isClosed()
isClosed
in interface ResultSet
isClosed
in class ForwardingVTI
public void initScan(String[] columnNames, Restriction restriction) throws SQLException
RestrictedVTI
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:
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.
initScan
in interface RestrictedVTI
SQLException
Apache Derby 10.14 API Documentation - Copyright © 2004,2018 The Apache Software Foundation. All Rights Reserved.