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package oracle.toplink.essentials.internal.helper;
import java.sql.*;
import java.util.*;
import oracle.toplink.essentials.internal.expressions.SQLSelectStatement;
import oracle.toplink.essentials.internal.expressions.ForUpdateClause;
import oracle.toplink.essentials.queryframework.*;
import oracle.toplink.essentials.expressions.Expression;
import oracle.toplink.essentials.internal.sessions.AbstractSession;
import oracle.toplink.essentials.internal.databaseaccess.DatabaseCall;
import oracle.toplink.essentials.internal.databaseaccess.Accessor;
/**
* INTERNAL:
* <p><b>Purpose</b>:LOBValueWriter is used to write a large size of object into an Oracle
* CLOB/BLOB column through Oracle LOB Locator. It's a work-around object for the well-known 4k write
* limits on an Oracle thin driver.
*
* <p><b>Responsibilities</b>:<ul>
* <li> Build the Oracle empty lob method call string for the insert call.
* <li> Build the minimial SELECT call to retrieve the locator.
* <li> Write the lob value through the locator.
* <li> Resolve the multiple table INSERT/SELECT orders.
* <li> Resolve the nested unit of work commit issue.
* </ul>
*
* @author: King Wang
* @since TopLink/Java 5.0. July 2002.
*/
public class LOBValueWriter {
//DatabaseCalls still to be processed
private Collection calls = null;
private Accessor accessor;
/**
* This is the default constructor for the class.
*
* Bug 2804663 - Each DatabaseAccessor will now hold on to its own instance
* of this class, hence a singleton pattern is not applicable.
*/
public LOBValueWriter(Accessor accessor) {
this.accessor = accessor;
}
protected void buildAndExecuteCall(DatabaseCall dbCall, AbstractSession session) {
DatabaseQuery query = dbCall.getQuery();
if (!query.isWriteObjectQuery()) {
//if not writequery, should not go through the locator writing..
return;
}
WriteObjectQuery writeQuery = (WriteObjectQuery)query;
writeQuery.setAccessor(accessor);
//build a select statement form the query
SQLSelectStatement selectStatement = buildSelectStatementForLocator(writeQuery, dbCall, session);
//then build a call from the statement
DatabaseCall call = buildCallFromSelectStatementForLocator(selectStatement, writeQuery, dbCall, session);
accessor.executeCall(call, call.getQuery().getTranslationRow(), session);
}
/**
* Fetch the locator(s) from the result set and write LOB value to the table
*/
public void fetchLocatorAndWriteValue(DatabaseCall dbCall, Object resultSet) throws SQLException {
Enumeration enumFields = dbCall.getContexts().getFields().elements();
Enumeration enumValues = dbCall.getContexts().getValues().elements();
AbstractSession executionSession = dbCall.getQuery().getSession().getExecutionSession(dbCall.getQuery());
while (enumFields.hasMoreElements()) {
DatabaseField field = (DatabaseField)enumFields.nextElement();
Object value = enumValues.nextElement();
//write the value through the locator
executionSession.getPlatform().writeLOB(field, value, (ResultSet)resultSet, executionSession);
}
}
/**
* Build the select statement for selecting the locator
*/
private SQLSelectStatement buildSelectStatementForLocator(WriteObjectQuery writeQuery, DatabaseCall call, AbstractSession session) {
SQLSelectStatement selectStatement = new SQLSelectStatement();
Vector tables = writeQuery.getDescriptor().getTables();
selectStatement.setTables(tables);
//rather than get ALL fields from the descriptor, only use the LOB-related fields to build the minimal SELECT statement.
selectStatement.setFields(call.getContexts().getFields());
//the where clause setting here is sufficient if the object does not map to multiple tables.
selectStatement.setWhereClause(writeQuery.getDescriptor().getObjectBuilder().buildPrimaryKeyExpressionFromObject(writeQuery.getObject(), session));
//need pessimistic locking for the locator select
selectStatement.setLockingClause(ForUpdateClause.newInstance(ObjectBuildingQuery.LOCK));
if (tables.size() > 1) {
//the primary key expression from the primary table
Expression expression = selectStatement.getWhereClause();
//additioanl join from the non-primary tables
Expression additionalJoin = (Expression)writeQuery.getDescriptor().getQueryManager().getAdditionalJoinExpression();
if (additionalJoin != null) {
expression = expression.and(additionalJoin);
}
//where clause now contains extra joins across all tables
selectStatement.setWhereClause(expression);
}
//normalize the statement at the end, such as assign alias to all tables, and build sorting statement
selectStatement.normalize(session, writeQuery.getDescriptor());
return selectStatement;
}
/**
* Build the sql call from the select statement for selecting the locator
*/
private DatabaseCall buildCallFromSelectStatementForLocator(SQLSelectStatement selectStatement, WriteObjectQuery writeQuery, DatabaseCall dbCall, AbstractSession session) {
DatabaseCall call = selectStatement.buildCall(session);
//the LOB context must be passed into the new call object
call.setContexts(dbCall.getContexts());
//need to explictly define one rwo return, otherwise, TL assumes multiple rows return and confuses the accessor
call.returnOneRow();
//the query object has to be set in order to access to the platform and login objects
call.setQuery(writeQuery);
// prepare it
call.prepare(session);
//finally do the translation
call.translate(writeQuery.getTranslationRow(), writeQuery.getModifyRow(), session);
return call;
}
// Building of SELECT statements is no longer done in DatabaseAccessor.basicExecuteCall
// for updates because DatabaseCall.isUpdateCall() can't recognize update in case
// StoredProcedureCall is used. Therefore in all cases: insert(single or multiple tables)
// and update the original (insert and update) calls are saved
// and both building and executing of SELECT statements postponed until
// buildAndExecuteSelectCalls method is called.
/**
* Add original (insert or update) call to the collection
*/
public void addCall(Call call) {
if (calls == null) {
//use lazy initialization
calls = new ArrayList(2);
}
calls.add(call);
}
// Bug 3110860: RETURNINGPOLICY-OBTAINED PK CAUSES LOB TO BE INSERTED INCORRECTLY
// The deferred locator SELECT calls should be generated and executed after ReturningPolicy
// merges PK obtained from the db into the object held by the query.
// That's why original (insert or update) calls are saved,
// and both building and executing of SELECT statements postponed until
// this method is called.
/**
* Build and execute the deferred select calls.
*/
public void buildAndExecuteSelectCalls(AbstractSession session) {
if ((calls == null) || calls.isEmpty()) {
//no deferred select calls (it means no locator is required)
return;
}
//all INSERTs have been executed, time to execute the SELECTs
try {
for (Iterator callIt = calls.iterator(); callIt.hasNext();) {
DatabaseCall dbCall = (DatabaseCall)callIt.next();
buildAndExecuteCall(dbCall, session);
}
} finally {
//after executing all select calls, need to empty the collection.
//this is neccessary in the nested unit of work cases.
calls.clear();
}
}
}
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