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package liquibase.statement;

import liquibase.Scope;
import liquibase.change.ColumnConfig;
import liquibase.change.core.LoadDataColumnConfig;
import liquibase.changelog.ChangeSet;
import liquibase.database.Database;
import liquibase.exception.DatabaseException;
import liquibase.logging.Logger;
import liquibase.resource.ResourceAccessor;

import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

/**
 * Performance-optimised version of {@link ExecutablePreparedStatementBase}. JDBC batching collects several
 * executions of DML statements and waits until a certain number of commands has been collected. Then, it sends all
 * of them to the RDBMS in a single call. {@link java.sql.Statement#executeBatch()} saves many round-trips between
 * client and database, often speeding up bulk inserts/updates dramatically if the JDBC driver supports it.
 * @see 
 *     Blog entry on "Java Persistence Performance" about batching
 */
public class BatchDmlExecutablePreparedStatement extends ExecutablePreparedStatementBase {
    private final List collectedStatements;
    private final Logger LOG = Scope.getCurrentScope().getLog(getClass());

    public BatchDmlExecutablePreparedStatement(
            Database database, String catalogName, String schemaName, String tableName,
            List columns, ChangeSet changeSet, ResourceAccessor resourceAccessor,
            List statements) {
        super(database, catalogName, schemaName, tableName, new ArrayList(columns), changeSet,
            resourceAccessor);
        this.collectedStatements = new ArrayList<>(statements);
    }

    /**
     * Returns the individual statements that are currently store in this batch.
     * @return the List of the stored statements (may be empty if none are stored)
     */
    public List getIndividualStatements() {
        return new ArrayList<>(collectedStatements);
    }

    @Override
    protected void attachParams(List ignored, PreparedStatement stmt)
            throws SQLException, DatabaseException {
        for (ExecutablePreparedStatementBase insertStatement : collectedStatements) {
            super.attachParams(insertStatement.getColumns(), stmt);
            stmt.addBatch();
        }
    }

    @Override
    protected String generateSql(List cols) {
        // By convention, all of the statements are the same except the bind values. So it is sufficient to simply
        // return the first collected statement for generation.
        return collectedStatements.get(0).generateSql(cols);
    }

    @Override
    protected void executePreparedStatement(PreparedStatement stmt) throws SQLException {
        int[] updateCounts = stmt.executeBatch();
        long sumUpdateCounts = 0;
        for (int updateCount : updateCounts) {
            sumUpdateCounts = updateCount;
        }
        LOG.info(String.format("Executing JDBC DML batch was successful. %d operations were executed, %d individual UPDATE events were confirmed by the database.",
                updateCounts.length, sumUpdateCounts));
    }

    @Override
    public boolean continueOnError() {
        return false;
    }
}