com.blazebit.persistence.impl.dialect.MySQLDbmsLimitHandler Maven / Gradle / Ivy

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package com.blazebit.persistence.impl.dialect;

import com.blazebit.persistence.impl.function.CyclicUnsignedCounter;

import java.sql.PreparedStatement;
import java.sql.SQLException;

public class MySQLDbmsLimitHandler extends AbstractDbmsLimitHandler {

    private static final ThreadLocal threadLocalCounter = new ThreadLocal() {

        @Override
        protected CyclicUnsignedCounter initialValue() {
            return new CyclicUnsignedCounter(-1);
        }

    };

    public MySQLDbmsLimitHandler() {
        super(20);
    }

    @Override
    public boolean supportsVariableLimit() {
        return true;
    }

    /**
     * Uses a workaround for limit in IN predicates because of an limitation of MySQL.
     * See http://dev.mysql.com/doc/refman/5.0/en/subquery-restrictions.html for reference.
     *
     */
    @Override
    public void applySql(StringBuilder sqlSb, boolean isSubquery, String limit, String offset) {
        if (isSubquery) {
            // Insert it after the open bracket
            sqlSb.insert(1, "select * from (");
        }

        if (limit != null) {
            if (offset != null) {
                sqlSb.append(" limit ").append(offset).append(',').append(limit);
            } else {
                sqlSb.append(" limit ").append(limit);
            }
        } else if (offset != null) {
            // The biggest possible limit to be able to make an OFFSET only query
            sqlSb.append(" limit ").append(offset).append(",18446744073709551610");
        }

        if (isSubquery) {
            String limitSubqueryAlias = "_tmp_" + threadLocalCounter.get().incrementAndGet();
            sqlSb.append(") as ").append(limitSubqueryAlias);
        }
    }

    @Override
    public int bindLimitParametersAtEndOfQuery(Integer limit, Integer offset, PreparedStatement statement, int index) throws SQLException {
        if (limit != null) {
            if (offset != null) {
                statement.setInt(index, offset);
                statement.setInt(index + 1, limit);
                return 2;
            } else {
                statement.setInt(index, limit);
                return 1;
            }
        } else if (offset != null) {
            statement.setInt(index, offset);
            return 1;
        }

        return 0;
    }

}