DataSourceBasedLimitResultsUtil.java

package org.pegadi.sqlsearch;

import org.apache.commons.lang.NotImplementedException;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import java.util.List;

@Component
public class DataSourceBasedLimitResultsUtil {

    private String databaseDriverName;

    public DataSourceBasedLimitResultsUtil(@Value("${server.db.driver}") String databaseDriverName) {
        this.databaseDriverName = databaseDriverName;
    }

    /**
     * @param searchTerm to decorate
     * @param numberOfRows to limit
     * @param offset rowoffset
     * @return the given SearchTerm decorated with limit and offset clause based on the database driver in use.
     * @throws NotImplementedException if handling for the database driver is implemented.
     */
    public SearchTerm createLimitClauseToSearchTerm(SearchTerm searchTerm, int numberOfRows, int offset){
        return new LimitedClauseSearchTerm(searchTerm, numberOfRows, offset);
    }

    /**
     * @param searchTerm to decorate
     * @param numberOfRows to limit
     * @return the given SearchTerm decorated with limit clause based on the database driver in use.
     * @throws NotImplementedException if handling for the database driver is implemented.
     */
    public SearchTerm createLimitClauseToSearchTerm(SearchTerm searchTerm, int numberOfRows){
        return new LimitedClauseSearchTerm(searchTerm, numberOfRows);
    }

    private String addLimitRows(String originalQuery, int numberOfRows){
        if (databaseDriverName.contains("mysql")) {
            return originalQuery + " limit " + numberOfRows;
        } else if (databaseDriverName.contains("derby")){
            return originalQuery + " fetch first " + numberOfRows + " rows only";
        } else if (databaseDriverName.contains("hsqldb")) {
            return originalQuery + " limit " + numberOfRows;
        } else {
            throw new NotImplementedException("Could not add limit clause, sqldriver " + databaseDriverName + " is unknown");
        }
    }

    private String addLimitRows(String originalQuery, int numberOfRows, int offset){
        if (databaseDriverName.contains("mysql")) {
            return originalQuery + " limit " + offset + ","  + numberOfRows;
        } else if (databaseDriverName.contains("derby")) {
            return originalQuery + " offset " + offset + " fetch next " + numberOfRows + " rows only";
        } else if (databaseDriverName.contains("hsqldb")) {
            return originalQuery + " limit " + numberOfRows + " " + offset;
        } else {
            throw new NotImplementedException("Could not add limit clause, sqldriver " + databaseDriverName + " is unknown");
        }
    }

    private class LimitedClauseSearchTerm extends SearchTerm {
        private final SearchTerm searchTerm;
        private final int numberOfRows;
        private final int offset;

        protected LimitedClauseSearchTerm(SearchTerm searchTerm, int numberOfRows) {
            this(searchTerm, numberOfRows, 0);
        }

        protected LimitedClauseSearchTerm(SearchTerm searchTerm, int numberOfRows, int offset) {
            super();
            this.searchTerm = searchTerm;
            this.numberOfRows = numberOfRows;
            this.offset = offset;
        }

        @Override
        public String whereClause() {
            return searchTerm.whereClause();
        }

        @Override
        public List<String> getTables() {
            return searchTerm.getTables();
        }

        @Override
        public List<String> getIgnoreTables() {
            return searchTerm.getIgnoreTables();
        }

        @Override
        public String getQuery(String selectString) {
            if (offset == 0) {
                return addLimitRows(searchTerm.getQuery(selectString), numberOfRows);
            } else {
                return addLimitRows(searchTerm.getQuery(selectString), numberOfRows, offset);
            }
        }

        @Override
        public void setSelectDistinct(boolean selectDistinct) {
            searchTerm.setSelectDistinct(selectDistinct);
        }
    }

}