indexmgr.java

用java语言简单实现数据库的初步功能

package simpledb.index.metadata;

import static simpledb.metadata.TableMgr.MAX_NAME;
import simpledb.tx.Transaction;
import simpledb.metadata.*;
import simpledb.record.*;
import java.util.*;

/**
 * The index manager.
 * The index manager has similar functionalty to the table manager.
 * @author Edward Sciore
 */
public class IndexMgr {
	private static int nextIdxNum = 0;
	private TableInfo ti;

	/**
	 * Creates the index manager.
	 * This constructor is called during system startup.
	 * If the database is new, then the <i>idxcat</i> table is created.
	 * @param isnew indicates whether this is a new database
	 * @param tx the system startup transaction
	 */
	public IndexMgr(boolean isnew, TableMgr tblmgr, Transaction tx) {
		if (isnew) {
			Schema sch = new Schema();
			sch.addStringField("tablename", MAX_NAME);
			sch.addStringField("fieldname", MAX_NAME);
			sch.addIntField("indexnumber");
			sch.addIntField("indextype");
			tblmgr.createTable("idxcat", sch, tx);
		}
		ti = tblmgr.getTableInfo("idxcat", tx);
	}

	/**
	 * Creates an index of the specified type for the specified field.
	 * A unique ID is assigned to this index, and its information
	 * is stored in the idxcat table.
	 * @param tblname the name of the indexed table
	 * @param fldname the name of the indexed field
	 * @param idxtype the desired type of the index
	 * @param tx the calling transaction
	 */
	public void createIndex(String tblname, String fldname, int idxtype, Transaction tx) {
		int idxnum    = nextIndexNumber();
		RecordFile rf = new RecordFile(ti, tx);
		rf.insert();
		rf.setString("tablename", tblname);
		rf.setString("fieldname", fldname);
		rf.setInt("indexnumber", idxnum);
		rf.setInt("indextype", idxtype);
		rf.close();
	}

	/**
	 * Returns a map containing the index info for all indexes
	 * on the specified table.
	 * @param tblname the name of the table
	 * @param tx the calling transaction
	 * @return a map of IndexInfo objects, keyed by their field names
	 */
	public Map<String,IndexInfo> getIndexInfo(String tblname, Transaction tx) {
		Map<String,IndexInfo> result = new HashMap<String,IndexInfo>();
		RecordFile rf = new RecordFile(ti, tx);
		while (rf.next())
			if (rf.getString("tablename").equals(tblname)) {
				String fldname = rf.getString("fieldname");
				int indexnum   = rf.getInt("indexnumber");
				int idxtype    = rf.getInt("indextype");
				IndexInfo ii = new IndexInfo(tblname, fldname, indexnum,
				                             idxtype, tx);
				result.put(fldname, ii);
			}
		rf.close();
		return result;
	}

	private static synchronized int nextIndexNumber() {
		nextIdxNum++;
		return nextIdxNum;
	}
 }