Quadcap Embeddable Database

com/quadcap/sql/StmtDropConstraint.java

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package com.quadcap.sql;

/* Copyright 1999 - 2003 Quadcap Software.  All rights reserved.
 *
 * This software is distributed under the Quadcap Free Software License.
 * This software may be used or modified for any purpose, personal or
 * commercial.  Open Source redistributions are permitted.  Commercial
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 * this software requires a "Commercial Redistribution License"; see
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 *    irrevocable offer to provide a copy of the Source Code for up to three
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import java.io.IOException;

import java.util.Enumeration;

import java.sql.SQLException;

import com.quadcap.util.Debug;

/**
 * Implementation of the SQL <B>DROP CONSTRAINT</B> statement. 
 *
 * @author Stan Bailes
 */
public class StmtDropConstraint implements Stmt {
    String                              tableName;
    String                              constraintName;
    boolean                             restrict;

    public StmtDropConstraint(String tableName, String constraintName,
                              boolean restrict) {
        this.tableName = tableName;
        this.constraintName = constraintName;
        this.restrict = restrict;
    }

    public void execute(Session session) throws IOException, SQLException {
        session.getTableWriteLock("#Schema");
        session.getTableWriteLock(tableName);
        Database db = session.getDatabase();
        Table table = (Table)db.getRelation(tableName);
        if (table == null) {
            throw new SQLException("table not found: " + tableName);
        }
        Constraint constraint = table.getConstraint(constraintName);
        if (constraint == null) {
            throw new SQLException("constraint not found: " + constraintName);
        }
        if (restrict) {
            if (constraint instanceof UniqueConstraint) {
                UniqueConstraint uc = (UniqueConstraint)constraint;
                Enumeration en = uc.getExportConstraints();
                if (en.hasMoreElements()) {
                    throw new SQLException("Can't drop unique/primary key " +
                                           "because of referencing foreign " +
                                           "key constraints");
                }
            }
        } else {
            if (constraint instanceof UniqueConstraint) {
                UniqueConstraint uc = (UniqueConstraint)constraint;
                Enumeration en = uc.getExportConstraints();
                while (en.hasMoreElements()) {
                    String name = (String)en.nextElement().toString();
                    ExportedKeyConstraint ec = 
                        (ExportedKeyConstraint)table.getConstraint(name);
                    session.doStep(new DeleteConstraint(session, table, ec));
                    DeleteConstraint.deleteForeign(session, ec);
                }
            }
        }

        // --- if we're about to delete the last unique/primary key constraint,
        // --- we have to create a DefaultTableConstraint so there's some
        // --- kind of index.
        if (constraint instanceof IndexConstraint) {
            int icnt = 0;
            int num = table.getNumConstraints();
            for (int i = 0; i < num; i++) {
                Constraint c = table.getConstraint(i);
                if (c instanceof IndexConstraint) icnt++;
            }
            if (icnt == 1) {
                DefaultTableConstraint con = new DefaultTableConstraint();
                con.setTable(table);
                table.nameConstraint(con);
                session.doStep(new AddConstraint(session, table, con));
            }
        }
        session.doStep(new DeleteConstraint(session, table, constraint));
        DeleteConstraint.deleteForeign(session, constraint);

    }

}