keydef.java

Town是一个100% 纯Java API

package com.workingdogs.town;

import java.util.Vector;

/*
Town, a Java JDBC abstraction layer
Copyright (C) 1999  Serge Knystautas, Jon S. Stevens

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the
Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA  02111-1307, USA.
*/
/**
A KeyDef is a way to define the key columns in a table. The KeyDef is
generally used in conjunction with a <a href="TableDataSet.html">TableDataSet</a>.
Essentially a KeyDef is what forms the WHERE clause for an UPDATE or DELETE.
<P>
In order to use the KeyDef, you simply use it like this:
<PRE>
KeyDef kd = new KeyDef().addAttrib("key_column_a");
TableDataSet tds = new TableDataSet ( connection, "table", kd );
Record rec = tds.getRecord(0);
rec.setValue("column_name", "new value" );
rec.save();
tds.close();
</PRE>
In the above example, Record 0 is retrieved from the database table
and the following update statement is generated:
<P>
UPDATE table SET column_name=? WHERE key_column_a=?
<P>

@author Jon S. Stevens <A HREF="mailto:[e-mail]">[e-mail]</A>
@author Serge Knystautas <a href="mailto:[e-mail]">[e-mail]</a>
@version 1.0
*/
public class KeyDef
{
    Vector data = new Vector ();
    public KeyDef()
    {
        super();
        // KeyDef is 1 based.
        data.addElement ("");
    }
    /**
        Adds the named attribute to the KeyDef.

        @returns a copy of itself
      */
    public KeyDef addAttrib(String name)
    {
        data.addElement (name);
        return this;
    }
    /**
        Determines if the KeyDef contains the requested Attribute.

        @returns true if the attribute has been defined. false otherwise.
      */
    public boolean containsAttrib (String name)
    {
        return !(data.indexOf ((Object) name) == -1);
    }
    /**
        getAttrib is 1 based. Setting pos to 0 will attempt to return pos 1.

        @returns value of Attribute at pos as String. null if value is not found.
      */
    public String getAttrib (int pos)
    {
        if (pos == 0)
            pos = 1;

        try
        {
            return (String) data.elementAt (pos);
        }
        catch (ArrayIndexOutOfBoundsException e)
        {
            return null;
        }
    }
    /**
        KeyDef's are 1 based, so this overrides the Vector.size() method and
        returns size - 1;

        @returns the number of elements in the KeyDef that were set by addAttrib()
        @see #addAttrib(java.lang.String)
      */
    public int size()
    {
        return data.size() - 1;
    }
}