Db.Param = new Class
({
	Extends: Vn.Param
	,Tag: 'db-param'
	,Parent: 'form'
	,Properties:
	{
		/**
		 * The form field referenced by this param.
		 **/
		column:
		{
			type: String
			,set: function (x)
			{ 
				this._columnName = x;
				this.refresh ();
			}
			,get: function ()
			{
				this._columnName;
			}
		},
		/**
		 * The form referenced by this param.
		 **/
		form:
		{
			type: Db.Form
			,set: function (x)
			{
				this.link ({_form: x},
				{
					 'status-changed': this.onFormChange
					,'iter-changed': this.onIterChange
				});

				this.refresh ();
			}
			,get: function ()
			{
				return this._form;
			}
		}
	}

	,_columnName: null
	,_form: null
	,formLock: false
	,columnIndex: -1
	
	,initialize: function (props)
	{
		this.parent (props);
		this.on ('changed', this.onChange, this);
	}
	
	,refresh: function ()
	{
		if (this._form)
		{
			this.onFormChange ();
			this.onIterChange ();
		}
	}

	,onFormChange: function ()
	{
		if (this._columnName != null)
			this.columnIndex = this._form.getColumnIndex (this._columnName);
	}

	,onIterChange: function ()
	{
		this.formLock = true;
	
		if (this.columnIndex != -1)
			this.value = this._form.getByIndex (this.columnIndex);
		else
			this.value = undefined;
		
		this.formLock = false;
	}

	,onChange: function ()
	{
		if (!this.formLock && this.columnIndex != -1)
			this._form.setByIndex (this.columnIndex, this._value);
	}
});