Perhaps the most obvious problem of DataTable and javax.faces.model.DataModel is lack of support for more complicated scenarios that use data from the database. To solve this problem Richfaces has two major tools:

• A set of data-driven components that render data sets in various ways (rich:dataTable , rich:dataGrid, rich:dataList, a4j:repeat etc.). All these components derive their common functionality from the common core that in addition to standard javax.faces.model.DataModel, can understand and use
• extended data model classes org.ajax4jsf.model.ExtendedDataModel and org.ajax4jsf.model.SerializableDataModel. These two classes work together to provide functions that missing in the standard DataModel.

• access for rows by primary keys instead of index position
• implementation of "visitor" pattern over the "range" of rows to support "table scroller" or "paginator" functions
• ability to serialize table data, so it can be used on post-back processing without additional database query

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<ui:composition xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://java.sun.com/jsf/facelets"
      xmlns:h="http://java.sun.com/jsf/html"
      xmlns:f="http://java.sun.com/jsf/core"
      xmlns:a4j="http://richfaces.org/a4j"
      xmlns:rich="http://richfaces.org/rich">
                
                <style type="text/css">
                    .rich-message-label {
                        color:red;
                    }
                    .col1 {
                        width:240px;
                    }
                    .col2 {
                        width:80px;
                    }
                    .col4 {
                        width:80px;
                    }
                </style>
                
                
                
                
                <h:form>
                <rich:datascroller for="auction" maxPages="5"/>
                <rich:spacer height="30" />             
                <rich:messages style="color:red"></rich:messages>
                <rich:dataTable id="auction" value="#{auctionDataModel}" columnClasses="col1,col2,col3,col4"
                                        var="item" rows="10" width="100%"> 
                    <rich:column>
                        <f:facet name="header">
                            <h:outputText value="Description"/>
                        </f:facet>
                        <h:outputText value="#{item.description}"/>
                    </rich:column>
                    <rich:column>
                        <f:facet name="header">
                            <h:outputText value="Highest Bid"/>
                        </f:facet>
                        <h:outputText id="highestBid" value="#{item.highestBid}">
                            <f:convertNumber pattern="$#,##0.00"/>
                        </h:outputText>
                    </rich:column>
                    <rich:column>
                        <f:facet name="header">
                            <h:outputText value="Your Bid"/>
                        </f:facet>
                        
                        <rich:message for="bid" /><br/>
                        <h:inputText id="bid" value="#{item.bid}" label="Bid">
                            <f:validateDoubleRange minimum="0" maximum="1000000"/>
                        </h:inputText>
                        <a4j:commandLink id="bid_link" actionListener="#{item.placeBid}" value="Place a bid!" reRender="bid,amount,highestBid" />

                    </rich:column>
                    <rich:column>
                        <f:facet name="header">
                            <h:outputText value="Amount"/>
                        </f:facet>
                        <h:outputText id="amount" value="#{item.amount}" >
                            <f:convertNumber pattern="$#,##0.00"/>
                        </h:outputText>
                    </rich:column>
                </rich:dataTable> 
                <rich:messages style="color:red"></rich:messages>
                </h:form>
</ui:composition>

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HideView AuctionDataModel.java Source

package org.richfaces.demo.extendeddatamodel;

import java.io.IOException;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.faces.application.Application;
import javax.faces.context.FacesContext;

import org.ajax4jsf.model.DataVisitor;
import org.ajax4jsf.model.Range;
import org.ajax4jsf.model.SequenceRange;
import org.ajax4jsf.model.SerializableDataModel;
/**
 * 
 * @author ias
 * This is example class that intended to demonstrate use of ExtendedDataModel and SerializableDataModel.
 * This implementation intended to be used as a request scope bean. However, it actually provides serialized
 * state, so on a post-back we do not load data from the data provider. Instead we use data that was used 
 * during rendering.
 * This data model must be used together with Data Provider, which is responsible for actual data load 
 * from the database using specific filtering and sorting. Normally Data Provider must be in either session, or conversation
 * scope.
 */
public class AuctionDataModel extends SerializableDataModel {
    
    private AuctionDataProvider dataProvider;
    private Integer currentPk;
    private Map<Integer,AuctionItem> wrappedData = new HashMap<Integer,AuctionItem>();
    private List<Integer> wrappedKeys = null;

    /**
     * 
     */
    private static final long serialVersionUID = -1956179896877538628L;

    /**
     * This method never called from framework.
     * (non-Javadoc)
     * @see org.ajax4jsf.model.ExtendedDataModel#getRowKey()
     */
    @Override
    public Object getRowKey() {
        return currentPk;
    }
    /**
     * This method normally called by Visitor before request Data Row.
     */
    @Override
    public void setRowKey(Object key) {
        this.currentPk = (Integer) key;
        
    }
    /**
     * This is main part of Visitor pattern. Method called by framework many times during request processing. 
     */
    @Override
    public void walk(FacesContext context, DataVisitor visitor, Range range, Object argument) throws IOException {
        int firstRow = ((SequenceRange)range).getFirstRow();
        int numberOfRows = ((SequenceRange)range).getRows();
        wrappedKeys = new ArrayList<Integer>();
        for (AuctionItem item:getDataProvider().getItemsByrange(new Integer(firstRow), numberOfRows, null, true)) {
            wrappedKeys.add(item.getPk());
            wrappedData.put(item.getPk(), item);
            visitor.process(context, item.getPk(), argument);
        }
    }
    /**
     * This method must return actual data rows count from the Data Provider. It is used by pagination control
     * to determine total number of data items.
     */
    private Integer rowCount; // better to buffer row count locally
    @Override
    public int getRowCount() {
        if (rowCount==null) {
            rowCount = new Integer(getDataProvider().getRowCount());
            return rowCount.intValue();
        } else {
            return rowCount.intValue();
        }
    }
    /**
     * This is main way to obtain data row. It is intensively used by framework. 
     * We strongly recommend use of local cache in that method. 
     */
    @Override
    public AuctionItem getRowData() {
        if (currentPk==null) {
            return null;
        } else {
            AuctionItem ret = wrappedData.get(currentPk);
            if (ret==null) {
                ret = getDataProvider().getAuctionItemByPk(currentPk);
                wrappedData.put(currentPk, ret);
                return ret;
            } else {
                return ret;
            }
        }
    }

    /**
     * Unused rudiment from old JSF staff.
     */
    @Override
    public int getRowIndex() {
        throw new UnsupportedOperationException();
    }

    /**
     * Unused rudiment from old JSF staff.
     */
    @Override
    public Object getWrappedData() {
        throw new UnsupportedOperationException();
    }

    /**
     * Never called by framework.
     */
    @Override
    public boolean isRowAvailable() {
        if (currentPk==null) {
            return false;
        } else {
            return getDataProvider().hasAuctionItemByPk(currentPk);
        }
    }

    /**
     * Unused rudiment from old JSF staff.
     */
    @Override
    public void setRowIndex(int rowIndex) {
        throw new UnsupportedOperationException();
    }

    /**
     * Unused rudiment from old JSF staff.
     */
    @Override
    public void setWrappedData(Object data) {
        throw new UnsupportedOperationException();
    }

    /**
     * This method suppose to produce SerializableDataModel that will be serialized into View State and used on a post-back.
     * In current implementation we just mark current model as serialized. In more complicated cases we may need to 
     * transform data to actually serialized form.
     */
    public  SerializableDataModel getSerializableModel(Range range) {
        if (wrappedKeys!=null) {
            return this; 
        } else {
            return null;
        }
    }
    
    private <V> V lookupInContext(String expression, Class<? extends V> c) {
        FacesContext facesContext = FacesContext.getCurrentInstance();
        Application application = facesContext.getApplication();
        return c.cast(application.evaluateExpressionGet(facesContext, MessageFormat.format("#'{'{0}'}'", expression), c));
    }
    
    private String auctionDataModelExpressionString;

    private String auctionDataProviderExpressionString;

    
    /**
     * This is helper method that is called by framework after model update. In must delegate actual database update to 
     * Data Provider.
     */
    @Override
    public void update() {
        AuctionDataModel auctionDataModel = lookupInContext(auctionDataModelExpressionString, AuctionDataModel.class);
        Object savedKey = getRowKey();
        for (Integer key : wrappedKeys) {
            auctionDataModel.setRowKey(key);
            auctionDataModel.getRowData().setBid(wrappedData.get(key).getBid());
        }
        setRowKey(savedKey);
        //getDataProvider().update();
        
        this.wrappedData.clear();
        this.wrappedKeys.clear();
        resetDataProvider();
    }
    
    protected void resetDataProvider() {
        this.dataProvider = null;
    }

    public AuctionDataProvider getDataProvider() {
        if (dataProvider == null) {
            dataProvider = lookupInContext(auctionDataProviderExpressionString, AuctionDataProvider.class);
        }
        return dataProvider;
    }
    public String getAuctionDataModelExpressionString() {
        return auctionDataModelExpressionString;
    }
    public void setAuctionDataModelExpressionString(
            String auctionDataModelExpressionString) {
        this.auctionDataModelExpressionString = auctionDataModelExpressionString;
    }
    public String getAuctionDataProviderExpressionString() {
        return auctionDataProviderExpressionString;
    }
    public void setAuctionDataProviderExpressionString(
            String auctionDataProviderExpressionString) {
        this.auctionDataProviderExpressionString = auctionDataProviderExpressionString;
    }

}

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