# Configure trade-model cache fields

In this tutorial we will look at configuring and using cache fields with a simplified trade model. In Trading Integration Adapter blades, the _trademodels.xml_ file located in _Blade/DataSource/etc_ specifies the various states and transitions that govern the lifecycle of a trade.

## Overview

On receiving a client side [TradeEvent,opts="nofollow"](https://docs.caplin.com/developer/api/cis/6/com/caplin/trading/TradeEvent.html), a trade is promoted to another state and the `TradeEvent` is then forwarded to a registered [TradeListener,opts="nofollow"](https://docs.caplin.com/developer/api/cis/6/com/caplin/trading/TradeListener.html) (the generated <tradeModel name>TradeListenerAdapter), here the type is parsed and the event is sent out to the appropriate method on the < tradeModel name >TradeListener. In the implementation of this < tradeModel name >TradeListener, the trade can be obtained from the event and its cached fields' values can be extracted from the `TradeEvent` to be put onto the desired new <trigger>TradeEvent to be sent in response.

## Example

So here’s an example using the following simplified trade model:

![cis_simplified_trade_model](../../../images/cis_simplified_trade_model.png)

```xml
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<tradeModels>
     <tradeModel initialState="Initial" name="ESP">
          <cacheFields>
               <cacheField name="RequestID" where="server"/>
               <cacheField name="TradeDetails" where="server"/>
          </cacheFields>
          <state name="Initial">
               <transition source="client" target="Processing" trigger="Open">
                    <field description="Request ID" name="RequestID" required="true"/>
                    <field description="Request Time" name="RequestTime" required="true"/
                    <field description="Trade Details" name="TradeDetails" required="true"/>
               </transition>
          </state>
          <state name="Processing">
               <transition source="server" target="Confirmed" trigger="Confirmation">
                    <field description="Request ID" name="RequestID" required="true"/>
                    <field description="Confirmation ID" name="ConfirmationID" required="true"/>
                    <field description="Confirmation Time" name="ConfirmationTime" required="true"/>
               </transition>
          </state>
          <state name="Confirmed"/>
          <designer>
               <stateAttr name="Initial" visible="true" x="275" y="42"/>
               <stateAttr name="Processing" visible="true" x="275" y="162"/>
               <stateAttr name="Confirmed" visible="true" x="275" y="300"/>
          </designer>
     </tradeModel>
</tradeModels>
```

```java
public class SimpleBackend implements ESPTradeListener
{
    …

    @Override
    public void onOpen(OpenTradeEvent event )
    {
        ProcessingResponder responder = trade.getProcessingResponder();
        ConfirmationTradeEvent confirmationEvent = new ConfirmationTradeEvent(trade);

        // Copy all cached fields to outgoing message
        for (Map.Entry<String, String> field :trade.getFields().entrySet())
        { 
            confirmationEvent.addField(field.getKey(), field.getValue());
        }

        // Set transition specific fields                                
        confirmationEvent.setConfirmationID(String.valueOf(nextConfirmationID++));            
        confirmationEvent.setConfirmationTime(String.valueOf(System.currentTimeMillis()));

        // Send the confirmation
        try
        {
            responder.sendConfirmationEvent(confirmationEvent);                    
        }
        catch (TradeException e)
        {
            e.printStackTrace();
        }
    }

    …
}
```

The `OpenTradeEvent` with which the `onOpen` method is called, in the `ESPTradeListener` implementation (above), will contain a trade with only the `RequestId` and `TradeDetails` cached. Therefore only those two fields will be transferred to the `ConfirmationEvent` by the for loop and `TradeTime` will not be accessible.

## CacheField Options

When no `cacheFields` tag is present, all fields will be cached as before. If no `cacheField` tags are present within cacheFields, no fields will be cached. Each cacheField tag must have the attributes `name` and `where`:

```xml
<cacheField name="TradeDetails" where="server"/>
```

The attribute `where` can have one of three values:

* server
* client
* both