Mapping of composite key with both elements as foreign key

I have a simple Spring-Hibernate application. I have 3 classes crop, market and farmer with structure something like :

class crop  
{  
    private int cropId;  
}  
class market  
{   
    private int marketId;  
}  
class farmer   
{  
    private Crop crop;  
    private Market market;  
}

farmer table has a composite key{cropid, marketid}. Now, how do I map this relationship with composite key element cropid and marketid referencing to crop and market table respectively in the .hbm.xml file . I am quite new to hibernate and spring. Any suggestions will 开发者_C百科be of great help !!

---

In the farmer.hbm.xml you need to make a composite-id like this

<composite-id class="FarmerId" mapped="true">
        <key-property name="cropid"/>
        <key-property name="marketid"/>
</composite-id>

and write a class FarmerID that implements Serializable and overrides equals() and hashCode()

In equals() you test if the Objects are the same or have the same values and return a boolean. In hashCode() you generate a hash value and return it.

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if ((obj == null) || (obj.getClass() != this.getClass()))
        return false;

    FarmerID test = (FarmerID) obj;
    boolean flagCrop = cropid == test.cropid;
    boolean flagMarket = marketid == test.marketid;

    return flagCrop && flagMarket;
}

@Override
public int hashCode() {
    int hash = 7;
    hash = 31 * hash + cropid.hashCode();
    hash = 31 * hash + marketid.hashCode();
    return hash;
}