帮助识别数据库实体之间的关系（用于 hibernate 映射）

Question

I have a web app in which I use hibernate and deploy on tomcat using ant.I have created a hibernate.cfg.xml in source directory with all mapping values.

My app has a ShoppingCart,CartItem and ItemForSale classes.I need to map the relation between CartItem and ItemForSale classes which are represented by database tables.I tried to work it out as shown below..I am not sure if this is the right way.. I would like your advice /opinion in this matter..Please help..

A CartItem has an ItemForSale field and quantity.

class CartItem{
    ItemForSale item;
    int quantity;
    ...
}
class ItemForSale{
    String name;
    double price;
}

Suppose I have some instances of both these classes,

saleitem1 = new ItemForSale("pizza",20.0);
saleitem2 = new ItemForSale("pastry",10.0);
saleitem3 = new ItemForSale("cake",30.0);

cartitem1 = new CartItem(saleitem1,1);
cartitem2 = new CartItem(saleitem1,2);
cartitem3 = new CartItem(saleitem2,1);

A cartitem cannot contain more than one saleitem at a time,

I have shown the mappings in a diagram below..the green lines show valid relations while red line shows an invalid relation between these two sets

From this,I deduce that,there is a many-to-one relation between CartItem and ItemForSale.So,in my CartItem.hbm.xml file,I have to write

<class name="shop.cart.CartItem" table="CARTITEM">
    <id name="cartItem_id" column="CARTITEM_ID" type="long">
        <generator class="native"/>
    </id>
    <property name="quantity" type="int" column="QUANTITY" />

    <many-to-one name="saleitem" class="shop.domain.ItemForSale" column="ITEM_FOR_SALE_ID" lazy="false" />
</class>

Is this the correct representation? Or is there something wrong with the way I worked it out?

thanks

mark

Answer 1

looks correct... you have done a unidirectional mapping...

you could also do a bidirectional mapping (doesn't change much but it gives you access to all items related to a cart.