内部联接3张桌子后无法获得结果

Question

I have declare a List<Object[]> which returning list of object array, where each array represents a row in result. And index of values are based on your select statement.

productList = 
(List<Object[]>) session.createSQLQuery("
SELECT User.username, User.email, Orders.p_id, Orders.o_id, Product.listed_price " +                                                                                         
"FROM Orders " +                                                                     
"INNER JOIN User ON User.u_id = Orders.u_id " +                                                                  
"INNER JOIN Product ON Product.p_id = Orders.p_id " +                                                                
"WHERE Product.p_id = '"+p_id +"' " +                                                            
"ORDER BY User.username").list();

I have 3 tables User, Product and Orders .

USER:
-----+-----------+------------+---------+----------+-----------+
 u_id | username  | password   | contact | email   | city      |
------+-----------+------------+---------+---------+-----------+

PRODUCT:
+------+----------+--------------+------+--------------+
| p_id | category | listed_price | qty  | description  |
+------+----------+--------------+------+--------------+

ORDERS:
+------+--------+------+------+-----------+
| o_id | date   | u_id | p_Id | order_qty |
+------+--------+------+------+-----------+

I wants to Inner joins User table with Product along with o_id (from ORDER) in below order:

+-----------+-------+------+------+--------------+
| username  | email | p_id | o_id | listed_price |
+-----------+-------+------+------+--------------+

In my ActionClass/View class i declare public List<Object[]> productList; to access object list from controller class above.

public List<Object[]> productList;

public String listAllProduct(){
        HttpServletRequest request = (HttpServletRequest) ActionContext.getContext().get(ServletActionContext.HTTP_REQUEST);
        productList = orderDaoFactory.listProduct(Integer.parseInt( request.getParameter("p_id"))); 
         System.out.println("\t"+productList.get(0).toString());
        return SUCCESS;
}

In my JSP page i'm using this list (array of object) productList as an Iterator tag to iterate all customers who have ordered that product.

<s:iterator value="productList">

        <tr>
            <td><h4><s:property value="username"/></h4></td>    
            <td><h4><s:property value="email"/></h4></td>
            <td><h4><s:property value="p_id"/></h4></td>
            <td><h4><s:property value="o_id"/></h4></td>
            <td><h4><s:property value="listed_price"/></h4></td>            
        </tr>

</s:iterator>

Challenges/Issues: My problem is not to get output successfully even not getting any error after debugging. Empty mind now thinking to use O/R mapping to associate Objects JOIN with others. Please suggest me where i am wrong. Your suggestions appreciable.

Answer 1

productList = 
(List<Object[]>) session.createSQLQuery("
SELECT User, Orders, Product" +                                                                                         
"FROM User,Orders,Product " +                                                                     
"INNER JOIN User ON User.u_id = Orders.u_id " +                                                                  
"INNER JOIN Product ON Product.p_id = Orders.p_id " +                                                                
"WHERE Product.p_id = '"+p_id +"' " +                                                            
"ORDER BY User.username").list();
Then you will get three object. In first list you will get Object[0]=Users,Object[1]=Orders,Object[2]=Product. Now iterate it. 

after edition

productList = 
(List<Object[]>) session.createQuery("
SELECT User, Orders, Product" +                                                                                         
"FROM User,Orders,Product " +                                                                     
"INNER JOIN User ON User.u_id = Orders.u_id " +                                                                  
"INNER JOIN Product ON Product.p_id = Orders.p_id " +                                                                
"WHERE Product.p_id = '"+p_id +"' " +                                                            
"ORDER BY User.username").list();

what is the problem with is syntax??

Answer 2

Use HQL instead of SQL if you want to query your objects directly. Use session.createQuery(String) with the following query :

SELECT u.username, u.email, o.p_id, o.o_id, p.listed_price FROM Orders as o
INNER JOIN User as u WITH u.u_id = o.u_id
INNER JOIN Product as p WITH p.p_id = o.p_id
WHERE p.p_id = ???
ORDER BY u.username