ibatis-user-java mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Warren <war...@clarksnutrition.com>
Subject Re: n+1 Problem NullPointerException
Date Fri, 01 Dec 2006 23:46:06 GMT
Stefan Langer wrote:
> Warren wrote:
>> I am having problems with an n+1 sql map. I am getting the following 
>> error messages:
>>
>> --- The error occurred while applying a result map. --- Check the 
>> CatItem.catItemsResults. --- Check the result mapping for the 'items' 
>> property. --- Cause: java.lang.NullPointerException
>>
>> I have put the following test together:
>>
>> Objects
>>
>> TestCat object
>>
>> private int catPK;
>> private String catName;
>> private List items;
>>
>> TestItem object
>>
>> private int itemPK;
>> private String itemName;
>>
>> Database Tables
>>
>> testitem table
>>
>> itm_pk int4,
>> itm_cat_fk int4,
>> itm_name char(20),
>>
>> testcat table
>>
>> cat_pk int4,
>> cat_name char(20)
>>
>> <resultMap id="catItemsResults" class="testCat" groupBy="catPK" >
>>   <result property="catPK" column="cat_pk" javaType="int" 
>> jdbcType="INTEGER"/>
>>   <result property="catName" column="cat_name" javaType="string" 
>> jdbcType="CHAR"/>
>>   <result property="items" javaType="java.util.List" 
>> resultMap="CatItem.itemsResults" />
>> </resultMap>
>>   <resultMap id="itemsResults" class="testItem" >
>>  <result property="itemName" column="itm_name" javaType="string" 
>> jdbcType="CHAR"/>
>> </resultMap>
>>
>> <select id="getCatWithItems" resultMap="catItemsResults"
>>  SELECT cat_pk, cat_name, itm_name FROM testcat LEFT JOIN testitem ON 
>> cat_pk = itm_cat_fk
>> </select>
>>
>> I have looked at the FAQ, docs and mailing list archive and I can not 
>> figure out what I am doing wrong. I have tried it on a Postgres db 
>> with a postgres driver and a Sybase db with an ODBC driver. I still 
>> get the same results. I am running version 2.1.7 of Ibatis. What am I 
>> doing wrong?
>>
>> Thanks,
>>
>> Warren
> Where does the nullpointer occur? In your code or in ibatis code?
> When you run your query you will have a item in your items map even 
> though the testCat does not contain any testItem. This item will have 
> all null values. So if any of the methods in testItem throw a 
> nullpointerexception when being fed with a null value that will 
> probably be the case.
>
> I just filed an enhancement request for Ibatis to prevent ibatis from 
> creating such null objects. Feel free to vote or comment on it.
> The issue is: IBATIS-375
The null pointer occurs in:

 sqlMap.queryForList(statementName, parameterObject)

I should get a List of TestCat objects with a List of TestItems, 
shouldn't I? I couldn't quite follow your explanation of how TestCat and 
the items List are being populated. I think I understand that if a 
testCat does not have any testItems, the items List in testCat will 
still have a testItem in it with it's properties set to null, correct? 
But my query does not return any testCats without a testItem in it. My 
object setters are all very simple:

public void setCatName(String catName)
{
    this.catName = catName;
}

When I set the loggers to DEBUG I get the following log entries:

DEBUG [http-8080-Processor24] - Checked out connection 2100665 from pool.
DEBUG [http-8080-Processor24] - {conn-100186} Connection
DEBUG [http-8080-Processor24] - {pstm-100187} PreparedStatement:        
SELECT cat_pk, itm_pk, cat_name, itm_name FROM testcat LEFT JOIN 
testitem ON cat_pk = itm_cat_fk 
DEBUG [http-8080-Processor24] - {pstm-100187} Parameters: []
DEBUG [http-8080-Processor24] - {pstm-100187} Types: []
DEBUG [http-8080-Processor24] - {rset-100188} ResultSet
getBatchedItemDetails(Object batchedItems) 
EXCEPTION=com.ibatis.dao.client.DaoException: IBATIS PROBLEM Error 
executing query for list.  Cause: 
com.ibatis.common.jdbc.exception.NestedSQLException:  
--- The error occurred in 
com/clarks/spanky/persistence/sqlmapdao/sql/postgres/batchOrder-postgres.xml.  

--- The error occurred while applying a result map. 
--- Check the BatchOrder.catItemsResults. 
--- Check the result mapping for the 'items' property. 
--- Cause: java.lang.NullPointerException
Caused by: java.lang.NullPointerException
Caused by: com.ibatis.common.jdbc.exception.NestedSQLException:  
--- The error occurred in 
com/clarks/spanky/persistence/sqlmapdao/sql/postgres/batchOrder-postgres.xml.  

--- The error occurred while applying a result map. 
--- Check the BatchOrder.catItemsResults. 
--- Check the result mapping for the 'items' property. 
--- Cause: java.lang.NullPointerException
Caused by: java.lang.NullPointerException
DEBUG [http-8080-Processor24] - Returned connection 2100665 to pool.

Is this telling me that the SELECT is not returning any records? I get 
the following results when I run the above logged SELECT directly on the db:

The SELECT query returns:

** cat_pk 	cat_name 	itm_name
1 	Vitamins 	Vitamin Item 3
1 	Vitamins 	Vitamin Item 1
1 	Vitamins 	Vitamin Item 2
2 	Herbs 	Herbs Item 3
2 	Herbs 	Herbs Item 2
2 	Herbs 	Herbs Item 1
2 	Herbs 	Herbs Item 4
3 	Groceries 	Grocery Item 2
3 	Groceries 	Grocery Item 3
3 	Groceries 	Grocery Item 1


This is on a Postgres db with a postgres driver. I have also changed the 
sqlMap to the following and I still get the same exception:

<resultMap id="catItemsResults" class="testCat" groupBy="catPK" >
   <result property="catPK" column="cat_pk" javaType="int" 
jdbcType="NUMERIC" nullValue="0"/>
  <result property="catName" column="cat_name" javaType="string" 
jdbcType="CHAR" nullValue="NULL"/>
  <result property="items" javaType="java.util.List" 
resultMap="CatItem.itemsResults" />
</resultMap>

 <resultMap id="itemsResults" class="testItem" >
    <result property="itemPK" column="itm_pk" javaType="int" 
jdbcType="NUMERIC" nullValue="0"/>
    <result property="itemName" column="itm_name" javaType="string" 
jdbcType="CHAR" nullValue="NULL"/>
</resultMap>

<select id="getBatchedItemPromoPrices" resultMap="catItemsResults">
   SELECT cat_pk, itm_pk, cat_name, itm_name FROM testcat LEFT JOIN 
testitem ON cat_pk = itm_cat_fk
</select>

Where is the NullPointerException coming from? I am not very experienced 
with Ibatis and do not know what is going on behind the scenes. This is 
all very frustrating.

Mime
View raw message