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.
