Sounds like as of 2.0.9 there is a way to do what Marty is asking:
# Solution for N+1 selects for 1:M and M:N. Version 2.0 was always designed for this, I just didn't have a chance to implement it, until now. It's made possible by two small additions to the mappings
* <resultMap...groupBy="prop1,prop2">
* <result...resultMap="subResultMapForCollectionItems">Is there any documentation or examples about the "groupBy" property?
James, Steven wrote:
hi Marty,
Your query is not in the right context and is doing what you ask. You are doing a join and as you have to records in the sub table that meet the requirments of your join ie WHERE A.ALERT_ID=AC.ALERT_ID then two rows are returned. This is only good for N:1 situations.
You have a N:M situation. Easiest solution do a follow up query see page 26 0f 53 in ibatis-sqlmap.pdf file. ie.
<result property="criteriaList" select="getMyAlertCriteia"/>
This will envolve a second hit on your database.
other option use a lazy loading technique to only get the data when you need it.
Good luck steve..
-----Original Message-----
From: Marty Tomasi [mailto:[EMAIL PROTECTED]
Sent: Thu 3/10/2005 1:20 AM
To: [email protected]
Subject: Questions on N+1 and ParameterMap
Hi,
First off, excellent work to date on iBATIS. It's been a real treat to work with so far. I could go on, but....
I have some questions. Note that I am using the latest 2.0.9B code when running this code.
Given two tables with the following:
Table: ALERTS +----------+----------------+------------+--------------+
| alert_id | event_name | subscriber | active_state |
+----------+----------------+------------+--------------+
| 1001 | ContentAdded | demouser | 1 |
| 1002 | ContentUpdated | demouser | 1 |
+----------+----------------+------------+--------------+
Table: ALERT_CRITERIA +----------+-----------+----------+---------------+------+ | alert_id | attribute | operator | value | type | +----------+-----------+----------+---------------+------+ | 1001 | Document | 4 | D003EFF4C0099 | 12 | | 1002 | Document | 4 | C900EF808099C | 12 | | 1002 | Status | 4 | 200 | 8 | +----------+-----------+----------+---------------+------+
There are two Java beans, Alert and AlertCriteria with the appropriate member fields. Pretty standard stuff, other than the fact that Alert also has a List of AlertCriteria objects; hence the 1:N relationship.
Here is the SQL Mapping:
<sqlMap namespace="Alerts">
<typeAlias alias="alert" type="com.myorg.alerts.Alert"/> <typeAlias alias="alertCondition" type="com.myorg.alerts.AlertCriteria"/> <typeAlias alias="alertParam" type="com.myorg.alerts.AlertParameterMap"/>
<resultMap id="criteriaResult" class="alertCriteria" groupBy="alertId">
<result property="alertId" column="ALERT_ID"/>
<result property="attribute" column="ATTRIBUTE"/>
<result property="operator" column="OPERATOR"/>
<result property="value" column="VALUE"/>
<result property="type" column="TYPE"/>
</resultMap>
<resultMap id="findAlertsResult" class="alert">
<result property="id" column="ALERT_ID"/>
<result property="eventName" column="EVENT_NAME"/>
<result property="subscriber" column="SUBSCRIBER"/>
<result property="active" column="ACTIVE_STATE"/>
<result property="criteriaList" resultMap="Alerts.criteriaResult"/>
</resultMap>
<parameterMap id="alertParamMap" class="alertParam">
<parameter property="eventName"/>
<parameter property="attributes"/>
</parameterMap>
<select id="findActiveAlerts" parameterMap="alertParamMap" resultMap="Alerts.findAlertsResult">
SELECT A.*, AC.* FROM ALERTS A, ALERT_CRITERIA AC
WHERE A.ALERT_ID=AC.ALERT_ID
AND A.EVENT_NAME=#eventName#
AND A.ACTIVE_STATE=1
<iterate prepend="AND" property="attributes" open="(" close=")" conjunction="OR">
AC.ATTRIBUTE=#attributes[]#
</iterate>
</select>
. . .
</sqlMap>
The AlertParameterMap is a parameter mapping used so that 1 to n "attributes" can be passed in to the "findActiveAlerts" query. Its attributes property is a List, which is then used in the <iterate> element of the query. (Nice feature, btw.)
Here's what happens. Consider a query where the AlertParameterMap contains a single attribute (attributes.size() = 1) and the eventName="ContentAdded". When I execute the queryForList() with that parameter map, I get back a single Alert. Makes sense because the SQL returns: +----------+--------------+------------+--------------+----------+-----------+----------+---------------+------+ | ALERT_ID | EVENT_NAME | SUBSCRIBER | ACTIVE_STATE | ALERT_ID | ATTRIBUTE | OPERATOR | VALUE | TYPE | +----------+--------------+------------+--------------+----------+-----------+----------+---------------+------+ | 1001 | ContentAdded | demouser | 1 | 1001 | Document | 4 | D003EFF4C0099 | 12 | +----------+--------------+------------+--------------+----------+-----------+----------+---------------+------+
The List returned by queryForList() contains a single Alert object, as expected. The List of AlertCriteria on the Alert object has a single object as well.
However, when I try a query where the AlertParameterMap contains multiple attributes (attributes.size() > 1) using, for example, eventName="ContentUpdated", the SQL returns: +----------+----------------+------------+--------------+----------+-----------+----------+---------------+------+ | ALERT_ID | EVENT_NAME | SUBSCRIBER | ACTIVE_STATE | ALERT_ID | ATTRIBUTE | OPERATOR | VALUE | TYPE | +----------+----------------+------------+--------------+----------+-----------+----------+---------------+------+ | 1002 | ContentUpdated | demouser | 1 | 1002 | Document | 4 | C900EF808099C | 12 | | 1002 | ContentUpdated | demouser | 1 | 1002 | Status | 4 | 200 | 8 | +----------+----------------+------------+--------------+----------+-----------+----------+---------------+------+
The List returned by queryForList() contains two (2) Alert objects instead of the expected one (based on the id 1002 in this example). Further, the first Alert object has a List of AlertCriteria with a single AlertCriteria (where attribute="Document", etc.). The second Alert object has a null value for the AlertCriteria.
The expected result is a single Alert object whose criteriaList is size()=2 with both criteria (attribute="Document" and attribute="Status") present.
Any thoughts or suggestions as to what is incorrect? Is the parameter map not working as I expect? Are my expectations way off base?
Any insight would be greatly appreciated.
Thanks,
Marty
------------------- Marty Tomasi [EMAIL PROTECTED]
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