Hi All,
I have basic performance question about NHibernate.
Suppose two simple test tables:
CREATE TABLE "TestMaster"
(
"IdM" serial NOT NULL,
"Text" character varying(20),
CONSTRAINT "PK_TestMaster" PRIMARY KEY ("IdM" )
);
CREATE TABLE "TestDetail"
(
"IdD" serial NOT NULL,
"IdM" integer NOT NULL,
"Text" character varying(30),
CONSTRAINT "PK_TestDetail" PRIMARY KEY ("IdD" ),
CONSTRAINT "FK_TestDetail_TestMaster" FOREIGN KEY ("IdM")
REFERENCES "TestMaster" ("IdM") MATCH SIMPLE
ON UPDATE CASCADE ON DELETE RESTRICT
);
for these two tables I have these two mappings:
<class name="TestMaster" schema="public" table="`TestMaster`" lazy="true">
<id name="IdM" column="`IdM`" />
<property name="Text" column="`Text`" />
<bag name="ListTestDetail" schema="public" table="`TestDetail`"
inverse="true" cascade="all-delete-orphan">
<key column="`IdM`" />
<one-to-many class="TestDetail" />
</bag>
</class>
<class name="TestDetail" schema="public" table="`TestDetail`" lazy="true">
<id name="IdD" column="`IdD`" />
<property name="Text" column="`Text`" />
<many-to-one name="LinkTestMaster" class="TestMaster" column="`IdM`" />
</class>
and two classes:
public class TestMaster
{
public virtual int IdM { get; set; }
public virtual string Text { get; set; }
public virtual IList<ORM.TestDetail> ListTestDetail { get; set; }
}
public class TestDetail
{
public virtual int IdD { get; set; }
public virtual String Text { get; set; }
public virtual TestMaster LinkTestMaster { get; set; }
}
Suppose there are 1000 rows in the TestMaser table. If I run this code:
using (ISession ormSession = OrmSessionFactory.OpenSession()) {
IList<ORM.TestMaster> lm = ormSession.CreateQuery("from
TestMaster").List<ORM.TestMaster>();
int cnt = 0;
foreach (ORM.TestMaster tm in lm) {
cnt += tm.ListTestDetail.Count;
}
}
then I see 1+1000 selects in the output window (I know why - first select
for the TestMaster table and 1000 selects for TestDetail where IdM=... when
I evaluate the detail records) and the performance is very low. I tried to
change the test code to:
using (ISession ormSession = OrmSessionFactory.OpenSession()) {
IList<ORM.TestMaster> lm = ormSession.CreateQuery("from
TestMaster").List<ORM.TestMaster>();
*IList<ORM.TestDetail> ld = ormSession.CreateQuery("from
TestDetail").List<ORM.TestDetail>();*
int cnt = 0;
foreach (ORM.TestMaster tm in lm) {
cnt += tm.ListTestDetail.Count;
}
}
in order to read all TestDetail records into the NHibernate's inner memory
(and let him read TestDetail records from inner memory instead of database)
but no success.
Is there some way I can convert scenario 1+1000 to 1+1 (1st select for
TestMaster, 2nd select for TestDetail)?
I'm sure this behavior comes from my misunderstandig and low NH knowledge,
but I was not able to find the solution in this group.
Thank you
IvoD
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