Question

I was doing a simple 2 level caching experiment with Stored Procedures and am receiving a table or view does not exist Oracle error.

The cache is retrieving my DTO object and trying to make a SQL statement to the database. I’m guessing it is some configuration error.

Here’s the app.config

<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
<session-factory name="NHibernate.Test">
  <property name="connection.driver_class">NHibernate.Driver.OracleDataClientDriver</property>
  <property name="show_sql">true</property>
  <property name="dialect">NHibernate.Dialect.Oracle10gDialect</property>
  <property name="query.substitutions">true 1, false 0, yes 'Y', no 'N'</property>
  <property name="cache.use_query_cache">true</property>
  <property name="cache.use_second_level_cache">true</property>
  <property name="cache.provider_class">NHibernate.Caches.SysCache.SysCacheProvider, NHibernate.Caches.SysCache</property>
</session-factory>
</hibernate-configuration>

And here’s the code to test:
[TestMethod]
public void GetNomHeaderInfo_TestingCache_BPNomHeaderShouldBeCached()
{
//Arrange
DateTime StartTime;
DateTime EndTime;
TimeSpan FirstTry;
TimeSpan SecondTry;

    //Act
    using (var session = factory.OpenSession())
    {
        var query = session.GetNamedQuery("GetMyDTO");
        query.SetInt32("id", 1);
        query.SetCacheRegion("Id");
        query.SetCacheMode(CacheMode.Normal);
        query.SetCacheable(true);
        StartTime = DateTime.Now;
        myDTO DTO = query.UniqueResult<myDTO>();
        EndTime = DateTime.Now;
        FirstTry = EndTime - StartTime;
    }

    using (var session = factory.OpenSession())
    {
        var query = session.GetNamedQuery("GetMyDTO");
        query.SetInt32("id", 1);
        query.SetCacheRegion("Id");
        query.SetCacheMode(CacheMode.Normal);
        query.SetCacheable(true);
        StartTime = DateTime.Now;
        myDTO DTO = query.UniqueResult<myDTO>();
        EndTime = DateTime.Now;
        SecondTry = EndTime - StartTime;
    }

    //Test
    Assert.IsTrue(SecondTry < FirstTry);
}

I then error out when I do the second query.UniqueResult(); The error message is:

SELECT blah blah_.blahblah, etc FROM MyDTO SomeAlias_ WHERE SomeAlias_.id=:p0

But there’s no myDTO table or view. I don’t know why NHibernate thinks to pull from the cache myDTO and then tries to create a SQL statement.

Here’s the trace:

NHibernate.Cache.StandardQueryCache: DEBUG checking cached query results in region: 'Id'; sql: { call SomePackage.MyProc(?) }; parameters: []; named parameters: {'id'='1'}
NHibernate.Cache.StandardQueryCache: DEBUG checking cached query results in region: 'Id'; sql: { call SomePackage.MyProc(?) }; parameters: []; named parameters: {'id'='1'}
NHibernate.Caches.SysCache.SysCache: DEBUG Fetching object 'NHibernate-Cache:nomId:sql: { call SomePackage.MyProc(?) }; parameters: []; named parameters: {'id'='1'}@601355831' from the cache.
NHibernate.Caches.SysCache.SysCache: DEBUG Fetching object 'NHibernate-Cache:nomId:sql: { call SomePackage.MyProc(?) }; parameters: []; named parameters: {'id'='1'}@601355831' from the cache.
NHibernate.Cache.StandardQueryCache: DEBUG Checking query spaces for up-to-dateness [MyDTO]
NHibernate.Cache.StandardQueryCache: DEBUG Checking query spaces for up-to-dateness [MyDTO]
NHibernate.Caches.SysCache.SysCache: DEBUG Fetching object 'NHibernate-Cache:UpdateTimestampsCache:MyDTO@1270222867' from the cache.
NHibernate.Caches.SysCache.SysCache: DEBUG Fetching object 'NHibernate-Cache:UpdateTimestampsCache:MyDTO@1270222867' from the cache.
NHibernate.Cache.StandardQueryCache: DEBUG returning cached query results for: sql: { call SomePackage.MyProc(?) }; parameters: []; named parameters: {'id'='1'}
NHibernate.Cache.StandardQueryCache: DEBUG returning cached query results for: sql: { call SomePackage.MyProc(?) }; parameters: []; named parameters: {'id'='1'}
NHibernate.Event.Default.DefaultLoadEventListener: DEBUG loading entity: [MyAssembly.MyDTO#1]
NHibernate.Event.Default.DefaultLoadEventListener: DEBUG loading entity: [MyAssembly.MyDTO#1]
NHibernate.Event.Default.DefaultLoadEventListener: DEBUG attempting to resolve: [MyAssembly.MyDTO#1]
NHibernate.Event.Default.DefaultLoadEventListener: DEBUG attempting to resolve: [MyAssembly.MyDTO#1]
NHibernate.Event.Default.DefaultLoadEventListener: DEBUG object not resolved in any cache: [MyAssembly.MyDTO#1]
NHibernate.Event.Default.DefaultLoadEventListener: DEBUG object not resolved in any cache: [MyAssembly.MyDTO#1]
NHibernate.Persister.Entity.AbstractEntityPersister: DEBUG Fetching entity: [MyAssembly.MyDTO#1]
NHibernate.Persister.Entity.AbstractEntityPersister: DEBUG Fetching entity: [MyAssembly.MyDTO#1]
NHibernate.Loader.Loader: DEBUG loading entity: [MyAssembly.MyDTO#1]
NHibernate.Loader.Loader: DEBUG loading entity: [MyAssembly.MyDTO#1]
NHibernate.AdoNet.AbstractBatcher: DEBUG Opened new IDbCommand, open IDbCommands: 1
NHibernate.AdoNet.AbstractBatcher: DEBUG Opened new IDbCommand, open IDbCommands: 1
NHibernate.AdoNet.AbstractBatcher: DEBUG Building an IDbCommand object for the SqlString: SELECT blah blah_.blahblah, etc FROM MyDTO SomeAlias_ WHERE SomeAlias_.id=:p0

Anyone know what I’m doing wrong here?

Thanks, Bill N

Answer 1

I can’t see your mapping, but here’s an explanation.

• You are caching your query results, but not your entity (those are separate caches)
• Caching a query’s results just stores the IDs; if you are not caching your entities too, a query is issued to load each returned entity (this is usually bad)
• The default table name for the MyDTO class is MyDTO, so that’s where it’s looking
• This looks like a Query by ID, for which you shouldn’t be using a loose named query, but a proper loader (see 17.4. Custom SQL for loading).

Once you set up the loader and entity caching, you’ll just be able to retrieve your objects using just session.Get<MyDTO>(id), which will use the second level cache, as long as you do all of your work inside transactions, which is a recommended practice.