I use the following Hibernate query alot when retrieving multiple records by their primary key
Criteria c = session
.createCriteria(Song.class)
.setLockMode(LockMode.NONE)
.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY)
.add(Restrictions.in("recNo", ids));
List<Song> songs = c.list();
The problem is the number of ids can vary from 1 - 50, and every different number of ids requires a different PreparedStatement. That, combined with the fact that any particular prepared statement is tied to a particular database pool connection means that the opportunity to reuse a PreparedStatement is quite low.
Is there way I can rewrite this so that the same statement can be used with different number of in values, I think I read somewhere it could be done by using ANY instead but cannot find the reference.
This is called "in clause parameter padding" and can be activated with a hibernate property:
<property
name="hibernate.query.in_clause_parameter_padding"
value="true"
</property>
Read more about this topic here: https://vladmihalcea.com/improve-statement-caching-efficiency-in-clause-parameter-padding/
With some help I ended up getting a usual SQL connection from Hibernate, and then using standard SQL with ANY instead of IN. As far as I know using ANY means we only need a single prepared statement per connection so is better then using padded IN's. But because just using SQL not much use if you need to modify the data returned
public static List<SongDiff> getReadOnlySongDiffs(List<Integer> ids)
{
Connection connection = null;
try
{
connection = HibernateUtil.getSqlSession();
String SONGDIFFSELECT = "select * from SongDiff where recNo = ANY(?)";
PreparedStatement ps = connection.prepareStatement(SONGDIFFSELECT);
ps.setObject(1, ids.toArray(new Integer[ids.size()]));
ResultSet rs = ps.executeQuery();
List<SongDiff> songDiffs = new ArrayList<>(ids.size());
while(rs.next())
{
SongDiff sd = new SongDiff();
sd.setRecNo(rs.getInt("recNo"));
sd.setDiff(rs.getBytes("diff"));
songDiffs.add(sd);
}
return songDiffs;
}
catch (Exception e)
{
MainWindow.logger.log(Level.SEVERE, "Failed to get SongDiffsFromDb:" + e.getMessage(), e);
throw new RuntimeException(e);
}
finally
{
SessionUtil.close(connection);
}
}
public static Connection getSqlSession() throws SQLException {
if (factory == null || factory.isClosed()) {
createFactory();
}
return ((C3P0ConnectionProvider)factory.getSessionFactoryOptions().getServiceRegistry().getService(C3P0ConnectionProvider.class)).getConnection();
}
If you're still on an old version of Hibernate as suggested in the comments to Simon's answer here, as a workaround, you could use jOOQ's ParsingConnection to transform your SQL by applying the IN list padding feature transparently behind the scenes. You can just wrap your DataSource like this:
// Input DataSource ds1:
DSLContext ctx = DSL.using(ds1, dialect);
ctx.settings().setInListPadding(true);
// Use this DataSource for your code, instead:
DataSource ds2 = ctx.parsingDataSource();
I've written up a blog post to explain this more in detail here.
(Disclaimer: I work for the company behind jOOQ)
Related
I'm executing same command in every 2 seconds. I think following code creates multiple connections:
[System.Web.Services.WebMethod]
public static int getActivity()
{
using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["dbconnection"].ToString()))
{
connection.Open();
using (var cmd = new SqlCommand("SELECT TOP 1 ValueX FROM TABLE WHERE ID= 2 AND EVENTID = 2 ORDER BY DATE DESC", connection))
{
var x = cmd.ExecuteScalar();
int Result;
if (x != null)
{
Result = int.Parse(x.ToString());
Console.WriteLine("USER ACTIVITY : " + Result);
}
else
{
Result = -999;
}
connection.Close();
return Result;
}
}
}
If I call this method several time Does following code make multi connection Or single connection ?
using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["dbconnection"].ToString()))
Can someone explain whether I need to modify this code or Is this good one ?
Thanks.
Since you are using the using statement clause so once you are done with the method the resources are freed and the connection is closed. So everytime when you call the same method a new connection will be made. When you are using the using clause then it is equivalent to the below code:
SqlConnection connection = null;
try
{
connection = new SqlConnection(connectionString);
}
finally
{
if(connection != null)
((IDisposable)connection).Dispose();
}
Also note that you dont need to explicitly call the connection.Close(); in your method as using statement will take care of it.
Your method is fine, you just don't need connection.Close() as described by Rahul. Using statement when dealing with SQL objects is good practice.
What you should keep in mind, is that ADO.NET connection pooling, takes care of handling new objects referring to the same connection string, thus minimizing the time needed to open a connection.
More about connection pooling can be found Here
How can we fetch liferay entities through custom-finder using custom SQL?
Following is my sql query written in default.xml (I have trimmed down the query to the bare minimum so that the logic remains simple. Since it included a few functions and joins we couldn't use DynamicQuery API ):
SELECT
grp.*
FROM
Group_
WHERE
site = 1
AND active_ = 1
AND type_ <> 3
Relevant code in MyCustomGroupFinderImpl.java:
Session session = null;
try {
session = openSession();
// fetches the query string from the default.xml
String sql = CustomSQLUtil.get(FIND_ONLY_ACTIVE_SITES);
SQLQuery sqlQuery = session.createSQLQuery(sql);
sqlQuery.addEntity("Group_", GroupImpl.class);
// sqlQuery.addEntity("Group_", PortalClassLoaderUtil.getClassLoader().loadClass("com.liferay.portal.model.impl.GroupImpl"));
return (List<Group>) QueryUtil.list(sqlQuery, getDialect(), 0, QueryUtil.ALL_POS);
}
catch (Exception e) {
throw new SystemException(e);
}
finally {
closeSession(session);
}
This above code won't work as the GroupImpl class is present in portal-impl.jar and this jar cannot be used in custom portlet.
I also tried using sqlQuery.addEntity("Group_", PortalClassLoaderUtil.getClassLoader().loadClass("com.liferay.portal.model.impl.GroupImpl"))
But this above code throws exception:
com.liferay.portal.kernel.exception.SystemException:
com.liferay.portal.kernel.dao.orm.ORMException:
org.hibernate.MappingException:
Unknown entity: com.liferay.portal.model.impl.GroupImpl
But the same code works for our custom-entity, if we write sqlQuery.addEntity("MyCustomGroup", MyCustomGroupImpl.class);.
Thanks
I found out from the liferay forum thread that instead of session = openSession();
we would need to fetch the session from liferaySessionFactory as follows to make it work:
// fetch liferay's session factory
SessionFactory sessionFactory = (SessionFactory) PortalBeanLocatorUtil.locate("liferaySessionFactory");
Session session = null;
try {
// open session using liferay's session factory
session = sessionFactory.openSession();
// fetches the query string from the default.xml
String sql = CustomSQLUtil.get(FIND_ONLY_ACTIVE_SITES);
SQLQuery sqlQuery = session.createSQLQuery(sql);
// use portal class loader, since this is portal entity
sqlQuery.addEntity("Group_", PortalClassLoaderUtil.getClassLoader().loadClass("com.liferay.portal.model.impl.GroupImpl"));
return (List<Group>) QueryUtil.list(sqlQuery, getDialect(), 0, QueryUtil.ALL_POS);
}
catch (Exception e) {
throw new SystemException(e);
}
finally {
sessionFactory.closeSession(session); // edited as per the comment on this answer
// closeSession(session);
}
Hope this helps somebody on stackoverflow, also I found a nice tutorial regarding custom-sql which also uses the same approach.
We're using NHibernate in a project that gets data out of the database and writes reports to a separate system. In my scenario, a patient will usually, but not always, have a next appointment scheduled when the report gets written. The query below gets the next appointment data, to include in the report.
private NextFollowup GetNextFollowup(int EncounterID)
{
try
{
NextFollowup myNextF = new NextFollowup();
IQuery myNextQ = this.Session.GetNamedQuery("GetNextFollowup").SetInt32("EncounterID", EncounterID);
myNextF = myNextQ.UniqueResult<NextFollowup>();
return myNextF;
}
catch (Exception e)
{
throw e;
}
}
Here's the question:
Usually this works fine, as there is a single result when an appointment is scheduled. However, in the cases where there is no next followup, I get the error that there is no unique result. I don't really want to throw an exception in this case, I want to return the empty object. If I were to get a list instead of a UniqueResult, I'd get an empty list in the situations where there is no next followup. Is there a better way to handle the situation of "when there is a value, there will be only one" than using a list in the HQL query?
This may work:
private NextFollowup GetNextFollowup(int encounterID)
{
IQuery query = this.Session.GetNamedQuery("GetNextFollowup").SetInt32("EncounterID", encounterID);
// nextFollowup will be either the next instance, or null if none exist in the db.
var nextFollowup = query.Enumerable<NextFollowup>().SingleOrDefault();
return nextFollowup;
}
Note: updated naming to follow Microsoft best practices
The try catch is not serving any purpose here except to loose the stack trace if there is an exception so I've removed it.
If you want to return a new NextFollowup if none exist, you can update the query line to:
var nextFollowup = query.Enumerable<NextFollowup>().SingleOrDefault() ?? new NextFollowup();
I'm new to NHibernate and was assigned to a task where I have to change a value of an entity property and then compare if this new value (cached) is different from the actual value stored on the DB. However, every attempt to retrieve this value from the DB resulted in the cached value. As I said, I'm new to NHibernate, maybe this is something easy to do and obviously could be done with plain ADO.NET, but the client demands that we use NHibernate for every access to the DB. In order to make things clearer, those were my "successful" attempts (ie, no errors):
1
DetachedCriteria criteria = DetachedCriteria.For<User>()
.SetProjection(Projections.Distinct(Projections.Property(UserField.JobLoad)))
.Add(Expression.Eq(UserField.Id, userid));
return GetByDetachedCriteria(criteria)[0].Id; //this is the value I want
2
var JobLoadId = DetachedCriteria.For<User>()
.SetProjection(Projections.Distinct(Projections.Property(UserField.JobLoad)))
.Add(Expression.Eq(UserField.Id, userid));
ICriteria criteria = JobLoadId.GetExecutableCriteria(NHibernateSession);
var ids = criteria.List();
return ((JobLoad)ids[0]).Id;
Hope I made myself clear, sometimes is hard to explain a problem when even you don't quite understand the underlying framework.
Edit: Of course, this is a method body.
Edit 2: I found out that it doesn't work properly for the method call is inside a transaction context. If I remove the transaction, it works fine, but I need it to be in this context.
I do that opening a new stateless session for geting the actual object in the database:
User databaseuser;
using (IStatelessSession session = SessionFactory.OpenStatelessSession())
{
databaseuser = db.get<User>("id");
}
//do your checks
Within a session, NHibernate will return the same object from its Level-1 Cache (aka Identity Map). If you need to see the current value in the database, you can open a new session and load the object in that session.
I would do it like this:
public class MyObject : Entity
{
private readonly string myField;
public string MyProperty
{
get { return myField; }
set
{
if (value != myField)
{
myField = value;
DoWhateverYouNeedToDoWhenItIsChanged();
}
}
}
}
googles nhforge
http://nhibernate.info/doc/howto/various/finding-dirty-properties-in-nhibernate.html
This may be able to help you.
I was wondering if there is any way to intercept and modify the sql generated from linq to Sql before the query is sent off?
Basically, we have a record security layer, that given a query like 'select * from records' it will modify the query to be something like 'select * from records WHERE [somesecurityfilter]'
I am trying to find the best way to intercept and modify the sql before its executed by the linq to sql provider.
Ok, first to directly answer your question (but read on for words of caution ;)), there is a way, albeit a finicky one, to do what you want.
// IQueryable<Customer> L2S query definition, db is DataContext (AdventureWorks)
var cs = from c in db.Customers
select c;
// extract command and append your stuff
DbCommand dbc = db.GetCommand(cs);
dbc.CommandText += " WHERE MiddleName = 'M.'";
// modify command and execute letting data context map it to IEnumerable<T>
var result = db.ExecuteQuery<Customer>(dbc.CommandText, new object[] { });
Now, the caveats.
You have to know which query is generated so you would know how to modify it, this prolongs development.
It falls out of L2S framework and thus creates a possible gaping hole for sustainable development, if anyone modifies a Linq it will hurt.
If your Linq causes parameters (has a where or other extension causing a WHERE section to appear with constants) it complicates things, you'll have to extract and pass those parameters to ExecuteQuery
All in all, possible but very troublesome. That being said you should consider using .Where() extension as Yaakov suggested. If you want to centrally controll security on object level using this approach you can create an extension to handle it for you
static class MySecurityExtensions
{
public static IQueryable<Customer> ApplySecurity(this IQueryable<Customer> source)
{
return source.Where(x => x.MiddleName == "M.");
}
}
//...
// now apply it to any Customer query
var cs = (from c in db.Customers select c).ApplySecurity();
so if you modify ApplySecurity it will automatically be applied to all linq queries on Customer object.
If you want to intercept the SQL generated by L2S and fiddle with that, your best option is to create a wrapper classes for SqlConnection, SqlCommand, DbProviderFactory etc. Give a wrapped instance of SqlConnection to the L2S datacontext constructor overload that takes a db connection. In the wrapped connection you can replace the DbProviderFactory with your own custom DbProviderFactory-derived class that returns wrapped versions of SqlCommand etc.
E.g.:
//sample wrapped SqlConnection:
public class MySqlConnectionWrapper : SqlConnection
{
private SqlConnecction _sqlConn = null;
public MySqlConnectionWrapper(string connectString)
{
_sqlConn = new SqlConnection(connectString);
}
public override void Open()
{
_sqlConn.Open();
}
//TODO: override everything else and pass on to _sqlConn...
protected override DbProviderFactory DbProviderFactory
{
//todo: return wrapped provider factory...
}
}
When using:
using (SomeDataContext dc = new SomeDataContext(new MySqlConnectionWrapper("connect strng"))
{
var q = from x in dc.SomeTable select x;
//...etc...
}
That said, do you really want to go down that road? You'll need to be able to parse the SQL statements and queries generated by L2S in order to modify them properly. If you can instead modify the linq queries to append whatever you want to add to them, that is probably a better alternative.
Remember that Linq queries are composable, so you can add 'extras' in a separate method if you have something that you want to add to many queries.
first thing come to my mind is to modify the query and return the result in Non-LINQ format
//Get linq-query as datatable-schema
public DataTable ToDataTable(System.Data.Linq.DataContext ctx, object query)
{
if (query == null)
{
throw new ArgumentNullException("query");
}
IDbCommand cmd = ctx.GetCommand((IQueryable)query);
System.Data.SqlClient.SqlDataAdapter adapter = new System.Data.SqlClient.SqlDataAdapter();
adapter.SelectCommand = (System.Data.SqlClient.SqlCommand)cmd;
DataTable dt = new DataTable("sd");
try
{
cmd.Connection.Open();
adapter.FillSchema(dt, SchemaType.Source);
adapter.Fill(dt);
}
finally
{
cmd.Connection.Close();
}
return dt;
}
try to add your condition to the selectCommand and see if it helps.
Try setting up a view in the DB that applies the security filter to the records as needed, and then when retrieving records through L2S. This will ensure that the records that you need will not be returned.
Alternatively, add a .Where() to the query before it is submitted that will apply the security filter. This will allow you to apply the filter programmatically (in case it needs to change based on the scenario).