If you want to bind a big Hibernate query result to a DataGridView in winform, you probably would like to use the SetFirstResult-SetMaxResults features avaiable in IQuery or ICriteria to achieve some kind of "paging". In winform you can chieve this by using virtual mode, but in this case you cannot deal with a DataBound grid, and the presentation code is generally worst. Another problem with paging strategy is sorting the results set. To solve this I created a very simple (abstract ) class that act as a sortable DataSource and transparently drives hibernate to fetch the records in pages. See below the class diagram:
As you can see, to use the class you must derive one , that must implement:
- GetTotalCount : returns the whole recordset count based on the objects you need to show
- GetFillCriteria: returns a ICriteria based on your requirement.
following a sample implementation class:
12 public class JobPagedDataSource:NHibernatePagedDataSource
13 {
14
15 public JobPagedDataSource(int pageSize,ISessionFactory factory)
16 :base(pageSize,factory)
17 {
18
19 }
20 protected override int GetTotalCount(ISessionFactory factory)
21 {
22 ISession session = Factory.SessionFactory.OpenSession();
23 IEnumerable cntEn = session.CreateQuery("select count(*) From ....").Enumerable();
24 IEnumerator en = cntEn.GetEnumerator();
25 en.MoveNext();
26 session.Close();
27 return (int)(long)en.Current;
28 }
29
30 protected override ICriteria GetFillCriteria(ISession session
31 , PropertyDescriptor sortProperty
32 , ListSortDirection direction)
33 {
34 ICriteria crit = session.CreateCriteria(typeof(.....));
35 if (sortProperty != null)
36 {
37 if( direction == ListSortDirection.Ascending )
38 crit.AddOrder( Order.Asc(sortProperty.Name));
39 else
40 crit.AddOrder( Order.Desc(sortProperty.Name));
41 }
42 return crit;
43 }
44 }
If your object does not exactly fit what you need to present to the user, you will probably override the function ApplyObjectDecorator, taking as input the original "hibernated" object and returning your presenter. In this case you would probably do more check in the GetFillCriteria, to properly set the filtering properties.
So, how to attach this to a DataGridView ? Simply do something like:
MyDataGridView.DataSource = new MyImplNHibernatePagedDataSource(50,MySessionFactory);
and the grid is ready to presents and sort, using a Page Size of 50 objects. For lazy objects you can experience some problem, just because the session will be closed before the datagrid use the objects, and you will have some proxy exception. There is no way out to deal with this, use eager fetch, or avoid to display the lazy columns.
nhibernatepageddatasource.cs (6,34 kb)
nhibernatepageddatasource.zip (1,49 kb)