Hi, this problem extends past just NHibernate, its a general problem with databinding, but since it will come up constantly with NHibernate, I am wondering if anyone here knows how to deal with this.


How do you databind a DataGridViewComboBoxColumn?


For example, let's say you had a DataGridView and set its datasource as such:

dgv.DataSource = dataAcces.GetAll<Person>();

And let's say the "Person" class has a reference to a "MapLocation" as such:

public class Person
{
public virtual int Id { get; private set; }
public virtual string Name { get; set; }
public virtual MapLocation { get; set; }
}

And MapLocation is defined as:

public class MapLocation
{
public virtual int Id { get; private set; }
public virtual string MapName { get; set; }
}

Now suppose we add a DataGridViewComboBoxColumn to our "dgv" DataGridView:

dgv.Columns.Add(
new DataGridViewComboBoxColumn
{
HeaderText = "Map",
DataPropertyName = "MapLocation",
DataSource = dataAcces.GetAll<MapLocation>(),
DisplayMember = "MapLocationName",
//ValueMember = "MapLocation", // WHAT GOES HERE
DisplayStyleForCurrentCellOnly = true,
FillWeight = 1
});


How do you set up this databinding??

Ideally I would set up the comboboxcolumn with:

DataPropertyName = "MapLocation.Id"
DisplayMember = "MapLocationName"
ValueMember = "Id"

Except that "MapLocation.Id" is not possible.

So, how is this databinding accomplished? Thanks

I did something similar here:



The DataGridViewColumn was set up like this:


locationBindingSource is a BindingSource using the Location Class as DataSource.

So if you change the value in the ComboBox in the Grid the Property looks up the Location in the Dictionary and passes it back.

I did something similar here:



The DataGridViewColumn was set up like this:


locationBindingSource is a BindingSource using the Location Class as DataSource.

So if you change the value in the ComboBox in the Grid the Property looks up the Location in the Dictionary and passes it back.

I thought the whole point of NHibernate (and Hibernate in general) was that you could map your database table models to POCOs (plain old C# objects).

No offense, but what you've written hardly looks like a plain old C# object anymore. It has a custom querying language embedded in it for chrissakes.

Well... mapping an Object into a DataGridView column is simply not possible. So you have to tell the DataGridView which property to show and how they are connected.
That's nothing else for any other Lookup functionality. If you connect the DataGridView with a TableAdapter the MapLocation in your Table would be a int (or something similar) and not a complex class.
Maybe there's a more comfortable way to do such a mapping. I'm neither a CSharp Guru nor am I a NHibernate Guru.

I am neither as well :)

What I mean is, if NHibernate can't handle a fundamental thing like WinForms databinding in an elegant manner, maybe NHibernate sucks for a WinForms application. In fact it seems like that is the case, unless someone knows something I don't about how to do this easily.

Try DisplayMember = "Name" and no ValueMember, since your combobox datasource contains MAPLocation objects.

Did not work for me, though it was a really nice idea.

I meant DisplayMember="MapName", but you probably tried that. Have you implemented GetHashCode() and Equals() on MapLocation ? Since you most likely have different instances of MapLocation in the data-bound item and the combobox datasource, you have to make sure that the objects are considered equal when they have the same id !

Have a look here if you need more information:

http://nhforge.org/blogs/nhibernate/archive/2008/09/06/identity-field-equality-and-hash-code.aspx

You can start with implementing the standard overrides and set breakpoints and check what's happending during databinding. Additionally you can implement Format and Parse events on the grid and check the object types you're dealing with. It's always a hassle ...

That was my second thought, too. I tried to override the GetHashCode and Equals function, but that didn't help either.
But I don't think this is a NHibernate specific problem as it would happen for every Object containing another Object.
I've searched the Internet for binding objects to a GridViewComboBoxColumn, but didn't find any nice way to do it. I'll have a look at it, if I'm back at work :)

I'm coming to the conclusion that you simply [i][b]can not databind effectively using ANY form of domain-driven design[/b][/i]!

It's simply not possible.

It's true that this is more of a fault of how databinding is handled in WinForms than an indictment against DDD in general.

However, the fact remains that these two things do not, in their current form, coexist.[/i]

if you need that very urgently there are several implementations of a DataGridViewComboBoxCell supporting Object binding in the Internet.