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Entity Framework Self-Referencial Many-To-Many with Payload ( Bill of Materials BOM )

Answer 1

+1 A:

So I ended up with a surprisingly graceful solution.

CREATE TABLE Resource
(
ID INT NOT NULL,
Type VARCHAR(25) NOT NULL
)

ALTER TABLE Resource
ADD CONSTRAINT PK_Resource PRIMARY KEY (ID)

CREATE TABLE ResourceHierarchy
(
Ancestor_ID INT NOT NULL,
Descendant_ID INT NOT NULL,
Required INT NOT NULL DEFAULT 1
)

ALTER TABLE ResourceHierarchy
ADD CONSTRAINT PK_ResourceHierarchy PRIMARY KEY (Ancestor_ID, Descendant_ID)
ALTER TABLE ResourceHierarchy
ADD CONSTRAINT FK_Ancestors FOREIGN KEY (Ancestor_ID) REFERENCES Resource (ID)
ALTER TABLE ResourceHierarchy
ADD CONSTRAINT FK_Descendants FOREIGN KEY (Descendant_ID) REFERENCES Resource (ID)

When the EDMX was generated I renamed the Resource Entity navigation properties from ResourceHierarchy to DescendantRelationships and ResourceHierarchy1 to AncestorRelationships. I then renamed the ResourceHierarchy Entity navigation properties from Resource to Descendant and Resource1 to Ancestor.

Whereas before I could write code like this:

Resource resource = new Resource();
resource.Descendants.Add(new Resource());
foreach (Resource descendant in resource.descendants)
{
descendant.Type = "Brawr";
List<Resource> ancestors = descendant.Ancestors.ToList();
}

Of course this approach did not allow me to access the Required property.

Now I must do the following:

Resource ancestor = new Resource();
Resource descendant = new Resource();

ResourceHierarchy rh = new ResourceHierarchy { Ancestor = ancestor, Descendant = descendant, Required = 1 };

ancestor.DescendantRelationships.Add(rh);

But check it out I can now get to the Required property like so:

int req = ancestor.DescendantRelationships.First().Required;

One might rename the Required field to RequiredDescendants since Descendants don't need a required amount of Ancestors, only Ancestors need to specify how many Descendants are required.

So it's a hop, but a graceful one.

Please let me know your thoughts, especially if I've overlooked a gotcha or something.

aframeb 2010-10-13 20:56:36

Answer 2

A:

Something to watch out for...

When we want to add a descendant to a resource we need to remember that DescendantRelationships gives us the hierarchy where the referenced resource is acting as descendants to other resources.

So in order to add a descendant to a resource we must do the following:

Resource resource = new Resource { Type = "WidgetA" };
Resource descendant = new Resource { Type = "Screw" };
resource.AncestorRelationships.Add(new ResourceHierarchy { Descendant = descendant, Required = 1 };

Of course this all depends on how you name your navigation properties, I'm just saying be careful. AncestorRelationships would be the go to navigation property in order to add descendants and vice versa. A better thing to do might be to rename AncestorRelationships to AncestorRoles and DescendantRelationships to DescendantRoles.

AncestorRoles would translate to ResourceHierarchiesWhereCurrentResourceIsAnAncestor. DescendantRoles would translate to ResourceHierarchiesWhereCurrentResourceIsADescendant.

So we could do:

// print descendant types
foreach (ResourceHierarchy rh in resource.AncestorRoles)
{
Console.WriteLine(rh.Descendant.ResourceType.Type);
}

Sorry to change up the nomenclature so much but I think it helps understand what's going on.

aframeb 2010-10-14 14:50:51

Answer 3

A:

The MSDN Libary link : http://msdn.microsoft.com/en-us/library/ms742451.aspx is titled PropertyPath XAML Syntax and has a section titled Source Traversal (Binding to Hierarchies of Collections)

This is the HierarchicalDataTemplate I want to use:

<HierarchicalDataTemplate DataType="{x:Type Inventory:Resource}" ItemsSource="{Binding Path=AncestorRoles/Descendant}">
<CustomControls:ResourceTreeItem Type="{Binding ResourceType.Type}"/>
</HierarchicalDataTemplate>

Only the first Resource is displayed. After the following code runs the TreeView shows one ResourceTreeItem in the TreeView.

ObservableCollection<Resource> Resources = new ObservableCollection<Resource>
Resources.Add(new Resource { ResourceType.Type = "WidgetA" });
MyTreeView.ItemsSource = Resources;

So that works. However when I run the following code the TreeView is not updated.

Resource resource = MyTreeView.Items[0] as Resource;
resource.AncestorRoles.Add( new ResourceHierarchy { Descendant = new Resource { ResourceType = "Screw" }, Required = 1 } )

Even if I get the CollectionViewSource of the TreeView.ItemsSource and call Refresh() it doesn't show up. I triple checked the relationships and it's all there.

I think it's a bug with the PropertyPath Traversal syntax.

The solution was to add a TreeParent property to the Resource partial class declaration and utilize 3 ValueConverters which is a long story but it's because the datacontext naturally alternates from a Resource to a ResourceHierarchy. The RequiredConverter is the one that checks the TreeParent and finds the Required property Payload.

class ValidatorConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            Resource resource = value as Resource;
            ResourceHierarchy rh = value as ResourceHierarchy;
            if (resource != null)
            {
                value = resource;
            }
            else if (rh != null)
            {
                value = rh.Descendant;
            }

            return value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

    class ResourceConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            Resource resource = value as Resource;
            ResourceHierarchy hierarchy = value as ResourceHierarchy;

            if (resource != null)
            {
                if (resource.AncestorRoles.Count > 0)
                {
                    value = resource.AncestorRoles;
                }
                else
                {
                    value = resource;
                }
            }
            else if (hierarchy != null)
            {
                value = hierarchy.Descendant.AncestorRoles;
            }

            return value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

    class RequiredConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            Resource resource = (Resource)value;
            Resource parent = ((Resource)value).TreeParent as Resource;
            if (parent != null)
            {
                value = parent.AncestorRoles.Where(p => p.Descendant == resource).First().Required;
            }
            else
            {
                value = 0;
            }

            return value;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

And here is the final HierarchicalDataTemplate:

<HierarchicalDataTemplate DataType="{x:Type Inventory:Resource}" ItemsSource="{Binding Path=., Converter={StaticResource resourceconv}}">
<StackPanel DataContext="{Binding Path=., Converter={StaticResource validatorconv}}">
<CustomControls:ResourceTreeItem Required="{Binding Path=., Converter={StaticResource requiredconv}}" Free="{Binding Free}" OnHand="{Binding OnHand, Mode=TwoWay}" Type="{Binding ResourceType.Type}"/>
</StackPanel>
</HierarchicalDataTemplate>

The StackPanel only serves to add another DataContext layer. I left in the Free, OnHand and Type properties so you could see that 3 properties are receiving their binding from the StackPanels DataContext and the Required property is doing it's thing like a mad man.

So the moral is if you need a Payload maybe the EF isn't for you.

aframeb 2010-10-14 20:55:01

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Entity Framework Self-Referencial Many-To-Many with Payload ( Bill of Materials BOM )

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