Odd Entity Framework Core v2.2.6 NavigationEntry::Load behavior

[Mad Hat]

I have a database created using a code first approach using EF Core v2.2.6. The database is accessed by users via a desktop app and from within a COM registered SolidWorks Add-In(hence the need to use EF Core v2.2.6).

Everything works as expected when reading and writing from the desktop app, but when NavigationEntry::Load is called from within the add-in, I get this exception

Exception thrown: 'System.InvalidOperationException' in Microsoft.EntityFrameworkCore.dll
The type of navigation property 'Projects' on the entity type 'Customer' is 'IReadOnlyCollection<Project>' for which it was not possible to create a concrete instance. Either initialize the property before use, add a public parameterless constructor to the type, or use a type which can be assigned a HashSet<> or List<>.

This is the configuration class for the Customer class that is added to the ModelBuilder

Public Class CustomerConfig 
	Implements IEntityTypeConfiguration(Of Customer)

	Public Sub Configure(builder As EntityTypeBuilder(Of Customer)) Implements IEntityTypeConfiguration(Of Customer).Configure
		
		builder.Metadata.FindNavigation(NameOf(Customer.Projects)) _ 
			.SetPropertyAccessMode(PropertyAccessMode.Field)

	End Sub

End Class

The Customer class

Public NotInheritable Class Customer
  Private _Projects As HashSet(Of Project)

  Public ReadOnly Property Projects As IReadOnlyCollection(Of Project)
	Get
		Return _Projects
	End Get
  End Property

End Class

How the NavigationEntry is loaded

Sub LoadProjectCustomer(project as Project, context as DbContext)

	Dim custNavEnt = context.Entry(project).Navigations _ 
	.First(Function(e) e.Metadata.Name = "Customer")
	
	custNavEnt.Load()'<- Exception thrown here when called from COM object

End Sub

I am assuming that the issues is because it is being called from within a COM object. I could change how all the classes expose their navigation collections but I would rather not open up those collections even just within the namespace. I do not like to construct the collections in the Db entity class's constructor that is called by the Model Builder because having the navigation collections null is a good way to indicate if the entity has not had it's properties loaded and that it is not just a new entity with an empty collection.

[Peter Swinkels]

I have a database created using a code first approach using EF Core v2.2.6. The database is accessed by users via a desktop app and from within a COM registered SolidWorks Add-In(hence the need to use EF Core v2.2.6).

Everything works as expected when reading and writing from the desktop app, but when NavigationEntry::Load is called from within the add-in, I get this exception

Exception thrown: 'System.InvalidOperationException' in Microsoft.EntityFrameworkCore.dll
The type of navigation property 'Projects' on the entity type 'Customer' is 'IReadOnlyCollection<Project>' for which it was not possible to create a concrete instance. Either initialize the property before use, add a public parameterless constructor to the type, or use a type which can be assigned a HashSet<> or List<>.

This is the configuration class for the Customer class that is added to the ModelBuilder

Public Class CustomerConfig 
	Implements IEntityTypeConfiguration(Of Customer)

	Public Sub Configure(builder As EntityTypeBuilder(Of Customer)) Implements IEntityTypeConfiguration(Of Customer).Configure
		
		builder.Metadata.FindNavigation(NameOf(Customer.Projects)) _ 
			.SetPropertyAccessMode(PropertyAccessMode.Field)

	End Sub

End Class

The Customer class

Public NotInheritable Class Customer
  Private _Projects As HashSet(Of Project)

  Public ReadOnly Property Projects As IReadOnlyCollection(Of Project)
	Get
		Return _Projects
	End Get
  End Property

End Class

How the NavigationEntry is loaded

Sub LoadProjectCustomer(project as Project, context as DbContext)

	Dim custNavEnt = context.Entry(project).Navigations _ 
	.First(Function(e) e.Metadata.Name = "Customer")
	
	custNavEnt.Load()'<- Exception thrown here when called from COM object

End Sub

I am assuming that the issues is because it is being called from within a COM object. I could change how all the classes expose their navigation collections but I would rather not open up those collections even just within the namespace. I do not like to construct the collections in the Db entity class's constructor that is called by the Model Builder because having the navigation collections null is a good way to indicate if the entity has not had it's properties loaded and that it is not just a new entity with an empty collection.

Hello Mat Hat,

I copy-pasted your code and added the Entity Framework Core using this line in the Nuget Package Manager Console "Install-Package Microsoft.EntityFrameworkCore.SqlServer". It seems however there is an object called Project missing. Referred to in the line: "Sub LoadProjectCustomer(project As Project, context As DbContext)" and this code:

	Private _Projects As HashSet(Of Project)

	Public ReadOnly Property Projects As IReadOnlyCollection(Of Project)
		Get
			Return _Projects
		End Get
	End Property

yours,
Peter Swinkels