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

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

Code:

---

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

Code:

---

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

Code:

---

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

Code:

---

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.

Quote:

---

Originally Posted by 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

Code:

---

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

Code:

---

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

Code:

---

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

Code:

---

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:

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