Entity Framework Core 6: Querying with Navigation Properties Leading to Unexpected Nulls
I just started working with I'm learning this framework and I'm currently using Entity Framework Core 6 with a SQL Server backend, and I've run into an issue where querying entities with navigation properties sometimes returns null values unexpectedly. For example, I have two entities, `Order` and `Customer`, where `Order` has a foreign key reference to `Customer`. My query looks like this: ```csharp var orders = await _context.Orders.Include(o => o.Customer).ToListAsync(); ``` The `Customer` entity is being included, but there are cases when the `Customer` property of some `Order` instances is null, even though those orders should have associated customers based on the foreign key relationship. I've verified that the foreign key values are correct in the database. I've also checked the navigation properties in the `Order` class. Here are the relevant parts of my entity classes: ```csharp public class Order { public int Id { get; set; } public int CustomerId { get; set; } public Customer Customer { get; set; } } public class Customer { public int Id { get; set; } public string Name { get; set; } public ICollection<Order> Orders { get; set; } } ``` To troubleshoot, I tried loading the orders without the `Include` and then manually fetching the customer data, but it resulted in the same null values: ```csharp var orders = await _context.Orders.ToListAsync(); foreach (var order in orders) { var customer = await _context.Customers.FindAsync(order.CustomerId); // This also returns null for some orders } ``` I also examined the database directly and confirmed that the `CustomerId` in the `Orders` table aligns with valid `Id`s in the `Customers` table. I suspect it might be related to tracking or lazy loading, but I'm not using lazy loading in my setup. Could this issue be related to how EF Core manages tracking for relationships, or is there a possibility of data integrity issues that I'm overlooking? Any insights would be greatly appreciated! The project is a CLI tool built with C#. For context: I'm using C# on Ubuntu 20.04. Any feedback is welcome!