C#•2y ago

❔ one to zero or one relationship EFC

How can I model a 1:cn relationship in Entity Framework Core? E.g. An employee either has a supervisor or not

12 Replies

Tvde1•2y ago

https://learn.microsoft.com/en-us/ef/core/modeling/relationships explains a lot!

Relationships - EF Core

How to configure relationships between entity types when using Entity Framework Core

Tvde1•2y ago

you might just need

class Employee
{
    public int Id { get; set; }

    public Employee? Manager { get; set; }
}

class Employee
{
    public int Id { get; set; }

    public Employee? Manager { get; set; }
}

And it will create a FK for you

moritz•2y ago

if i do _db.Employees.Include(e => e.Manager) it filters out employees without managers. how can you avoid that?

Tvde1•2y ago

it doesn't filter out anything it makes is to when the query runs, it will also fetch the person's managers if you omit the Include, the .Manager will be null for everybody, because EF by default does not load all references if it would always do that, it would make a lot of queries slow when the properties are not used

moritz•2y ago

it uses an inner join in the compiled sql query apparently, that would explain why its filtered for me

Tvde1•2y ago

that is very odd

moritz•2y ago

only difference is that i have the new-ish #nullable disabled so i dont have the question mark after the type name

Tvde1•2y ago

I'm pretty sure it does not inner join

Tvde1•2y ago

linqpad shows a left join

Tvde1•2y ago

you can output the generated SQL on an IQueryable<T> with .ToQueryString()

moritz•2y ago

now it works correctly, weird. i swear yesterday it didnt

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

Gaming

Programming

❔ one to zero or one relationship EFC