Can't insert entity Entity framework duplicate key exception

Question

I have context with Animal entity and Id as Identity column.

This is Animal definition:

public class Animal
{
    [Key, Column(Order = 0)]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int Id { get; set; }
    public string Name { get; set; }
}

There is only one animal in collection:

Animals: [{
    Id: 1,
    Name: "Dog"
  }].

I want to insert new Animal with following code:

context.Animals.Add(new Animal { Name: "Cat" })

Following exception is thrown:

System.InvalidOperationException: 'The instance of entity type 'Animal' cannot be tracked because another instance of this type with the same key is already being tracked.

Seems that EF already tracked Animal entity. You need to use already tracked entity to add new data (also provide part of code which throwing exception). — Tetsuya Yamamoto
– Tetsuya Yamamoto, Commented Apr 5, 2018 at 7:34
Apparently there is something not shown in the question. minimal reproducible example needed. — Ivan Stoev
– Ivan Stoev, Commented Apr 5, 2018 at 7:54

Gullard · Accepted Answer · 2018-04-05 08:07:14Z

2

Which database do you use? If it is InMemoryDatabase from Microsoft.EntityFrameworkCore.InMemory and first animal was added with explicit id (by context.Animals.Add(new Animal { Id: 1, Name: "Cat" })) then InMemoryDatabase does not increment internal identity counter used for id setting. So when you and second animal, InMemoryDatabase try to set Id to 1 but there is already animal with this id, so exception was thrown.

You have two solution:

Removed explicit id from first animal (I prefer this)
Explicity set id in second (and all next animals)

edited Apr 5, 2018 at 8:07

answered Apr 5, 2018 at 7:56

Gullard

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3 Comments

Mirhat Over a year ago

That is exactly what is happening

Gullard Over a year ago

So I add two possible solutions

Gert Arnold Over a year ago

Third option (strongly recommended): don't use InMemoryDatabase but test against an actual database (integration test). You shouldn't change code with the sole purpose to satisfy unit tests.

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