Unable to track an entity of type because primary key property 'id' is null

问题

After I upgraded to Asp.Net Core 3.0 I am getting the following error for my Identity class when attempting to create a user:

Unable to track an entity 'User' of type because primary key property 'id' is null.

Here User represents my extension of the Identity model.

This is the line of code where the error occurs:

var result = await _userManager.CreateAsync(user, password);

回答1:

This is due to breaking changes in EF Core 3.0 which can be found under this link:

https://docs.microsoft.com/en-us/ef/core/what-is-new/ef-core-3.0/breaking-changes#string-and-byte-array-keys-are-not-client-generated-by-default

The problem can be solved by assigning a key manually like this:

// assign GUID to Id
user.Id = Guid.NewGuid().ToString();
var result = await _userManager.CreateAsync(user, password);

Another solution would be the following according to Microsoft:

The pre-3.0 behavior can be obtained by explicitly specifying that the key properties should use generated values if no other non-null value is set. For example, with the fluent API:

modelBuilder
    .Entity<Blog>()
    .Property(e => e.Id)
    .ValueGeneratedOnAdd();

Or with data annotations:

[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public string Id { get; set; }

回答2:

This solved the issue for me.

    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        var keysProperties = builder.Model.GetEntityTypes().Select(x => x.FindPrimaryKey()).SelectMany(x => x.Properties);
        foreach (var property in keysProperties)
        {
            property.ValueGenerated = ValueGenerated.OnAdd;
        }
    }

来源：https://stackoverflow.com/questions/59134406/unable-to-track-an-entity-of-type-because-primary-key-property-id-is-null