Code first EF in ASP.NET core Web API single primary key - asp.net-core-mvc

Question

I'm using an external library to return data to me, the library has a lot of fields in it and goes quite deep with nested objects.
My class looks something like this;
public class Dto
{
public Dto(Val val)
{
Val = val;
}
[Key]
public int Id { get; set; }
public Val Value{ get; set; }
}
And when trying to save the changes to EF I get the error;
Cannot insert explicit value for identity column in table 'Value' when IDENTITY_INSERT is set to OFF.
When looking through the migrations it appears as if the Primary Key has been set on a few properties within the Value object. I've looked and looked but can't find a way to stop the migration automatically assigning primary keys. I've found stuff such as in the example above using the;
[Key]
attribute and adding bits and pieces into the OnModelCreating override but nothing has came up with a successful result.
Edit to give some more clarity instead of an example.
[DbContext(typeof(SummonerDtoContext))]
[Migration("20180314210242_Migration8")]
partial class Migration8
{
protected override void BuildTargetModel(ModelBuilder modelBuilder)
{
#pragma warning disable 612, 618
modelBuilder
.HasAnnotation("ProductVersion", "2.0.2-rtm-10011")
.HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn);
modelBuilder.Entity("LccWebAPI.Models.SummonerDto", b =>
{
b.Property<int>("Id")
.ValueGeneratedOnAdd();
b.Property<long?>("SummonerId");
b.HasKey("Id");
b.HasIndex("SummonerId");
b.ToTable("Summoners");
});
modelBuilder.Entity("RiotSharp.SummonerEndpoint.Summoner", b =>
{
b.Property<long>("Id")
.ValueGeneratedOnAdd();
b.Property<long>("AccountId");
b.Property<long>("Level");
b.Property<string>("Name");
b.Property<int>("ProfileIconId");
b.Property<int>("Region");
b.Property<DateTime>("RevisionDate");
b.HasKey("Id");
b.ToTable("Summoner");
});
modelBuilder.Entity("LccWebAPI.Models.SummonerDto", b =>
{
b.HasOne("RiotSharp.SummonerEndpoint.Summoner", "Summoner")
.WithMany()
.HasForeignKey("SummonerId");
});
#pragma warning restore 612, 618
}
}
}
and my actual data object I'm trying to store;
public class SummonerDto
{
public SummonerDto(Summoner summoner)
{
Summoner = summoner;
}
public int Id { get; set; }
public Summoner Summoner { get; set; }
}
and my context;
public class SummonerDtoContext : DbContext
{
public SummonerDtoContext(DbContextOptions<SummonerDtoContext> options)
: base(options)
{ }
public DbSet<SummonerDto> Summoners { get; set; }
}
I don't have access to modify the inside of the Summoner object itself to add annotations to ignore them as keys.
And the model structure of the Summoner object which I have no access to amend;
public class Summoner : SummonerBase
{
[JsonProperty("profileIconId")]
public int ProfileIconId { get; set; }
[JsonConverter(typeof(DateTimeConverterFromLong))]
[JsonProperty("revisionDate")]
public DateTime RevisionDate { get; set; }
[JsonProperty("summonerLevel")]
public long Level { get; set; }
}
And the base;
public class SummonerBase
{
public Region Region { get; set; }
[JsonProperty("id")]
public long Id { get; set; }
public long AccountId { get; set; }
[JsonProperty("name")]
public string Name { get; set; }
}
Edit : RESOLVED
After 3 hours of trying to figure this out I've finally managed to solve it, since I don't have access to annotate the models directly, I'd previously tried accessing the Ids through my SummonerDto model. Instead I accecssed them directly and it's worked.
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<SummonerDto>()
.HasKey(c => c.Id);
modelBuilder.Entity<Summoner>().Property(x => x.Id).ValueGeneratedNever();
modelBuilder.Entity<Summoner>().Property(x => x.ProfileIconId).ValueGeneratedNever();
modelBuilder.Entity<SummonerBase>().Property(x => x.Id).ValueGeneratedNever();
base.OnModelCreating(modelBuilder);
}