Ef core code first Error: Key ("Id")=(33) already exists

Question

I am doing a crud for Destinations table in a asp.net core project. ( using ef core code first method )

when create a new Destinations I got error in debug console like this.

Exception data:
    MessageText: duplicate key value violates unique constraint "PK_Destinations"
    Detail: Key ("Id")=(33) already exists.
    SchemaName: public
    TableName: Destinations
    ConstraintName: PK_Destinations

For some reasons We have already create a Destinations table and added data manually. And now doing a crud for that table . I guess that's why this error Key ("Id")=(33) already exists. occurs.

DbContext.cs

public DbSet<Destination> Destinations { get; set; }

service.Cs

  public async Task<Destination> Create(Destination destination)
        {
            await _catalogDbContext.Destinations.AddAsync(destination);
            await _catalogDbContext.SaveChangesAsync();
            return destination;
        }

My Question is

• I have 100 rows in my table. We can not remove them. So destination id should start from 301 when adding new destination.

• Our development Database has 200 rows in our table. We can not remove them. So destination id should start from 201 when adding new destination.

• Our production Database has 240 rows in our table. We can not remove them. So destination id should start from 241 when adding new destination.

How can I do, when create a destination Id should starting from 101, 201 or 241. And The id should increase automatically after a new one is added.?

Edit: Destination.cs

public class Destination
    {
        [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; private set; }

        [Required]
        public string Continent { get; set; }

        [Required]
        public string Country { get; set; }

        [Required]
        public string Iso { get; set; }

        [Required]
        public string Name { get; set; }
}

Answer 1

it seems that key id =33 already exist in table and you cannot add duplicate as its primary key.

you can set identity value for Id column using DBCC command

1. check current seed: DBCC CHECKIDENT ('yourtablename');
2. set new seed; DBCC CHECKIDENT ('yourtablename', RESEED, 200);

then run your code.

Answer 2

When you add a new entity, it's better to let Id value as default value, don't try to assign it. (For example, Id is int so let the value = 0)

public async Task<Destination> Create()
{
     var destination = new Destination
     {
        Continent = "What ever",
        Country = "...."
        // Init all required properties BUT Id
     };

     // At this line, destination.Id == 0 because you didn't assign a value
     await _catalogDbContext.Destinations.AddAsync(destination);
     await _catalogDbContext.SaveChangesAsync();

     // At this line, you should see destination.Id > 0, the value is assigned by EntityFramework
     return destination;
}

Answer 3

There is no issue with code snippet you have mentioned here. need to work on database side.

what i understood is, your table having pk column id which is identity ie auto increment. in such case you need to reseed it. for ex. if your table having existing records then you need to get max value of id column; let say id column max value is 200. now you have to tell database to set the identity to 200. next time, when new record inserted it will be stored with id=201 and so on.

step to reseed table identity value is as below

DBCC CHECKIDENT ('yourtablename', RESEED, 200)

https://docs.microsoft.com/en-us/sql/t-sql/database-console-commands/dbcc-checkident-transact-sql?view=sql-server-ver15