Is it possible to create a table in Entity Framework Core without defining a key?

Yes, you can create a table without a primary key in Entity Framework Core, but it's generally not recommended. Entity Framework Core expects each entity to have a primary key for tracking and identifying entities efficiently. However, there might be certain situations where you need to map to a table without a primary key, such as mapping to a view or a table from a legacy database.

To map to a table without a primary key, you would typically use the HasNoKey method in your OnModelCreating method within your DbContext class. Here's an example:

using Microsoft.EntityFrameworkCore;

public class YourDbContext : DbContext
{
    public DbSet<YourEntity> YourEntities { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<YourEntity>().HasNoKey();
    }
}

public class YourEntity
{
    // Define your properties here
    public int SomeProperty { get; set; }
    public string AnotherProperty { get; set; }
}

In this example, YourEntity does not have a primary key defined explicitly, and the HasNoKey method is used to configure that the entity does not have a key. However, be cautious when using tables without primary keys, as it might lead to unexpected behavior, especially with insert, update, and delete operations.

If possible, it's generally recommended to have a primary key defined for each entity in your database schema for better data integrity and performance.