DatabaseContext.cs

using System;
using Microsoft.EntityFrameworkCore;

namespace CoreAPI.Models
{
    public class DatabaseContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) 
        => optionsBuilder.UseNpgsql("Host=localhost;Database=CoreAPIDb;Username=postgres;Password=1273");

        public DbSet<Author> Authors { get; set; }
        public DbSet<Book> Books { get; set; }
    }
}