Kavita/API/Data/DataContext.cs

using API.Entities;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore;

namespace API.Data
{
    public class DataContext : IdentityDbContext<AppUser, AppRole, int, 
        IdentityUserClaim<int>, AppUserRole, IdentityUserLogin<int>,
        IdentityRoleClaim<int>, IdentityUserToken<int>>
    {
        public DataContext(DbContextOptions options) : base(options)
        {
            
        }
        public DbSet<Library> Library { get; set; }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);

            builder.Entity<AppUser>()
                .HasMany(ur => ur.UserRoles)
                .WithOne(u => u.User)
                .HasForeignKey(ur => ur.UserId)
                .IsRequired();
            
            builder.Entity<AppRole>()
                .HasMany(ur => ur.UserRoles)
                .WithOne(u => u.Role)
                .HasForeignKey(ur => ur.RoleId)
                .IsRequired();
        }
    }
}