Add data for many to many by reusing the same data from table

Goal: apply data in the tables [Movies], [GenreMovie] and [Genres] in an efficent approach (high performance).

Problem: when you need to reuse the data that is already existing in the database by using Id but you get this error:

The instance of entity type 'Genre' cannot be tracked because another instance with the same key value for {'GenreId'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.

From this piece of code

_schoolContext.AddRange("

        else
        {
            var comedy = new Genre() { GenreId = genreAsDictionary["Comedy"] };
            var action = new Genre() { GenreId = genreAsDictionary["Action"] };

            // Bug here
            _schoolContext.AddRange(
                new Movie() { Name = "Test test", GenresGenres = new List<Genre>() { comedy, action } });

            _schoolContext.SaveChanges();
        }

I do not want another duplicate of same data that is already existing in the database.

How should I solve this situation?

Thank you!

Source code: https://www.learnentityframeworkcore5.com/whats-new-in-ef-core-5/many-to-many-relationship

using Microsoft.AspNetCore.Mvc;
using WebApplicationStudent.Database;

namespace WebApplicationStudent.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private readonly ILogger<WeatherForecastController> _logger;
        private readonly SchoolContext _schoolContext;
        private readonly Repo _repo;

        public WeatherForecastController(ILogger<WeatherForecastController> logger, SchoolContext schoolContext, Repo repo)
        {
            _logger = logger;
            _schoolContext = schoolContext;
            _repo = repo;
        }

        [HttpGet(Name = "AddData")]
        public async Task<int> Get()
        {
            try
            {
                //_schoolContext.Database.EnsureCreated();

                var genreAsDictionary = await _repo.GetGenre();
                var movieAsDictionary = await _repo.GetMovie();

                if (!genreAsDictionary.Any() && !movieAsDictionary.Any())
                {
                    var comedy = new Genre() { GenreName = "Comedy" };
                    var action = new Genre() { GenreName = "Action" };
                    var horror = new Genre() { GenreName = "Horror" };
                    var scifi = new Genre() { GenreName = "Sci-fi" };

                    _schoolContext.AddRange(
                        new Movie() { Name = "Avengers", GenresGenres = new List<Genre>() { action, scifi } },
                        new Movie() { Name = "Ants", GenresGenres = new List<Genre>() { action, scifi } },
                        new Movie() { Name = "Satanic Panic", GenresGenres = new List<Genre>() { comedy, horror } });

                    _schoolContext.SaveChanges();
                }
                else
                {
                    var comedy = new Genre() { GenreId = genreAsDictionary["Comedy"] };
                    var action = new Genre() { GenreId = genreAsDictionary["Action"] };

                    // Bug here
                    _schoolContext.AddRange(
                        new Movie() { Name = "Test test", GenresGenres = new List<Genre>() { comedy, action } });

                    _schoolContext.SaveChanges();
                }
            }
            catch (Exception ex) 
            {
                int ff = 23;
            }

            return 1;
        }
    }
}

using Microsoft.EntityFrameworkCore;
using WebApplicationStudent.Controllers;
using WebApplicationStudent.Database;

namespace WebApplicationStudent
{
    public class Repo
    {
        private readonly ILogger<WeatherForecastController> _logger;
        private readonly SchoolContext _schoolContext;

        public Repo(ILogger<WeatherForecastController> logger, SchoolContext schoolContext)
        {
            _logger = logger;
            _schoolContext = schoolContext;
        }

        public async Task<Dictionary<string, int>> GetGenre()
        {
            return await _schoolContext.Genres.ToDictionaryAsync(a => a.GenreName ?? "", a => a.GenreId);
        }

        public async Task<Dictionary<string, int>> GetMovie()
        {
            return await _schoolContext.Movies.ToDictionaryAsync(a => a.Name ?? "", a => a.MovieId);
        }
    }
}

Scaffold-DbContext "Server=DESKTOP-TCK\MSSQLSERVER2022;Database=Testtest2;Integrated Security=true;Trusted_Connection=True;MultipleActiveResultSets=true;TrustServerCertificate=true;" Microsoft.EntityFrameworkCore.SqlServer -OutputDir "Database" -ContextDir "Database" -DataAnnotations -Context SchoolContext -NoOnConfiguring -WarningAction:SilentlyContinue -Force -Project WebApplicationStudent -StartupProject WebApplicationStudent -schema dbo

CREATE TABLE [dbo].[Movies] (
    [MovieId] INT            IDENTITY (1, 1) NOT NULL,
    [Name]    NVARCHAR (MAX) NULL,
    CONSTRAINT [PK_Movies] PRIMARY KEY CLUSTERED ([MovieId] ASC)
);

CREATE TABLE [dbo].[Genres] (
    [GenreId]   INT            IDENTITY (1, 1) NOT NULL,
    [GenreName] NVARCHAR (MAX) NULL,
    CONSTRAINT [PK_Genres] PRIMARY KEY CLUSTERED ([GenreId] ASC)
);

CREATE TABLE [dbo].[GenreMovie] (
    [GenresGenreId] INT NOT NULL,
    [MoviesMovieId] INT NOT NULL,
    CONSTRAINT [PK_GenreMovie] PRIMARY KEY CLUSTERED ([GenresGenreId] ASC, [MoviesMovieId] ASC),
    CONSTRAINT [FK_GenreMovie_Genres_GenresGenreId] FOREIGN KEY ([GenresGenreId]) REFERENCES [dbo].[Genres] ([GenreId]) ON DELETE CASCADE,
    CONSTRAINT [FK_GenreMovie_Movies_MoviesMovieId] FOREIGN KEY ([MoviesMovieId]) REFERENCES [dbo].[Movies] ([MovieId]) ON DELETE CASCADE
);

using Microsoft.EntityFrameworkCore;
using WebApplicationStudent;
using WebApplicationStudent.Database;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddTransient<Repo>();

builder.Services.AddDbContext<SchoolContext>(options =>
options.UseSqlServer("Server=DESKTOP-TCK\\MSSQLSERVER2022;Database=Testtest2;Trusted_Connection=True;TrustServerCertificate=True;MultipleActiveResultSets=true;"));



var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();
app.UseAuthorization();

app.MapControllers();

app.Run();