peliculascontroller.cs

[HttpPost]
public async Task<ActionResult<int>> Post(Pelicula pelicula)
{
    if (!string.IsNullOrWhiteSpace(pelicula.Poster))
    {
        var poster = Convert.FromBase64String(pelicula.Poster);
        pelicula.Poster = await almacenadorArchivos.GuardarArchivo(poster,
            ".jpg", contenedor);
    }

    EscribirOrdenActores(pelicula);

    await AgregarPeliculaConSP(pelicula);
    //context.Add(pelicula);
    //await context.SaveChangesAsync();
    return pelicula.Id;
}

private async Task AgregarPeliculaConSP(Pelicula pelicula)
{
    // conexion con Dapper
    using var conn = new SqlConnection(connectionString);

    // insertar pelicula SP
    var id = await conn.QuerySingleAsync<int>($"InsertarPelicula", new
    {
        titulo = pelicula.Titulo,
        resumen = pelicula.Resumen,
        enCartelera = pelicula.EnCartelera,
        trailer = pelicula.Trailer,
        lanzamiento = pelicula.Lanzamiento?.ToString("yyyy-MM-dd"),
        poster = pelicula.Poster,
    },
        commandType: System.Data.CommandType.StoredProcedure);



    // insertar generos SP
    if (pelicula.GenerosPelicula is not null && pelicula.GenerosPelicula.Count > 0)
    {
        var generosPeliculas = pelicula.GenerosPelicula.Select(x => new { PeliculaId = id, x.GeneroId });

        await conn.ExecuteAsync($"InsertarGeneroPelicula", generosPeliculas,
        commandType: System.Data.CommandType.StoredProcedure);
    }


    // insertar actores SP

    // asignar pelicula Id
    pelicula.Id = id;
}

Procedimientos.sql

ALTER PROCEDURE InsertarGeneroPelicula
@peliculaId int,
@generoId int
AS
BEGIN
	-- SET NOCOUNT ON added to prevent extra result sets from
	-- interfering with SELECT statements.
	SET NOCOUNT ON;

    -- Insert statements for procedure here
	INSERT INTO GenerosPeliculas (PeliculaId, GeneroId)
	Values (@peliculaId, @generoId);
END
GO

ALTER PROCEDURE InsertarPelicula
 @Titulo nvarchar(max),
 @Resumen nvarchar(max) = NULL,
 @EnCartelera bit,
 @Trailer nvarchar(max) = NULL,
 @Lanzamiento datetime2 = NULL,
 @Poster nvarchar(max) = NULL
AS
BEGIN
	-- SET NOCOUNT ON added to prevent extra result sets from
	-- interfering with SELECT statements.
	SET NOCOUNT ON;

   INSERT INTO Peliculas (Titulo, Resumen, EnCartelera, Trailer, Lanzamiento, Poster)
   Values(@Titulo, @Resumen, @EnCartelera, @Trailer, @Lanzamiento, @Poster)

   SELECT SCOPE_IDENTITY();
END
GO