如何在多对多关系中保存EF Core 3.1.3中的更改？

// 定义连接表实体对象
public class Relationship
{
    public int Entity1Id { get; set; }
    public int Entity2Id { get; set; }

    public virtual Entity1 Entity1 { get; set; }
    public virtual Entity2 Entity2 { get; set; }
}

// 定义相关实体对象
public class Entity1
{
    public int Id { get; set; }
    public string Name { get; set; }

    [InverseProperty("Entity1")]
    public virtual ICollection<Relationship> Relationships { get; set; }
}

public class Entity2
{
    public int Id { get; set; }
    public string Name { get; set; }

    [InverseProperty("Entity2")]
    public virtual ICollection<Relationship> Relationships { get; set; }
}

// 在DbContext中添加DbSet和连接表实体集合
public class MyDbContext : DbContext
{
    public DbSet<Entity1> Entity1s { get; set; }
    public DbSet<Entity2> Entity2s { get; set; }
    public DbSet<Relationship> Relationships { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Relationship>()
            .HasKey(r => new { r.Entity1Id, r.Entity2Id });

        modelBuilder.Entity<Relationship>()
            .HasOne(r => r.Entity1)
            .WithMany(e => e.Relationships)
            .HasForeignKey(r => r.Entity1Id);

        modelBuilder.Entity<Relationship>()
            .HasOne(r => r.Entity2)
            .WithMany(e => e.Relationships)
            .HasForeignKey(r => r.Entity2Id);
    }
}

// 在保存更改时创建连接表实体对象并添加到DbContext中
using (var context = new MyDbContext())
{
    var entity1 = new Entity1 { Name = "Entity 1" };
    var entity2 = new Entity2 { Name = "Entity 2" };

    context.Entity1s.Add(entity1);
    context.Entity2s.Add(entity2);

    var relationship = new Relationship
    {
        Entity1 = entity1,
        Entity2 = entity2
    };

    context.Relationships.Add(relationship);

    context.SaveChanges();
}