Unable save or read data with Many-to-Many relationship in MySql

[vikasjain6]

hi, i was trying to use with blow sample code DbContext and usage code

public class Many2ManyDbContext : DbContext { private string _connectionString = string.Empty; public Many2ManyDbContext(string connectionString) { this._connectionString = connectionString; } public DbSet<Post> Posts { get; set; } public DbSet<Tag> Tags { get; set; } public DbSet<PostTag> PostTags { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        //optionsBuilder.Usesq(@"Server=(localdb)\mssqllocaldb;Database=MyDatabase;Trusted_Connection=True;");
        optionsBuilder.UseMySql(this._connectionString);

    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<PostTag>()
            .HasKey(t => new { t.PostId, t.TagId });

        modelBuilder.Entity<PostTag>()
            .HasOne(pt => pt.Post)
            .WithMany(p => p.PostTags)
            .HasForeignKey(pt => pt.PostId);

        modelBuilder.Entity<PostTag>()
            .HasOne(pt => pt.Tag)
            .WithMany(t => t.PostTags)
            .HasForeignKey(pt => pt.TagId);
    }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }

    public List<PostTag> PostTags { get; set; }
}

public class Tag
{
    public string TagId { get; set; }

    public List<PostTag> PostTags { get; set; }
}

public class PostTag
{
    public int PostId { get; set; }
    public Post Post { get; set; }

    public string TagId { get; set; }
    public Tag Tag { get; set; }
}

using (var context = new Many2ManyDbContext(@"Server=localhost;database=BlogPostMany2;uid=root;pwd=mysql2016;")) { context.Database.EnsureCreated();

            foreach (var item in context.PostTags.Include(p => p.Post).Include(t => t.Tag))
            {
                Console.WriteLine($"Tag:\n\t TagId:{item.Tag.TagId}");
                Console.WriteLine($"Post:\n\tTitle:{item.Post.Title} \t\tContent: {item.Post.Content}");
            }

            var tag = new Tag { TagId = Guid.NewGuid().ToString() };
            var post = new Post { Title = "Intro to C#", Content = "Just testing" };
            var postTage = new PostTag { Tag = tag, Post = post };

            context.PostTags.Add(postTage);
            context.SaveChanges();

            foreach (var item in context.PostTags.Include(p => p.Post).Include(t => t.Tag))
            {
                Console.WriteLine($"Tag:\n\t TagId:{item.Tag.TagId}");
                Console.WriteLine($"Post:\n\tTitle:{item.Post.Title} \t\tContent: {item.Post.Content}");
            }
        }

[mylemans]

@vikasjain6 And the error? What is the result of this code for you?

[mguinness]

It would also be worth trying this with EF Core 1.1 now as that has many improvements.