ef core 5 many to many example

Example 1: ef core many-to-many

class MyContext : DbContext
{
    public MyContext(DbContextOptions options)
        : base(options)
    {
    }

    public DbSet Posts { get; set; }
    public DbSet Tags { get; set; }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity()
            .HasMany(p => p.Tags)
            .WithMany(p => p.Posts)
            .UsingEntity(
                j => j
                    .HasOne(pt => pt.Tag)
                    .WithMany(t => t.PostTags)
                    .HasForeignKey(pt => pt.TagId),
                j => j
                    .HasOne(pt => pt.Post)
                    .WithMany(p => p.PostTags)
                    .HasForeignKey(pt => pt.PostId),
                j =>
                {
                    j.Property(pt => pt.PublicationDate).HasDefaultValueSql("CURRENT_TIMESTAMP");
                    j.HasKey(t => new { t.PostId, t.TagId });
                });
    }
}

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

    public ICollection Tags { get; set; }
    public List PostTags { get; set; }
}

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

    public ICollection Posts { get; set; }
    public List PostTags { get; set; }
}

public class PostTag
{
    public DateTime PublicationDate { get; set; }

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

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

Example 2: many to many ef core

protected override void OnModelCreating(ModelBuilder modelBuilder){    modelBuilder.Entity()        .HasKey(bc => new { bc.BookId, bc.CategoryId });      modelBuilder.Entity()        .HasOne(bc => bc.Book)        .WithMany(b => b.BookCategories)        .HasForeignKey(bc => bc.BookId);      modelBuilder.Entity()        .HasOne(bc => bc.Category)        .WithMany(c => c.BookCategories)        .HasForeignKey(bc => bc.CategoryId);}

Example 3: many to many ef core

public class Book{    public int BookId { get; set; }    public string Title { get; set; }    public Author Author { get; set; }    public ICollection Categories { get; set; }}   public class Category{    public int CategoryId { get; set; }    public string CategoryName { get; set; }    public ICollection Books { get; set; }}