.NET Core 6, one to many table for multiple tables-CodePudding

I have a medias table (for uploaded files), and many other tables which upload to this table.

Medias:

id, item_id, item_type, path

I want to have one-to-many relation between this table and others by item_id and item_type columns.

How should I define its ModelBuilder in OnModelCreating?

So when I say:

_db.Products.Include(x => x.Medias).FirstOrDefault(x => x.Id == 1)

it should select those medias with item_type of product and item_id of 1

CodePudding user response：

it should select those medias with "item_type" of product and "item_id" of 1

This is not a natural design for a relational database because there's no such thing as a "conditional foreign key". And EF is not going generate or leverage such a model.

If you create several many-to-many relationships, then EF will create several linking tables. You can make one of the FKs on a linking table unique if you want to model several one-to-many relationships.

CodePudding user response：

Fluent API for more details

example of one to many relationship

protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Student>()
                .HasOne<Grade>(s => s.Grade)
                .WithMany(g => g.Students)
                .HasForeignKey(s => s.CurrentGradeId);
        }
    
        public DbSet<Grade> Grades { get; set; }
        public DbSet<Student> Students { get; set; }