映射模型实体框架 4 代码优先

Question

谁能帮我定义使用 EF 4.3 的关系映射。尝试先在代码中对其进行建模时，我有点迷茫

逻辑在这里。

1. 一个城市有 1 个或多个位置（例如 1 区、CBD、南、北）
2. 一个位置有 0 个或多个场地
3. 场地可能属于 1 个地点（例如纽约 CBD 或纽约南部），或者如果城市较小且没有任何地点（例如夏威夷）和 1 个所有者，则属于 1 个城市
4. 显示市内场馆编号。如果一个城市有位置，则显示没有。所有地点的所有场地都属于城市。否则显示场馆数量仅属于该城市。

这是我的模型

public class City
{
    private ICollection<Location> _locations;
    private ICollection<Venue> _venues;

    public virtual int ID { get; set; }
    public virtual string Name { get; set; }

    public virtual ICollection<Location> Locations
    {
        get { return _locations ?? (_locations = new List<Location>()); }
        protected set { _locations = value; }
    }

    public virtual ICollection<Venue> Venues
    {
        get { return _venues ?? (_venues = new List<Venue>()); }
        protected set { _venues = value; }
    }
}

public class Location 
{
    private ICollection<Venue> _venues;

    public virtual int ID {get;set;}
    public virtual string Name { get; set; }

    public virtual int CityID{get;set;}
    public virtual City City {get;set;}

    public virtual ICollection<Venue> Venues
    {
        get { return _venues ?? (_venues = new List<Venue>()); }
        protected set { _venues = value; }
    }
}

public class Owner
{
    public virtual int ID {get;set;}
    public virtual string Name { get; set; }

    public virtual int VenueID {get;set;}
    public virtual Venue Venue {get;set;}
}

public class Venue
{
    public virtual int ID {get;set;}
    public virtual string Name { get; set; }

    public virtual int LocationID {get;set;}
    public virtual Location VenueLocation {get;set;}

    public virtual int VenueCityID{get;set;}
    public virtual City VenueCity {get;set;}

    public virtual int VenueOwnerID{get;set;}
    public virtual Owner VenueOwner {get;set;}
}

我尝试映射这些模型，但在尝试映射 Location、City 和 Venue 时非常混乱

public class Context : DbContext
{
    public DbSet<City> City{ get; set; }
    public DbSet<Locations> Locations{ get; set; }
    public DbSet<Owner> Owners{ get; set; }
    public DbSet<Venue> Venues{ get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Location>()
            .HasRequired(loc => loc.City)
                .WithMany(c => c.Locations)
                .HasForeignKey(loc => loc.CityID);

        modelBuilder.Entity<Venue>()
           .HasRequired(v => v.VenueOwner)
           .WithRequiredPrincipal();

        //confusing here when trying to map Location & City for this venue
        modelBuilder.Entity<Venue>()
           .HasRequired(v => v.Location)
           .WithRequiredPrincipal();

        modelBuilder.Entity<Venue>()
           .HasRequired(v => v.City)
           .WithRequiredPrincipal();
    }
}

Answer 1

如果您只坚持第 1 点和第 2 点中的陈述，您可能会发现它更简单。然后一个小城市将有一个位置集合，但只有一个条目。

此外，您的位置将有一个场馆集合，场馆将仅属于所有者和位置。

那么你会有：

public class City
{
    private ICollection<Location> _locations;

    public virtual int ID { get; set; }
    public virtual string Name { get; set; }

    public virtual ICollection<Location> Locations
    {
        get { return _locations ?? (_locations = new List<Location>()); }
        protected set { _locations = value; }
    }
}

public class Location 
{
    private ICollection<Venue> _venues;

    public virtual int ID {get;set;}
    public virtual string Name { get; set; }

    public virtual City City {get;set;}

    public virtual ICollection<Venue> Venues
    {
        get { return _venues ?? (_venues = new List<Venue>()); }
        protected set { _venues = value; }
    }
}

public class Owner
{
    public virtual int ID {get;set;}
    public virtual string Name { get; set; }

    public virtual int VenueID {get;set;}
    public virtual Venue Venue {get;set;}
}

public class Venue
{
    public virtual int ID {get;set;}
    public virtual string Name { get; set; }

    public virtual Location VenueLocation {get;set;}

    public virtual Owner VenueOwner {get;set;}
}

一个城市中所有场所的查询将如下所示：

city.Locations.SelectMany(l => l.Venues);