如何在数据库中存储两个相同的实体？ 实体框架，C＃

Question

I have two entities with exactly the same properties:

public class Oil
{
    public Guid Id { get; set; }
    public string Title { get; set; }
    public int Price { get; set; }
    public int Ammount { get; set; }
}

public class Filter
{
    public Guid Id { get; set; }
    public string Title { get; set; }
    public int Price { get; set; }
    public int Ammount { get; set; }
}

Questions:

1) Can I somehow store them in one table? If so, than how?

2) Or should I implement inheritance? And what type then?

Edits:

In my case these two entities are just the same, they will not have any different properties in the future.

I implemented Table-per-Hierarchy approach, but there is another issue
(I have another type that has collections of oils and filters):

public class Warehouse
{
    public Guid Id { get; set; } 
    public ICollection<Filter> Filters { get; set; }
    public ICollection<Oil> Oils { get; set; }
}

So, when I create database, I get Warehouse_Id and Warehouse_Id1 fields in it. I don't want the Oil and Filter classes to have Warehouse property in them, how can I get just one field for Warehouse id in the db table?

If I include WarehouseId as a property in OilFilterBase class I will get 3 warehouse_id in the database table.

ps I also have DbSet<Oil> and DbSet<Filter> in my Context and don't have DbSet<OilFilterBase> .

Answer 1

It's hard to say what's best without knowing more about your requirements. What makes these two entities different? If they perform different functions and just happen to have the same properties, then it would probably be a good idea to store them in separate tables; that makes the most sense conceptually, and it would make things much easier if, say, you decided you wanted to add additional properties to one of them in the future.

On the other hand, if they're really the same at every level, it's also worth asking if you really need two different entity types to store them.

For the middle ground where the two classes serve related purposes but also differ in some ways, then yes, some form of inheritance might be a good approach -- either having one entity type derive from the other, or creating a new common base type and having both entities derive from that.

If you decide this is the best approach, then it looks like a good candidate for Table-per-Hierarchy mapping. You could restructure your code something like this:

public abstract class OilFilterBase
{
  public Guid Id { get; set; }
  public string Title { get; set; }
  public int Price { get; set; }
  public int Amount { get; set; }
}

public class Oil : OilFilterBase
{
}

public class Filter : OilFilterBase
{
}

...and then the Entity Framework will, by default, create a single table with an automatically-generated discriminator column, and store all instances of both entity types in that table.

If you decide that either of those entity types should have additional fields, then you could look at some of the other inheritance options, like Table-per-Type , that create separate but related tables for each entity type.

The first thing to do is decide how these classes fit together conceptually, and then figure out the best way to implement that in EF terms. If you can give more information about what these entities are and how they work, it'll be easier for people here to give good advice.

Response to Edits:

I think what's happening with the extra columns ( Warehouse_Id and Warehouse_Id1 ) is this:

Because you're setting up the relationships for Oil and Filter separately, it's not comfortable assuming you want to use the base class's WarehouseId property as the foreign key -- what if you only wanted to set up that relationship for Oil and not Filter ? It shouldn't be writing to the base class column in that case. So, it decides to create new properties instead.

Fortunately, you can use the [ForeignKey()] attribute (or the fluent API) to tell it what you really want, like this:

using System.ComponentModel.DataAnnotations.Schema;

public abstract class OilFilterBase
{
  public Guid Id { get; set; }
  public string Title { get; set; }
  public int Price { get; set; }
  public int Amount { get; set; }
  public Guid WarehouseId { get; set; }
}

public class Oil : OilFilterBase
{
}

public class Filter : OilFilterBase
{
}

public class Warehouse
{
  public Guid Id { get; set; }

  [ForeignKey("WarehouseId")]
  public virtual ICollection<Filter> Filters { get; set; }

  [ForeignKey("WarehouseId")]
  public virtual ICollection<Oil> Oils { get; set; }
}

Also, I think you'll need to include a DbSet<OilFilterBase> (in addition to DbSet<Oil> and DbSet<Filter> ) in your context in order to get Table-per-Hierarchy inheritance to work -- try it and see.

Good luck!