带有MySql的实体框架：将System.Guid映射到VARCHAR（40）

Question

I am using Entity Framework 6 code first to connect to a MySql database. I do not own the database. I cannot change the database schema. I also cannot change to another flavor of Entity Framework (model or database first).

I'm having trouble mapping my POCO object to a particular table

The table is as follows:

CREATE TABLE 'my_table' (
   'id' VARCHAR(40) NOT NULL,
   'name' VARCHAR(200),
   Primary Key ('id')
)

I know for a fact that the 'id' column will always be a Guid. Therefore I have created my POCO class as follows:

public class MyTable
{
   public Guid Id { get; set;}
   public string Name { get; set;}
}

From my understanding EF for MySql will only map VARCHAR columns to string fields in your POCO. Is there any way I can tell entity framework that the 'id' column should be converted from a VARCHAR(40) to a Guid?

I was thinking of accepting that I could not map to a Guid. I'd just map to a string and create a custom getter method:

public class MyTable
{
   public string Id { get; set;}
   public string Name { get; set;}

   public Guid GetId()
   {
       Guid id;
       if (Guid.TryParse(this.Id, out id))
            return id;
       else
            return new Guid();
   }
} 

Please help an EF newb out. Thanks

Answer 1

I could not find a way to do this. I was hoping that entity framework would just throw an exception if the VARCHAR(40) could not be parsed to a Guid. That is not the case with the MySQL provider.

I ended up declaring my Id member as a string. To keep my POCO class a true POCO class, I created a helper method to convert strings to Guids.

Answer 2

You may want to use interface for that and use explicit implementation.

public interface IMyTable
{
  Guid Id { get; set; }
  string Name { get; set; }
}

public class MyTable : IMyTable
{
  public string Id { get; set; }
  public string Name { get; set; }

  // use explicit implementation for Id
  Guid IMyTable.Id
  {
    get => Guid.Parse(this.Id);
    set => this.Id = value.ToString();
  }
}

So instead of using MyTable, you can use IMyTable to get object with fields that have the expected types.