Designing Model with foreign key - repository-pattern

Question

I am building an ORM by using Unit or Work and Repository using Dapper. I have searched the internet on this problem and no luck.
I have the following tables:
As you can see, Instance has Entity inside. I have 2 approaches:
Approach 1:
public class Entity
{
public int Id {get;set;}
public string Name {get;set;}
}
public class Instance
{
public int Id {get;set;}
public Entity Entity {get;set;}
public string Name {get;set;}
}
How can I get value for Entity with this approach?
Approach 2 (according to this link):
public class Entity
{
public int Id {get;set;}
public string Name {get;set;}
}
public class Instance
{
public int Id {get;set;}
public int EntityId {get;set;}
public string Name {get;set;}
}
Which design is better for use?

Answer 1

You can use QueryMultiple if you want to fetch the data from two different tables and fill it up in two different POCO classes. Following is copied from here:
string sql = "SELECT * FROM Invoice WHERE InvoiceID = #InvoiceID; SELECT * FROM InvoiceItem WHERE InvoiceID = #InvoiceID;";
using (var connection = My.ConnectionFactory())
{
connection.Open();
using (var multi = connection.QueryMultiple(sql, new {InvoiceID = 1}))
{
var invoice = multi.Read<Invoice>().First();
var invoiceItems = multi.Read<InvoiceItem>().ToList();
}
}
Both the models you mentioned in your code can be handled with this approach.
As an alternative approach, you can combine your two POCOs in one or you can use inheritance as well. But, looking at your data model, I do not think this is applicable to this particular case.
Which design is better for use?
Up to you. Whatever suits your project needs keeping down the unnecessary complexities is good for you.