defining foreign key relationship

Question

User364607740 posted

Lets say there are two model classes,

public class ClassA
{
	public int AId { get; set; }
	...
}

public class ClassB
{
	public int BId { get; set; }
	...
}

If I have to show foreign key relationship from ClassA to ClassB, there are two approaches,

public class ClassB
{
	public int BId { get; set; }
	...
	[ForeignKey("AId")]
        public ClassA ClassAs { get; set; } 
        public int AId { get; set; } 
}
or
public class ClassB
{
	public int BId { get; set; }
	...
	[ForeignKey("AId")]
	public ICollection<ClassA> ClassAs { get; set; }
}

What is the difference in these two types of foreign key relationship?

Answer 1

User475983607 posted

Navigation property syntax is openly covered in the Entity Framework fundamentals.  Please read the docs for the version of entity framework you are using rather than posting the same information on the forums.

EF Core

https://docs.microsoft.com/en-us/ef/core/modeling/relationships?tabs=fluent-api%2Cfluent-api-simple-key%2Csimple-key

EF 6

https://docs.microsoft.com/en-us/ef/ef6/fundamentals/relationships

Answer 2

User1686398519 posted

Hi scala_1988,

1. The [ForeignKey] attribute is used to override the default convention of foreign keys. It allows us to specify foreign key attributes in subordinate entities whose names do not match the primary key attributes of the principal entity.
2. The two writing methods you mentioned are just two different methods of setting [ForeignKey].
3. "ICollection<ClassA> ClassAs" is a collection navigation property that contains references to many related entities. "ClassA ClassAs" is a reference navigation attribute that contains a reference to a single related entity.

Best Regards,

YihuiSun

Answer 3

User364607740 posted

Thank You for explaining the topics. Thank you very much...