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I'm playing with the Entity Framework model designer, and I've got a question about creating entity associations:

In the "create association" dialog, when I create a 1:many association, it offers this checkbox:

"Add foreign key properties to the [entityname] entity"

I've been checking this box and I get results that are expected and make sense to me: Clicking the navigation property in the diagram highlights the related field in both entities that tie them together.

But, what would it mean not to check this box? I've tried this, and I then see no place in the entity to store a reference to the parent table's primary id. Am I correct that the navigation properties don't store any data in the database? If so, how could this work? Am I, perhaps, expected to manually map the navigation property to an Int32 field on the entity?

David Silva-Barrera
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BenjiFB
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  • FYI, I just tried having two entities, no constraints on the association. It seems that EF will automatically create a field [parent_id] on the child table. – BenjiFB Oct 08 '13 at 14:54

1 Answers1

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Associations represent relationship between entities. In the database (relational model) these relations are modeled by using foreign keys and - in the case of many-to-many - a join table. In the object model relations are typically modeled as references to the related object (in EF they are often referred to as Navigation Properties). The problem arises when you need to create or modify a relationship in the object model - you always need to have a reference of the related object you would like to set. In a pure object model this usually is not a problem but in case of ORM it means that if you don't have the related entity you need to send a query to the database to get the object to be able to set the reference to. However oftentimes - even if you don't have the related entity - you know the Id of the related entity. So, if the foreign key properties were exposed (and handled) in your object model you could create or modify a relationship without having to send additional queries to the database. This is what the checkbox is about. If you check it your entities will have (extraneous from object model perspective) properties mapped to foreign key columns in the database which you can use to manipulate relationships.

Pawel
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