How to create foreign key relationships with the Entity Framework?

Question

I want to create a new row in my database on a table that has a couple of foreign key relationships and I haven't been able to get a handle on what order and what calls need to be made. This is what I have so far:

db.Models.Order order = DB.Models.Order.CreateOrder( apple );
order.CustomerReference.Attach( ( from c in db.Customer where c.Id == custId select c ).First() );
db.SaveChanges();

The code is failing on the second line there, saying:

Attach is not a valid operation when the source object associated with this related end is in an added, deleted, or detached state. Objects loaded using the NoTracking merge option are always detached.

Any ideas?

Jared · Accepted Answer · 2008-10-13 14:51:45Z

8

(Thanks John for the grammar fixes)

So I figured it out. This is what you have to do:

db.Models.Order order = DB.Models.Order.CreateOrder( apple );
order.Customer = (from c in db.Customer where c.Id == custId select c).First();
db.SaveChanges();

I hope that helps people.

answered Oct 13, 2008 at 14:51

Jared

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yojimbo87 · Accepted Answer · 2011-06-01 14:53:11Z

6

Why not use entity references? Your method will cause an extra SELECT statement.

A much nicer way is to use the CustomerReference class and an EntityKey.

order.CustomerReference = new System.Data.Objects.DataClasses.EntityReference<Customers>();
order.CustomerReference.EntityKey = new EntityKey("ModelsEntities.Customers", "Id", custId);

edited Jun 1, 2011 at 14:53

yojimbo87

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answered Dec 15, 2008 at 16:12

kirkmcpherson

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3 Comments

Jared Over a year ago

I wouldn't mind using your solution, but I would like to use strongly-typed database column names so I can get compile-time errors if the relationship is invalid.

jamiebarrow Over a year ago

I agree with kirkmcpherson, his way avoids doing the extra SELECT. I guess you value maintainable code over performance. You can still use his way, but instead of hard coded strings, you can use reflection to generate the strings by getting the class names for ModelsEntities and Customers in the above example. That way you get both one less SELECT, and strong typing / compile time errors. The added overhead from the reflection shouldn't be an issue IMO.

jamiebarrow Over a year ago

Okay, you can use reflection to generate the Entity Set name but not the Key name (i.e. can generate "ModelsEntities.Customers" using strong typing). Is there a way to generate the "Id" using reflection?

James Khoury · Accepted Answer · 2012-08-15 03:24:57Z

0

For update here is some sample code:

using (var ctx = new DataModelEntities())
{

       var result = (from p in ctx.UserRole.Where(o => o.UserRoleId == userRole.UserRoleId)
                              select p).First();

       result.RolesReference.EntityKey = new EntityKey("DataModelEntities.Roles",
                                       "RoleId", userRole.RoleId);

       result.UserRoleDescription = userRole.UserRoleDescription;      
       ctx.SaveChanges();
}

edited Aug 15, 2012 at 3:24

James Khoury

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answered Jun 14, 2009 at 14:24

VJ Koganti

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