使用实体框架V1更新外键（实体）

Question

I have a small ASP.NET MVC application with the following entity objects:

Person

• PersonId
• Name (string)
• FirstName (string)
• Country (Country)

Country

• CountryId
• Name

I can add and delete the entity's this works fine. I can also update name, firstname. But how can i update the country property with another country.

i was trying

p.Country = (from c in db.Country 
             where c.CountryId == countryId 
             select c).First();

but this fires an exception {"An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key."}"

even before i call SaveChanges on the datacontext.

Can someone explaind how i can update this property?

kind regards Dieter

Answer 1

Is db your context? You should be able to do:

p.Country = ctx.Country.First(c => c.CountryId == countryId);

Or, if you don't want to query the database to get the foreign key entity you can also use an EntityKey to the same effect:

p.CountryReference.EntityKey = new EntityKey("MyDb.Country", "CountryId", countryId);

Answer 2

我使用了第二个解决方案，但我没有例外，但是在调用AcceptChanges之后，CountryId在数据库中没有被更改。

Answer 3

Code similar to this has worked for me when updating navigation properties.

   Country country = new Country{CountryId = theNewCountryID };
    db.AttachTo("Countries", country);
    p.Country = country;
    db.Savechanges();

Create a stub of the new country then attach it to the countries EntitySet, assign the new country to your Entity's navigational country property and call SaveChanges(). Use your country EntitySet name in the AttachTo call.

Answer 4

This is what worked for me. In the model:

<%= Html.Textbox("Country.CountryId", Model.Countries) %> // I'm using a form model view

In the controller:

Person originalPerson = (from p in db.PersonSet
                        where p.PersonId == updatedPerson.PersonId
                        select p).First();

Country country = (from c in db.CountrySet 
                  where c.CountryId == updatePerson.Country.CountryId 
                  select c).First();

db.Attach(country);
originalPerson.Country = country;
db.ApplyPropertyChanges(originalPerson.EntityKey.EntitySetName, updatedPerson);
db.Savechanges();