EF 4.1 - Model Relationships

Question

I'm trying to create a quick ASP.NET MVC 3 application using the RC version of EF 4.1. I have two models:

public class Race
{
    public int RaceId { get; set; }
    public string RaceName { get; set; }
    public string RaceDescription { get; set; }
    public DateTime? RaceDate { get; set; }
    public decimal? Budget { get; set; }
    public Guid? UserId { get; set; }
    public int? AddressId { get; set; }

    public virtual Address Address { get; set; }
}

and

public class Address
{
    public int AddressId { get; set; }
    public string Street { get; set; }
    public string StreetCont { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public string ZipCode { get; set; }

    public virtual Race Race { get; set; }
}

I get the following error when trying to insert a new Race:

Unable to determine the principal end of an association between the types 'rcommander.Models.Race' and 'rcommander.Models.Address'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.

Shouldn't it recognize RaceId as the primary key of the Races table and AddressId as the FK to the Addresses table automatically? Am I missing something?

Thanks!

score 21 · Accepted Answer · edited Apr 20 '12 at 17:21

21

The problem here seems to be that EntityFramework can't recognize where the foreing key is, as you are holding cross references in both objects. Not being sure what you want to achieve, I may suggest something like this:

public class Race
{
  public int RaceId { get; set; }
  public string RaceName { get; set; }
  public string RaceDescription { get; set; }
  public DateTime? RaceDate { get; set; }
  public decimal? Budget { get; set; }
  public Guid? UserId { get; set; }

  public int? AddressId { get; set; }
  public virtual Address Address { get; set; }
}

public class Address
{
  public int AddressId { get; set; }
  public string Street { get; set; }
  public string StreetCont { get; set; }
  public string City { get; set; }
  public string State { get; set; }
  public string ZipCode { get; set; }
}

Skipping reference to Race in second entity.

edited Apr 20 '12 at 17:21

Albert Bori

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answered Mar 18 '11 at 13:09

tpeczek

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wont this remove navigational posibilities from Address though? – Yngve B-Nilsen Mar 18 '11 at 16:31
1

Yes it will remove navigation posibility from address and map it as one-to-many relation as I described in my answer. – Ladislav Mrnka Mar 18 '11 at 18:34
1

So is there a way to achieve (perhaps by attributes) the relationship in a cross reference? – Shimmy Weitzhandler May 11 '12 at 02:21
why do you actually need public int? AddressId { get; set; }? – Nikos Jan 25 '13 at 05:15

score 18 · Answer 2 · answered Mar 18 '11 at 13:30

18

The problem here is 1:1 relation between Address and Race! You probably want to map it as 1:N so you need to modify address to:

public class Address
{
  public int AddressId { get; set; }
  public string Street { get; set; }
  public string StreetCont { get; set; }
  public string City { get; set; }
  public string State { get; set; }
  public string ZipCode { get; set; }

  public virtual ICollection<Race> Races { ... }
}

If you want to use 1:1 then you can't use AddressId in Race but AddressId in Address must be foreign key of Race because entity framework can achive 1:1 only be "sharing" primary key.

answered Mar 18 '11 at 13:30

Ladislav Mrnka

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Can you please update your answer to show how to use 1:1 using shared primary key? I would like to have a bidirectional way of accessing like this: Race.Address and Address.Race. Keep Race and Address if possible in your example. Thanks. – Leniel Maccaferri Apr 27 '11 at 20:42
1

@Leniel: Check this answer: http://stackoverflow.com/questions/5388077/primary-foreign-key-in-entity-framework/5388658#5388658 I think it is what you are looking for. – Ladislav Mrnka Apr 27 '11 at 20:46

score 8 · Answer 3 · answered Jul 15 '12 at 21:09

For one-to-one relationship, you need to add "[required]" attribute in the second class. See below:

public class Race
{
  public int RaceId { get; set; }
  public string RaceName { get; set; }
  public string RaceDescription { get; set; }
  public DateTime? RaceDate { get; set; }
  public decimal? Budget { get; set; }
  public Guid? UserId { get; set; }

  public int? AddressId { get; set; }
  public virtual Address Address { get; set; }
 }

public class Address
{
 public int AddressId { get; set; }
 public string Street { get; set; }
 public string StreetCont { get; set; }
 public string City { get; set; }
 public string State { get; set; }
 public string ZipCode { get; set; }

 [required]
 public Race Race { get; set; }

}

score 5 · Answer 4 · answered Apr 20 '11 at 21:10

5

There is a good post: Associations in EF Code First CTP5: Part 2 – Shared Primary Key Associations

http://weblogs.asp.net/manavi/archive/2010/12/19/entity-association-mapping-with-code-first-one-to-one-shared-primary-key-associations.aspx

answered Apr 20 '11 at 21:10

Roeland Jimenez

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"One way to turn our associations to be one-to-one is by making them bidirectional. That is, adding a new navigation property to Address class of type User and another one of type Shipment. " - this does not seem to work. I get a "Unable to determine the principal end of an association between the types ... The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations." – Karan Oct 02 '12 at 16:28

Yngve B-Nilsen · Answer 5 · 2011-03-18T13:27:40.813

4

It recognizes Id as the primary key by convention. So what you need to do:

public class Race
{
    [Key]
    public int RaceId { get; set; }
    public string RaceName { get; set; }
    public string RaceDescription { get; set; }
    public DateTime? RaceDate { get; set; }
    public decimal? Budget { get; set; }
    public Guid? UserId { get; set; }
    public int? AddressId { get; set; }

    public virtual Address Address { get; set; }
}
and

public class Address
{
    [Key]
    public int AddressId { get; set; }
    public string Street { get; set; }
    public string StreetCont { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public string ZipCode { get; set; }

    [ForeignKey("RaceId")] // Maybe telling it what the ForeignKey is will help?
    public virtual Race Race { get; set; }
}

The [Key] attribute indicates that it should be the PrimaryKey

If you don't want this, you need to rename your primary keys to simply public int Id {get; set; }

edited Mar 18 '11 at 13:27

answered Mar 18 '11 at 12:38

Yngve B-Nilsen

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Same error using either method. I have my DB Initializer in Application_Start in Global.asax to DropCreateDatabaseIfModelChanges if that matters. – Mike Mar 18 '11 at 12:47
1

Hmm... Check my update.. Maybe the ForeignKeyAttribute is what you need? – Yngve B-Nilsen Mar 18 '11 at 13:27
1

Isnt InverseProperty("RaceId") what is needed here, not ForeignKey? – Joe Dec 02 '11 at 09:15
Assuming we have InverseProperty("RaceId") - could you have: var address = new Address(); var race = new Race(){Address = address} - and then obtain race via address.Race? – Karan Oct 02 '12 at 16:18

Thanasis Ioannidis · Answer 6 · 2012-08-21T12:36:17.823

I think it would be solved also like this... I assumed that an address is not required to be associated with a race, but a race must always be associated with an address. I had the same problem with Patients and Incidents and i solved it with InverseProperty which is actually the same with foreign key, but the other direction

public class Race
{
  public int RaceId { get; set; }
  public string RaceName { get; set; }
  public string RaceDescription { get; set; }
  public DateTime? RaceDate { get; set; }
  public decimal? Budget { get; set; }
  public Guid? UserId { get; set; }

  public int AddressId { get; set; }

  [ForeignKey("AddressId")]
  public virtual Address Address { get; set; }
 }

public class Address
{
 public int AddressId { get; set; }
 public string Street { get; set; }
 public string StreetCont { get; set; }
 public string City { get; set; }
 public string State { get; set; }
 public string ZipCode { get; set; }

 public int? RaceId { get; set; }
 [InverseProperty("RaceId")]
 public Race Race { get; set; }

}

EF 4.1 - Model Relationships

6 Answers6

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