I have 2 classes: Client and Survey.
Each Client can have many surveys - but only one default survey.
I have defined the classes like this:
public class Client
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }
public string ClientName { get; set; }
public Nullable<int> DefaultSurveyID { get; set; }
[ForeignKey("DefaultSurveyID")]
public virtual Survey DefaultSurvey { get; set; }
public virtual ICollection<Survey> Surveys { get; set; }
}
public class Survey
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }
public string SurveyName { get; set; }
[Required]
public int ClientID { get; set; }
[ForeignKey("ClientID")]
public virtual Client Client { get; set; }
}
This creates the Client table as I expect:
[dbo].[Clients]
(
[ID] [int] IDENTITY(1,1) NOT NULL,
[ClientName] [nvarchar](max) NULL,
[DefaultSurveyID] [int] NULL
)
But the Survey table has an extra foreign key:
[dbo].[Surveys]
(
[ID] [int] IDENTITY(1,1) NOT NULL,
[SurveyName] [nvarchar](max) NULL,
[ClientID] [int] NOT NULL,
[Client_ID] [int] NULL
)
Why is Code First generating this relationship and how to I tell it not to?
The problem is that when you have multiple relationships between two entities, EF Code First isn't able to find out which navigation properties match up, unless, you tell it how, here is the code:
public class Client
{
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ID { get; set; }
public string ClientName { get; set; }
/****Change Nullable<int> by int?, looks better****/
public int? DefaultSurveyID { get; set; }
/****You need to add this attribute****/
[InverseProperty("ID")]
[ForeignKey("DefaultSurveyID")]
public virtual Survey DefaultSurvey { get; set; }
public virtual ICollection<Survey> Surveys { get; set; }
}
With your previous version, EF was creating that extra relationship because it didn't know that the DefaultSurvey
property was referencing the ID
of the Survey
class, but you can let it know that, adding the attribute InverseProperty
whose parameter is the name of the property in Survey
you need DefaultSurvey
to match with.
You can do it using code-first, but not being a code first expert I cheated :-)
1) I created the tables and relationships (as above without the extra Client_ID) in the database using SMS
2) I used Reverse Engineer Code First to create the required classes and mappings
3) I dropped the database and recreated it using context.Database.Create()
Original table defs:
CREATE TABLE [dbo].[Client](
[Id] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](50) NULL,
[DefaultSurveyId] [int] NULL,
CONSTRAINT [PK_dbo.Client] PRIMARY KEY NONCLUSTERED
(
[Id] ASC
)
)
CREATE TABLE [dbo].[Survey](
[Id] [int] IDENTITY(1,1) NOT NULL,
[Name] [nvarchar](50) NULL,
[ClientId] [int] NULL,
CONSTRAINT [PK_dbo.Survey] PRIMARY KEY NONCLUSTERED
(
[Id] ASC
)
)
Plus foreign keys
ALTER TABLE [dbo].[Survey] WITH CHECK
ADD CONSTRAINT [FK_dbo.Survey_dbo.Client_ClientId] FOREIGN KEY([ClientId])
REFERENCES [dbo].[Client] ([Id])
ALTER TABLE [dbo].[Client] WITH CHECK
ADD CONSTRAINT [FK_dbo.Client_dbo.Survey_DefaultSurveyId]
FOREIGN KEY([DefaultSurveyId]) REFERENCES [dbo].[Survey] ([Id])
Code generated by reverse engineering:
public partial class Client
{
public Client()
{
this.Surveys = new List<Survey>();
}
public int Id { get; set; }
public string Name { get; set; }
public int? DefaultSurveyId { get; set; }
public virtual Survey DefaultSurvey { get; set; }
public virtual ICollection<Survey> Surveys { get; set; }
}
public partial class Survey
{
public Survey()
{
this.Clients = new List<Client>();
}
public int Id { get; set; }
public string Name { get; set; }
public int? ClientId { get; set; }
public virtual ICollection<Client> Clients { get; set; }
public virtual Client Client { get; set; }
}
public class ClientMap : EntityTypeConfiguration<Client>
{
#region Constructors and Destructors
public ClientMap()
{
// Primary Key
this.HasKey(t => t.Id);
// Properties
this.Property(t => t.Name).HasMaxLength(50);
// Table & Column Mappings
this.ToTable("Client");
this.Property(t => t.Id).HasColumnName("Id");
this.Property(t => t.Name).HasColumnName("Name");
this.Property(t => t.DefaultSurveyId).HasColumnName("DefaultSurveyId");
// Relationships
this.HasOptional(t => t.DefaultSurvey)
.WithMany(t => t.Clients).HasForeignKey(d => d.DefaultSurveyId);
}
#endregion
}
public class SurveyMap : EntityTypeConfiguration<Survey>
{
#region Constructors and Destructors
public SurveyMap()
{
// Primary Key
this.HasKey(t => t.Id);
// Properties
this.Property(t => t.Name).HasMaxLength(50);
// Table & Column Mappings
this.ToTable("Survey");
this.Property(t => t.Id).HasColumnName("Id");
this.Property(t => t.Name).HasColumnName("Name");
this.Property(t => t.ClientId).HasColumnName("ClientId");
// Relationships
this.HasOptional(t => t.Client)
.WithMany(t => t.Surveys).HasForeignKey(d => d.ClientId);
}
#endregion
}