Problems creating a Foreign-Key relationship on Entity Framework

Question

i'm having trouble configuring a foreign key relationship in my Entity Framework fluent Api:

Here is the head of the report:

 public class Testata {     public Testata() { Details = new List<Dettaglio>(); }     public virtual int IDTEST { get; set; }     public virtual string Value { get; set; }     public virtual int IDDETAIL { get; set; }     public virtual string IDTESTALT { get; set; }     public virtual byte[] BLOB { get; set; }      public virtual IList<Dettaglio> Details { get; set; } } 

This is the report's detail

public class Dettaglio {     public virtual int IDDETAIL { get; set; }     public virtual int IDTEST { get; set; }     public virtual string DSDETAIL { get; set; }      public virtual Testata TEST_TABLE { get; set; } } 

And this is my fluent API definition of both. Head of the report:

public TEST_TABLEMap()     {         // Primary Key         this.HasKey(t => t.IDTEST)             .Property(t => t.IDTEST)             .IsRequired()             .HasColumnType("Int")             .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity)             .HasColumnName("IDTEST");           // Table & Column Mappings         this.ToTable("TEST_TABLE");         this.Property(t => t.Value).HasColumnName("DSVALUETEST");         this.Property(t => t.IDTESTALT).HasColumnName("IDTESTALT");         this.Property(t => t.BLOB).HasColumnName("BLOB");     } 

Detail of the report:

public TEST_DETAILMap()     {         // Primary Key         this.HasKey(t => t.DSDETAIL);          // Properties         this.Property(t => t.DSDETAIL);          // Table & Column Mappings         this.ToTable("TEST_DETAIL");         this.Property(t => t.IDDETAIL).HasColumnName("IDDETAIL");         // this.Property(t => t.IDTEST).HasColumnName("IDTEST");         this.Property(t => t.DSDETAIL).HasColumnName("DSDETAIL");          // Relationships         this.HasOptional(t => t.TEST_TABLE)             .WithMany(t => t.Details)             .HasForeignKey(d => d.IDDETAIL).WillCascadeOnDelete(true);      } 

On execution i always get this error

System.Data.Entity.Edm.EdmAssociationType: : Multiplicity conflicts with the referential constraint in Role 'Dettaglio_TEST_TABLE_Target' in relationship 'Dettaglio_TEST_TABLE'. Because all of the properties in the Dependent Role are non-nullable, multiplicity of the Principal Role must be '1'.

Which, i guess, means i'm failing something at foreign key definition, but i don't really know where to look at. Any help/hint is much appreciated.

Answer 1

There is a conflict between your foreign key property in class Dettaglio...

public virtual int IDTEST { get; set; } 

...which has a non-nullable type (int) and therefore cannot be optional and your mapping...

this.HasOptional(t => t.TEST_TABLE) //... 

...where you want the relationship to be optional.

If you indeed want an optional relationship use a nullable FK property:

public virtual int? IDTEST { get; set; } 

Otherwise you must use HasRequired for a required relationship with a non-nullable FK property.