唯一索引属性的实体框架FK

Question

I`d like to add foreign key on unique not null attribute in second table. Here how it look like:

 public class T_AlarmTresholds
    {
        [Key]
        public int Id { get; set; }
              ....
              ....                
        public Guid MeasurementGuid { get; set; }

        [ForeignKey("MeasurementGuid")]
        public virtual T_Measurements Measurement { get; set; }
    }


 public partial class T_Measurements
    {
        public int Id { get; set; }
        [Index("UC_Guid", IsUnique = true)]
        public Guid GUID { get; set; }
    }

Here is model builder:

modelBuilder.Entity<T_Measurements>()
                .HasMany(x => x.T_AlarmTresholds)
                .WithRequired(x => x.Measurement)
                .HasForeignKey(x => x.MeasurementGuid);

Entity framework throws error while SQL Server accept this solution. Here is error in Visual Studio while debugging:

{"One or more validation errors were detected during model generation:\\r\\n\\r\\nT_Measurements_T_AlarmTresholds_Source_T_Measurements_T_AlarmTresholds_Target: : The types of all properties in the Dependent Role of a referential constraint must be the same as the corresponding property types in the Principal Role. The type of property 'MeasurementGuid' on entity 'T_AlarmTresholds' does not match the type of property 'ID' on entity 'T_Measurements' in the referential constraint 'T_Measurements_T_AlarmTresholds'.\\r\\n"}

Answer 1

You don't put the foreign key on the virtual object itself you need to create a new property in T_AlarmTresholds:

public int T_MeasurementsId{get; set;}

to act as the foreign key. The dependency property (the virtual one) will then link up automatically. You also need to remove the ForiegnKey attribute from the virtual property.

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Just spotted that your code doesn't use the Id column as the primary key but instead uses the Guid, so you'll instead want to add the foreign key attribute to the MeasurementGuid property.