Multiple 0..1 relations to same table Entity Framework code first

Question

I am trying to get multiple "units" to have a set of "UnitInfo" assigned but I get the following message from EF when using code first:

One or more validation errors were detected during model generation: Unit_UnitInfo_Source: : Multiplicity is not valid in Role 'Unit_UnitInfo_Source' in relationship 'Unit_UnitInfo'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be ''. SubUnit_UnitInfo_Source: : Multiplicity is not valid in Role 'SubUnit_UnitInfo_Source' in relationship 'SubUnit_UnitInfo'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be ''.

The classes I use looks like this:

public class Unit
{
    public int UnitId { get; set; }
    public string Name { get; set; }
    public List<SubUnit> SubUnits { get; set; }

    [ForeignKey("UnitInfoId")]
    public UnitInfo UnitInfo { get; set; }
}

public class SubUnit
{
    public int SubUnitId { get; set; }
    public string Name { get; set; }

    [ForeignKey("UnitInfoId")]
    public UnitInfo UnitInfo { get; set; }
}

public class UnitInfo
{
    public int UnitInfoId { get; set; }
    public string Function { get; set; }
    public string Location { get; set; }
}

Im sure that it is a simple mistake, I just cant figure it out.

What am I doing wrong?

You are free to mark my solution as answer if it helped solving your problem, or do not hesitate to ask more questions about it. — Daniel Leiszen

Daniel Leiszen Daniel Leiszen · Accepted Answer · 2016-12-06T11:20:59

The [ForeignKey()] attribute should refer to either the foreign key, or the navigation property in the same class. So, the UnitInfoId should be a member of the class where you specify the navigation property and the [ForeignKey()] attribute.

The navigation properties should be virtual in order to allow EF to create proxy classes for lazy loading. If you do not use fluent api, you should specify the [Key] attribute for the primary keys. Furthermore, the reference collections should be declared as virtual ICollection members. The architecture you need can be declared as follows:

public class Unit
{
    public Unit()
    {
        SubUnits = new HashSet<SubUnit>();
    }

    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int UnitId { get; set; }
    public string Name { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<SubUnit> SubUnits { get; set; }

    public int UnitInfoId { get; set; }

    [ForeignKey("UnitInfoId")]
    public virtual UnitInfo UnitInfo { get; set; }
}

public class SubUnit
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int SubUnitId { get; set; }
    public int UnitId { get; set; }
    public string Name { get; set; }

    [ForeignKey("UnitId")]
    public virtual Unit ParentUnit { get; set; }

    public int UnitInfoId { get; set; }
    [ForeignKey("UnitInfoId")]
    public UnitInfo UnitInfo { get; set; }
}

public class UnitInfo
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int UnitInfoId { get; set; }
    public string Function { get; set; }
    public string Location { get; set; }
}

However, I would recommend using inheritance, since Unit and SubUnit share the same structure. You can read more about EF code first HERE

Multiple 0..1 relations to same table Entity Framework code first

1 Answers