Entity Framework 6 Custom Relationship Convention


Question

I have read this documentation about convention in Entity Framework 6. But it does not contain convention for Relationship.

Suppose I have following model:

[TablePrefix("mst")]
public class Guru
{
    public int Id { get; set; }

    public int? IdKotaLahir { get; set; }

    public virtual Kota KotaLahir { get; set; }
}

I want property IdKotaLahir to be foreign key of navigation property KotaLahir. Foreign key name is "Id"+<NavigationPropertyName>. Is it possible using current version of entity framework (EF 6 alpha 3)?

Accepted Answer

Is it just one property or you need this across the board (i.e. the whole model is using a convention where foreign key names are always "Id" + NavigationPropertyName)? If you just want the foreign key for a single entity you will be better off just using the ForeignKey attribute:

public class Guru
{
    public int Id { get; set; }

    public int? IdKotaLahir { get; set; }

    [ForeignKey("IdKotaLahir")]
    public virtual Kota KotaLahir { get; set; }
}

This will work for both EF5 and EF6. In EF6 you can use custom conventions to configure foreign key properties. Here is custom convention I came up with:

public class NavigationPropertyConfigurationConvention
    : IConfigurationConvention<PropertyInfo, NavigationPropertyConfiguration>
{
    public void Apply(
        PropertyInfo propertyInfo, Func<NavigationPropertyConfiguration> configuration)
    {
        var foreignKeyProperty = 
            propertyInfo.DeclaringType.GetProperty("Id" + propertyInfo.Name);

        if (foreignKeyProperty != null && configuration().Constraint == null)
        {
            var fkConstraint = new ForeignKeyConstraintConfiguration();
            fkConstraint.AddColumn(foreignKeyProperty);

            configuration().Constraint = fkConstraint;
        }           
    }
}

I also wrote a more detailed blog post on this.


Popular Answer

In EF6, the accepted answer's convention no longer works because IConfigurationConvention is internal. The way to handle this type of scenario is by inheriting from ForeignKeyDiscoveryConvention.

public class MyForeignKeyDiscoveryConvention : ForeignKeyDiscoveryConvention
{
    protected override bool MatchDependentKeyProperty(AssociationType associationType, AssociationEndMember dependentAssociationEnd,
        EdmProperty dependentProperty, EntityType principalEntityType, EdmProperty principalKeyProperty)
    {
        string navigationPropertyName = ((System.Reflection.PropertyInfo)dependentAssociationEnd.MetadataProperties.GetValue("ClrPropertyInfo", false).Value).Name;

        // The standard foreign key property to look for is NavigationProperty_PrimaryKeyName (e.g. "TableName_Id"). 
        // Use the below line to remove that underscore.
        //return dependentProperty.Name == navigationPropertyName + principalKeyProperty.Name;

        // Use the following for the IdKotaLahir scenario
        return dependentProperty.Name == "Id" + navigationPropertyName;
    }
}




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