Entity Framework Code First: How can I determine the foreign key property used for a navigation property at runtime?

Question

I have an Entity Framework Code First DbContext with the following entities configured. In this example class Bar is a child of class Foo.

public class Foo
{
            


        

Answer 1

I was actually able to determine the foreign key properties by using the GetDependentProperties method of the NavigationProperty class.

Here is the code that I used (more or less) to get what I needed:

object[] GetForeignKeyPropertyValues(TEntity entity, Expression> navigationProperty)
{
    if (entity == null)
        return new object[] { };

    // Find the entity metadata in the object context.
    // (Assume you have access to the DbContext through the property CurrentDbContext.)
    var objectContext = (CurrentDbContext as IObjectContextAdapter).ObjectContext; 

    var metadataNamespace = ObjectContextAdapter.GetType().Namespace;

    var entityIdentity = metadataNamespace + "." + typeof(TEntity).Name; // HACK: This seems to work to retrieve the EntityType for an entity.
    var entityMetadata = objectContext.MetadataWorkspace.GetItem(entityIdentity, DataSpace.CSpace);

    // TODO: Verify that the entity metadata was found.

    // Get the navigation property metadata by parsing the name from the navigation property expression.
    var navigationPropertyName = GetPropertyName(navigationProperty);
    var navigationPropertyMetadata = entityMetadata.NavigationProperties.FirstOrDefault(np => np.Name == navigationPropertyName);

    // TODO: (JMB) Verify that the navigation property metadata was found.

    // Extract the foreign key columns from the navigation property.
    var foreignKeyPropertyMetadatas = navigationPropertyMetadata.GetDependentProperties();

    // Create property getters for each foreign key property.
    var foreignKeyPropertyGetters = foreignKeyPropertyMetadatas
        .Select(propertyMetadata => MakePropertyGetter(propertyMetadata.Name))
        .ToArray();

    // Execute the foreign key property getters to get the foreign key property values for the specified entity.
    var foreignKeyPropertyValues = foreignKeyPropertyGetters
        .Select(propertyGetter => propertyGetter(entity))
        .ToArray();

    return foreignKeyPropertyValues;
}

static string GetPropertyName(Expression> navigationProperty)
{
    var lambda = navigationProperty as LambdaExpression;
    var member = lambda.Body as MemberExpression;

    return member.Member.Name;
}

static Func MakePropertyGetter(Type entityType, string propertyName)
{
    var parameterExpression = Expression.Parameter(typeof(TEntity), "entity");
    var propertyExpression = Expression.PropertyOrField(parameterExpression, propertyName);

    var lambdaExpression = Expression.Lambda(propertyExpression, parameterExpression);
    var lambdaFunction = lambdaExpression.Compile();

    return (Func)lambdaFunction;
}