How can I recursively Include ALL navigable properties to emulate Lazy Loading

问题

To emulate Lazy Loading, I would like to have a method that recursively Include's the complete object graph via Eager Loading so that upon loading the entity, all of its related data is loaded as well.

From MSDN documentation:

To include a single reference: query.Include(e => e.Level1Reference).
To include a single collection: query.Include(e => e.Level1Collection).
To include a reference and then a reference one level down: query.Include(e => e.Level1Reference.Level2Reference).
To include a reference and then a collection one level down: query.Include(e => e.Level1Reference.Level2Collection).
To include a collection and then a reference one level down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Reference)).
To include a collection and then a collection one level down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Collection)).
To include a collection and then a reference one level down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Reference)).
To include a collection and then a collection one level down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Collection)).
To include a collection, a reference, and a reference two levels down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Reference.Level3Reference)).
To include a collection, a collection, and a reference two levels down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Collection.Select(l2 => l2.Level3Reference))).

Question:

How can I recursively Include ALL navigable properties and build this into a generic repository method so that I can get a deep object graph of an entity whenever required, regardless if new properties were added?

回答1:

Ok, this is an edited version that should meet your requirements a little better:

private static void EnumerateAllIncludesList(DbContext context, IEnumerable entities, List<object> entitiesLoaded = null)
{
    if (entitiesLoaded == null)
        entitiesLoaded = new List<object>();

    foreach (var entity in entities)
        EnumerateAllIncludesEntity(context, entity, entitiesLoaded);

}

private static void EnumerateAllIncludesEntity(DbContext context, object entity, List<object> entitiesLoaded)
{
    if (entitiesLoaded.Contains(entity))
        return;

    entitiesLoaded.Add(entity);

    Type type = entity.GetType();
    var properties = type.GetProperties();

    foreach (var propertyInfo in properties)
    {
        var propertyType = propertyInfo.PropertyType;

        bool isCollection = propertyType.GetInterfaces().Any(x => x == typeof(IEnumerable)) &&
                            !propertyType.Equals(typeof(string));

        if (isCollection)
        {
            var entry = context.Entry(entity);

            if(entry.Member(propertyInfo.Name) as DbCollectionEntry == null)
                continue;

            entry.Collection(propertyInfo.Name).Load();

            var propertyValue = propertyInfo.GetValue(entity);

            if (propertyValue == null)
                continue;

            EnumerateAllIncludesList(context, (IEnumerable)propertyValue, entitiesLoaded);
        }
        else if ((!propertyType.IsValueType && !propertyType.Equals(typeof(string))))
        {
            var entry = context.Entry(entity);

            if (entry.Member(propertyInfo.Name) as DbReferenceEntry == null)
                continue;

            entry.Reference(propertyInfo.Name).Load();

            var propertyValue = propertyInfo.GetValue(entity);

            if (propertyValue == null)
                continue;

            EnumerateAllIncludesEntity(context, propertyValue, entitiesLoaded);
        }
        else
            continue;
    }
}

You would use this like so:

using (var context = new MyContext())
{
    var result = context.People.Where(x => x.Id == 1).ToList();
    EnumerateAllIncludesList(context,result);
}

回答2:

If you use model-first or database-first, you could write some T4 template to generate what you need using edmx model. It is not easy, but possible.

来源：https://stackoverflow.com/questions/15558334/how-can-i-recursively-include-all-navigable-properties-to-emulate-lazy-loading

标签

entity-framework

entity-framework-5