使用 EF Core 在通用存储库中包含使用反射的所有导航属性

Question

I'm working on creating a generic repository for an EF Core project to avoid having to write CRUD for all models. A major roadblock I've hit is navigation properties not being loaded since Core doesn't yet support lazy loading and the generic class obviously can't define .Include statements for class specific properties.

I'm trying to do something like this for my Get method to include all the properties dynamically:

public virtual T Get(Guid itemId, bool eager = false)
        {
            IQueryable<T> querySet = _context.Set<T>();

            if (eager)
            {
                foreach (PropertyInfo p in typeof(T).GetProperties())
                {
                    querySet = querySet.Include(p.Name);
                } 
            }

            return querySet.SingleOrDefault(i => i.EntityId == itemId);
        }

But it throws an error when including properties that are not navigation properties.

I found this answer which is about the same thing but its for EF 5 and involves methods that are not present in EF core:

EF5 How to get list of navigation properties for a domain object

Is it possible to accomplish the same thing in EF Core?

Answer 1

Working with metadata in EF Core is much easier than in previous EF versions. The DbContext class provides Model property which provides access to

The metadata about the shape of entities, the relationships between them, and how they map to the database.

The code which does what you ask could be like this:

public virtual IQueryable<T> Query(bool eager = false)
{
    var query = _context.Set<T>().AsQueryable();
    if (eager)
    {
        var navigations = _context.Model.FindEntityType(typeof(T))
            .GetDerivedTypesInclusive()
            .SelectMany(type => type.GetNavigations())
            .Distinct();

        foreach (var property in navigations)
            query = query.Include(property.Name);
    }
    return query;
}

public virtual T Get(Guid itemId, bool eager = false)
{
    return Query(eager).SingleOrDefault(i => i.EntityId == itemId);
}

Please note that although this does what you asked for, it's quite limited generic approach since it eager loads only the direct navigation properties of the entity, ie does not handle loading nested navigation properties with ThenInclude .

Answer 2

    private List<PropertyInfo> GetNavigationProperties<T>(GesFormaContext _gesFormaContext)
    {
        List<PropertyInfo> propertyInfos = new List<PropertyInfo>();
        _gesFormaContext.Model.GetEntityTypes().Select(x => x.GetNavigations()).ToList().ForEach(entityTypes =>
        {
            entityTypes.ToList().ForEach(property =>
            {
                propertyInfos.AddRange(typeof(T).GetProperties().Where(x => x.PropertyType == property.PropertyInfo.PropertyType).ToList());
            });

        });


        return propertyInfos;
    }