Entity Framework Core - Lazy Loading

c# entity-framework-core

Question

Bowing to my Visual Studios request, I started my latest project using Entity Framework Core (1.0.1)

So writing my database models as I always have using the 'virtual' specifier to enable lazy loading for a List. Though when loading the parent table it appears that the child list never loads.

Parent Model

public class Events
{
    [Key]

    public int EventID { get; set; }
    public string EventName { get; set; }
    public virtual List<EventInclusions> EventInclusions { get; set; }
}

Child Model

public class EventInclusions
{
    [Key]
    public int EventIncSubID { get; set; }
    public string InclusionName { get; set; }
    public string InclusionDesc { get; set; }
    public Boolean InclusionActive { get; set; }

}

Adding new records to these tables seems to work as I am used to where I can nest the EventInclusions records as a List inside the Events record.

Though when I query this table

_context.Events.Where(e => e.EventName == "Test")

The Issue

EventInclusions will return a null value regardless of the data behind the scenes.

After reading a bit I am getting the feeling this is a change between EF6 which I normally use and EF Core

I could use some help in either making a blanket Lazy Loading on statement or figuring out the new format for specifying Lazy Loading.

Caz

1
36
12/27/2016 8:52:36 AM

Accepted Answer

So it appears that EF Core does not currently support lazy loading. Its coming but may be a while off.

For now if anyone else comes across this problem and is struggling. Below is a demo of using Eager loading which is what for now you have to use.

Say before you had a person object and that object contained a List of Hats in another table.

Rather than writing

var person = _context.Person.Where(p=> p.id == id).ToList();

person.Hats.Where(h=> h.id == hat).ToList();

You need to write

var person = _context.Person.Include(p=> p.Hats).Where(p=> p.id == id).ToList();

And then person.Hats.Where(h=> h.id == hat).ToList(); will work

If you have multiple Lists - Chain the Includes

var person = _context.Person.Include(p=> p.Hats).Include(p=> p.Tickets)
                            .Include(p=> p.Smiles).Where(p=> p.id == id).ToList();

I kinda get why this method is safer, that your not loading huge data sets that could slow things down. But I hope they get Lazy loading back soon!!!

Caz

35
11/22/2017 1:47:32 AM

Popular Answer

Lazy loading is now available on EF Core 2.1 and here is link to the relevant docs:

https://docs.microsoft.com/en-us/ef/core/querying/related-data#lazy-loading



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