Prevent AutoMapper Projections From Forcing Related Data Loading - entity-framework

Question

Is there a way to configure AutoMapper to adhere to the .Include style loading instructions for Entity Framework?
I've disabled lazy loading for my context, and I want to conditionally load related data for particular entities. Ideally, I'd like to do this by using an include syntax. Something like:
if(loadAddreses)
{
query = query.Include(e => e.Addresses);
}
if(loadEmails)
{
query = query.Include(e => e.Emails);
}
The problem is, AutoMapper is seeing that the model I'm projecting to includes Addresses and E-mails, and is generating SQL that loads all that data regardless of what I've asked EF to include. In other words:
var model = query.Project.To<MyModel>();
If MyModel has an Addresses collection, it will load addresses, regardless of my Include statements.
Short of changing my model so that I have one that doesn't have an Addresses or Emails property, is there a way to fix this? I suppose I could change my mapping, but mappings are usually static and don't change after they're initially created.

Answer 1

This was kind of tricky to tease out, but see how this works for you. Note that I'm using version 3.3.0-ci1027 of AutoMapper (at the time of writing this was a pre-release).
Assume my data model looks like this:
public class Address
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int AddressId { get; set; }
public string Text { get; set; }
}
public class Email
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int EmailId { get; set; }
public string Text { get; set; }
}
public class User
{
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
public virtual ICollection<Address> Addresses { get; set; }
public virtual ICollection<Email> Emails { get; set; }
public User()
{
this.Addresses = new List<Address>();
this.Emails = new List<Email>();
}
}
My view models are not specified but they just contain the same properties as the entities.
My mapping from User to UserViewModel looks like this:
Mapper.CreateMap<User, UserViewModel>()
.ForMember(x => x.Emails, opt => opt.ExplicitExpansion())
.ForMember(x => x.Addresses, opt => opt.ExplicitExpansion());
And my projection looks like this:
var viewModels = context.Set<User>().Project()
.To<UserViewModel>(new { }, u => u.Emails).ToList();
With that mapping and projection, only the Emails collection is loaded. The important parts to this are the opt => opt.ExplicitExpansion() call in the mapping - which prevents a navigation property being followed unless explicitly expanded during projection, and the overloaded To method. This overload allows you to specify parameters (which I've left as an empty object), and the members you wish to expand (in this case just the Emails).
The one thing I'm not sure of at this stage is the precise mechanism to extract the details from the Include statements so you can in turn pass them into the To method, but hopefully this gives you something to work with.