Automapper and NHibernate lazy loading

Question

I am struggling with this issue:

I have a list of NHibernate objects called "Project". These objects contain a lazy - loaded list of "Branches". I am trying to pass a list of Projects to a WCF service so I am using AutoMapper to transform them to flat objects.

The problem is that even though the destination objects called "ProjectContract" does not contain a list of Branches, Automapper still invokes this collection and a lot of queries are made to the database because NHibernate fires the lazy - loading and loads the Branches collection for each project.

Here are the classes and the mapping:

    public class Project
    {
     public virtual int ID
     {
        get;
        set;
     }

     public virtual string Name { get; set; }
     public virtual string Description { get; set; }

     public virtual IList<Branch> Branches { get; set; }
    }

  [DataContract]
  public class ProjectContract
  {
    [DataMember]
    public virtual int ID
    {
        get;
        set;
    }

    [DataMember]
    public virtual string Name { get; set; }

    [DataMember]
    public virtual string Description { get; set; }
  }

  public class ProjectMappings : Profile
  {
    protected override void Configure()
    {
        Mapper.CreateMap<Project, ProjectContract>();
    }
  }

My question is: Is there a way to tell AutoMapper to not touch the "Branches" collection because I don't care about it and that is a proxy that will trigger many database calls?

I temporarily fixed this with MaxDepth(0), but there are other entities where I have collections that I want to transfer, and collections that I don't want to be touched, like this one. In that case, MaxDepth(0) will not work.

Thank you, Cosmin

gdoron · Accepted Answer · 2011-12-03 22:22:25Z

2

Yes, The AutoMapper Ignore function.

Mapper.CreateMap<Source, Destination>()
    .ForMember(dest => dest.SomeValuefff, opt => opt.Ignore());

answered Dec 3, 2011 at 22:22

gdoron

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5 Comments

noir Over a year ago

I think this only works if the property is also on the destination. In any case, even if I put the "Branches" on the destination and use the Ignore option, the collection is still accessed and the loading triggered. I am interested if there is a similar function to ignore the "source" member.

gdoron Over a year ago

@noir, "There's nothing you need to do here, AutoMapper only really cares about the destination members. It only tries to map what it finds on the destination type." taken from automapper.codeplex.com/workitem/4031

noir Over a year ago

That was what I thought as well, why bother with that collection that isn't even on the destination. But I did this simple test getting a list of projects and doing a mapping on the list to Projects Contracts. I used NhProf. First is the query that loads the projects, then for each project there is a query that loads the branches. If I look at the stack trace, it points to AutoMapper.Internal.PropertyGetter.GetValue... so I am trying to think either I am not seeing something or this is a bug.

gdoron Over a year ago

@noir, ask AutoMapper: github.com/AutoMapper/AutoMapper/issues please be kind and inform me what they answered.

noir Over a year ago

Problem solved. This is what was happening: In the ProjectContract, I had a property int BranchesCount {get;set; } that I was going to set later. I forgot AutoMapper is so smart as to deduce that I want that property mapped to Project.Branches.Count. Sorry, my bad. It took me two days to figure this out.

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