How can I add custom logic in AutoMapper?

Question

I have the following code.
All of the fields map nicely from the source to the destination object.
However, there is one field in the destination object that I will need to compute.

For example:
DestinationObj.Status can be set depending on certain fields from the SourceObj.

If I were to write code, it would look similar to:

foreach (var rec in listData)
{
    string status;

    if (!String.IsNullOrEmpty(rec.Field1))
    {
        status = "Stage 1";
    }

    if (!String.IsNullOrEmpty(rec.Field2))
    {
        status = "Stage 2";
    }

    if (!String.IsNullOrEmpty(rec.Field3))
    {
        status = "Stage 3";
    }
}

Can I do something similar in AutoMapper?

var config = new MapperConfiguration(c =>
{
    c.CreateMap<SourceObj, DestinationObj>()
        .ForMember(x => x.Status, m => m.MapFrom([Not sure at this point]));
});

EDIT:

List<destinationObj> destinObj = new List<destinationObj>();

foreach (var rec in listSourceObject)
{
    destinationObj do = new destinationObj();
    // Manually map all of the fields...

    string status;

    if (!String.IsNullOrEmpty(rec.Field1))
    {
        do.status = "Stage 1";
    }

    if (!String.IsNullOrEmpty(rec.Field2))
    {
        do.status = "Stage 2";
    }

    if (!String.IsNullOrEmpty(rec.Field3))
    {
        do.status = "Stage 3";
    }

    destinObj.Add(do);
}

Where does `listData` come from? Where does `status` go? The method you want to apply doesn't appear to relate to your mapping at all. — krillgar, Sep 08 '16 at 13:28
It still isn't that clear. Are both objects a collection of themselves....? — krillgar, Sep 08 '16 at 13:41

score 6 · Accepted Answer · edited May 11 '22 at 17:02

The easiest way to do this is to move your method into your mapper class. You can then access that method within your .MapFrom().

var config = new MapperConfiguration(c =>
{
    c.CreateMap<SourceObj, DestinationObj>()
        .ForMember(dest => dest.Status, opt => opt.MapFrom(src => MapStatus(src)));

});

private string MapStatus(SourceObject source)
{
    // Whatever that foreach loop actually does.
}

For more info, see Custom Value Resolvers

score 3 · Answer 2 · edited May 23 '17 at 11:46

3

Suggested solutions with MapFrom() and workarounds for expressions are not entirely correct. MapFrom() (as AutoMapper: What is the difference between MapFrom and ResolveUsing? suggests) is smarter, so it can handle nested PropertyExpressions.

To handle regular functions for mapping values, you should use ResolveUsing(), which accepts a Func<>, so you can enter the code directly and there is no need to modify the call to be expressed as Expression<Func<>>.

edited May 23 '17 at 11:46

Community

1
1

answered Sep 08 '16 at 13:52

kiziu

1,111
1
11
15

Since [version 8](https://docs.automapper.org/en/stable/8.0-Upgrade-Guide.html#resolveusing), `ResolveUsing` has been consolidated with `MapFrom`. You now have an overload that takes a `Func<>`. – martinoss Jul 14 '22 at 11:35

How can I add custom logic in AutoMapper?

2 Answers2