Question

I have a set of classes I would like to map to with Automapper. However, every class has a constructor parameter. This parameter is of the same type for all members, but I do not know the value to supply until the point I want to do my mapping.

I have found the ConstructUsing method, but that requires me to specify the parameter value at time of configuration. I would prefer to do it at time of Mapping to avoid needing to create a separate MappingEngine for every instance of the parameter. I have found the Map overload that maps to an already created destination object. This is helpful, but it does not work for lists or object graphs.

Essentially, I am looking for something like this resolve method from Autofac, only applied to Automapper’s Map method.

Resolve<IFoo>( new TypedParameter( typeof( IService ), m_service) );

Answer 1

Reading through the Automapper source code, I found a workable solution which I described below.

First, you need to specify you want to use a Service Locator for construction.

IConfiguration configuration = ...;
configuration.CreateMap<Data.Entity.Address, Address>().ConstructUsingServiceLocator();

Then when calling map, you specify a specific service locator using the opts parameter

// Use DI container or manually construct function
// that provides construction using the parameter value specified in question.
// 
// This implementation is somewhat Primitive, 
// but will work if parameter specified is always the only parameter
Func<Type, object> constructingFunction =
    type => return Activator.CreateInstance( type, new object[] { s_service } );

mappingEngine.Map<Data.Entity.Address, Address>(
    source, opts: options => options.ConstructServicesUsing( constructingFunction );

The “ServiceLocator” indicated by constructingFunction above takes precedent over the function provided to IConfiguration.ConstructServicesUsing(...)