AutoMapper: Missing type map configuration

While trying out AutoMapper I stumbled on this generic error:

Message: AutoMapper.AutoMapperMappingException : Missing type map configuration or unsupported mapping.

Below is the initial Stack Overflow question I wrote, after struggling for at least 25 minutes with this problem. The solution however was shamefully simple: if you call Mapper.Initialize twice, the latter will overwrite the first.

// WRONG!

// AutoMapper.Mapper.Initialize(cfg => cfg.CreateMap());

// Do this instead!

AutoMapper.Mapper.Initialize(cfg => {

cfg.CreateMap();

});

// Or use Profiles: https://github.com/AutoMapper/AutoMapper/wiki/Configuration

Full Description

So why am I writing an entire post about this? Simple: to ingrain this solution into my brain, may I never make the same mistake again.

Basically, I was trying to understand a more specific version of this generic question on AutoMapperMappingException, getting the same kind of error message:

Message: AutoMapper.AutoMapperMappingException : Missing type map configuration or unsupported mapping.

Here’s a way to repro my scenario:

Using VS2017, create new “xUnit Test Project (.NET Core)” project (gets xUnit 2.2 for me, targets .NETCoreApp 1.1)
Run `Install-Package AutoMapper -Version 6.0.2

Add the following code

public class FooEntity { string Foo { get; set; } }

public class FooViewModel { string Foo { get; set; } }

public class BarEntity { string Bar { get; set; } }

public class BarViewModel { string Bar { get; set; } }

public class UnitTest1

{

[Fact]

public void Test1()

{

AutoMapper.Mapper.Initialize(cfg => cfg.CreateMap());

AutoMapper.Mapper.Initialize(cfg => cfg.CreateMap()); // Culprit!

var entity = new FooEntity();

var model = AutoMapper.Mapper.Map(entity);

Assert.NotNull(model);

}

Build
Run all tests

Expected result: green test.
Actual result: error message:

Message: AutoMapper.AutoMapperMappingException : Missing type map configuration or unsupported mapping.

Mapping types:
FooEntity -> FooViewModel
XUnitTestProject3.FooEntity -> XUnitTestProject3.FooViewModel

If I uncomment the line marked as “culprit” the test turns green. I fail to see why.

I also placed a Mapper.Configuration.AssertConfigurationIsValid() call right before the Map call but that will run without error.

As far as I can tell, the other question, specifically its top answer talks about forgetting the initialization, but that’s explicitly there. I’ve also looked through the other answers but none of them helped me.

Another top question’s answer to this same problem tells me to add ReverseMap(), but that’s not applicable for my scenario.

Solution

Only after writing the entire above question on Stack Overflow, specifically while perfecting the minimal repro, did I realize what was causing the error: the line marked as “Culprit!”. Then, buried deep in Google’s search results (okay, okay: on page 2; but who looks on page 2 of search results?!) I find this answer that has the solution. Multiple initializations should be done like this:

AutoMapper.Mapper.Initialize(cfg => {

cfg.CreateMap();

});

I guess that teaches me for disregarding the advice to use Profiles for proper AutoMapper configuration.