Ok, first of all, I’m definitely going to write about something other than mapper performance soon. This is my third blog on the subject and I want to talk a bit about some unique AgileMapper features! But we’ve got new versions of AgileMapper, AutoMapper and Mapster - the latter including a fix for the bug I found writing my last blog on this subject - and some nuances to talk about.

As this is my third update on this subject - and as it’s Christmas time - here’s the mappers and tests we’re talking about, so you don’t have to visit the previous blogs. You’re welcome! :)

The Mappers

The mappers I’ll be comparing are:


My mapper project, now on version 0.9. AgileMapper focuses on ease of use, flexibility and transparency.


You all already know about AutoMapper - it’s AutoMapper! I’m now testing version 5.2.0, as well as version 4.2.1, as requested by a reader.


ExpressMapper is a ‘lightweight’ mapper, first written as a faster alternative to the AutoMapper 4.x.x series.


Mapster is another ‘lightweight’ mapper, written to be “kind of like AutoMapper, just simpler and way, way faster” (quoted from their NuGet page). Now on version 2.6.1, and the author has optimised its use in my tests.


ValueInjecter is written for flexibility, and supports unflattening as well as flattening.

The Tests

The performance test project is a console project based on the AutoMapper benchmark which performs each of the following, for each mapper, 1 million times:

  • Constructor mapping - creating a POCO with a single constructor parameter from a POCO with a matching property

  • Complex mapping - deep cloning a Foo POCO with various kinds of value type properties, multiply-recursive Foo, List<Foo> and Foo[] properties, and IEnumerable<int> and int[] properties

  • Flattening - mapping from a POCO with nested POCO properties to a POCO with all value type (and string) properties

  • Unflattening - mapping from a POCO with all value type (and string) properties to an object with nested POCO properties - only AgileMapper and ValueInjecter support this at the time of writing

  • Deep mapping - mapping a POCO with nested POCO and POCO collection properties onto a differently-typed POCO with corresponding properties

The Nuances

I had a pull request to add the AllowPartiallyTrustedCallers attribute to the test project. As explained in this StackOverflow question, Funcs compiled from Expression trees are hosted in dynamically-created, partially-trusted assemblies; subsequent executions of these Funcs incur a security overhead. Applying AllowPartiallyTrustedCallers to the calling assembly causes part of the security checks to be skipped, which speeds things up.

As you’d expect, that’s not the whole story, though - assemblies marked with AllowPartiallyTrustedCallers can only call assemblies with compatible security settings. Applying it to the test project means it can’t call ExpressMapper, Mapster, ValueInjecter or AutoMapper 4.2.1. So you can’t just go around slapping AllowPartiallyTrustedCallers on everything then kick back to think what you’ll do with all the execution time you’ve saved :)

Results Time!

Here’s the updated results - as mentioned, the numbers are the total seconds required to perform 1 million iterations of each test. ‘w/ APTC’ is the time with AllowPartiallyTrustedCallers applied.

  Constructor Complex Flattening Unflattening Deep
Manual 0.00880 1.56607 0.05303 0.05021 0.47373
AgileMapper 0.9 0.15377 3.49969 0.33809 0.50427 1.09299
AgileMapper 0.9 w/ APTC 0.13513 2.00515 0.21154 0.38073 0.57013
AutoMapper 5.2 0.16253 7.60686 0.38347 - 0.97259
AutoMapper 5.2 w/ APTC 0.15512 6.22497 0.23118 - 0.57299
AutoMapper 4.2.1 1.16314 118.58244 3.47239 - 23.18986
ExpressMapper 1.8.3 0.21227 14.15144 0.51291 - 6.25267
Mapster 2.6.1 0.03146 3.23346 0.20822 - 0.73005
ValueInjecter 0.44900 98.57722 12.67822 13.59581 27.74575

Points to Note

  • Mapster is still the fastest at churning out simple mappings - look at that constructor test time!

  • AgileMapper with AllowPartiallyTrustedCallers applied is the fastest at performing non-simple mappings - quite pleased with that! :)

  • As mentioned previously, the performance improvements in AutoMapper 5 were huge

Ok, that’s it - no more Mapper performance talk… for a while. Stay tuned for some blogs on some unique things AgileMapper can do for you :)