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Show HN: Mapperly – A .NET source generator for object to object mappings

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Re: Show HN: Mapperly – A .NET source generator for object to object mappings

#3

Post by royjacobs »

I've never really understood the use case for these mapping generators. Every time I've seen them used (MapStruct in Java, AutoMapper in C#) the mapping configuration eventually ends up being so complex that just manually writing out the mapping would've been just as simple and arguably simpler to understand.

Re: Show HN: Mapperly – A .NET source generator for object to object mappings

#4

Post by kemiller2002 »

royjacobs wrote: post #3

I've never really understood the use case for these mapping generators. Every time I've seen them used (MapStruct in Java, AutoMapper in C#) the mapping configuration eventually ends up being so complex that just manually writing out the mapping would've been just as simple and arguably simpler to understand.

We ran into a problem where AutoMapper changed it's approach between versions for a way we were using it. We then got to spend the next few weeks updating our code because of it. I'm pretty sure that all the time we "saved" by using it was lost.

Re: Show HN: Mapperly – A .NET source generator for object to object mappings

#5

Post by latonz »

Idiot_in_Vain wrote: post #2

What are the advantages over AutoMapper?

Automapper generates all mappings at runtime with reflection. Mapperly in contrast uses roslyn based source generators and generates all mapping code at compile time. This leads to improved runtime performance with less allocations [1]. Since no reflection is used at runtime, the generated code is completely trimming save and AOT friendly.

[1] https://github.com/mjebrahimi/Benchmark.netCoreMappers

Re: Show HN: Mapperly – A .NET source generator for object to object mappings

#6

Post by orra »

latonz wrote: post #5
Idiot_in_Vain wrote: post #2

What are the advantages over AutoMapper?

Automapper generates all mappings at runtime with reflection. Mapperly in contrast uses roslyn based source generators and generates all mapping code at compile time. This leads to improved runtime performance with less allocations [1]. Since no reflection is used at runtime, the generated code is completely trimming save and AOT friendly. [1] https://github.com/mjebrahimi/Benchmark.netCoreMappers

Those are pretty compelling advantages. Thanks for sharing.

Re: Show HN: Mapperly – A .NET source generator for object to object mappings

#7

Post by orra »

royjacobs wrote: post #3

I've never really understood the use case for these mapping generators. Every time I've seen them used (MapStruct in Java, AutoMapper in C#) the mapping configuration eventually ends up being so complex that just manually writing out the mapping would've been just as simple and arguably simpler to understand.

I've used Automapper a few times, in Enterprise software which takes separate layers to a dogmatic extreme. Automapper always felt like a code smell: if the layers are so trivially mappable, should they really be different layers? Alternatively, isn't automapping a violation of the philosophy of separation of layers?

All that said, given these mappers exist, the fact this Mapperly does ahead of time code generation is an advantage over the previous generation of generators which had to use reflection.

Re: Show HN: Mapperly – A .NET source generator for object to object mappings

#9

Post by Yuioup »

royjacobs wrote: post #3

I've never really understood the use case for these mapping generators. Every time I've seen them used (MapStruct in Java, AutoMapper in C#) the mapping configuration eventually ends up being so complex that just manually writing out the mapping would've been just as simple and arguably simpler to understand.

I banned Automapper from my company.
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