fix: ForMember with Condition but no MapFrom silently drops property

[cloud-hai-vo]

Summary

• Bug: .ForMember(d => d.Name, opt => opt.Condition(...)) without an explicit MapFrom silently dropped the property instead of mapping it by convention.
• Root cause: BuildPropertyAction returned null when SourceMemberName was null, but the destination property was already added to processedDestProps — so the convention mapping loop also skipped it, leaving zero actions for that property.
• Fix: Added a same-name convention fallback in BuildPropertyAction before the final return null. When SourceMemberName is null, EggMapper now looks up the source property by destination property name and builds the action with the full propMap (Condition/PreCondition/NullSubstitute) applied — matching AutoMapper's behavior.

Impact

Any ForMember call that configures only guards (Condition, PreCondition, NullSubstitute, or combinations) without an explicit MapFrom was silently a no-op. With this fix those properties are correctly mapped with the guards applied.

Test plan

• Condition_without_MapFrom_still_maps_by_convention — property is written when condition is true
• Condition_without_MapFrom_skips_when_false — existing destination value preserved when condition is false
• Condition_without_MapFrom_maps_into_existing_destination — regression case: Map(source, destination) path
• All 358 existing tests still pass

🤖 Generated with Claude Code

[github-actions]

📊 Benchmark Results

Generated: 2026-04-20 02:43 UTC  ·  Download full artifacts

Column guide:
Mean = average execution time  ·  Error = half of 99.9 % confidence interval  ·  StdDev = standard deviation  ·  Min / Median / Max = statistical range  ·  Ratio = vs Manual baseline (lower = closer to hand-written speed)  ·  RatioSD = ratio std dev  ·  Rank = 1 is fastest  ·  Gen0/1/2 = GC collections per 1 000 ops  ·  Allocated = managed heap per operation  ·  Alloc Ratio = allocation ratio vs baseline

🔵 Flat Mapping — 10-property object

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	15.79 ns	3.926 ns	0.215 ns	15.54 ns	15.89 ns	15.94 ns	1.00	0.02	1	0.0048	80 B	1.00
EggMapper	27.28 ns	2.485 ns	0.136 ns	27.16 ns	27.24 ns	27.43 ns	1.73	0.02	2	0.0048	80 B	1.00
AutoMapper	78.38 ns	4.104 ns	0.225 ns	78.17 ns	78.36 ns	78.62 ns	4.96	0.06	3	0.0048	80 B	1.00
Mapster	28.86 ns	2.363 ns	0.130 ns	28.74 ns	28.82 ns	29.00 ns	1.83	0.02	2	0.0048	80 B	1.00
MapperlyMap	16.48 ns	1.915 ns	0.105 ns	16.38 ns	16.47 ns	16.59 ns	1.04	0.01	1	0.0048	80 B	1.00
AgileMapper	326.11 ns	46.532 ns	2.551 ns	324.11 ns	325.23 ns	328.98 ns	20.65	0.28	4	0.0205	344 B	4.30
EggMapperGenerator	16.23 ns	1.407 ns	0.077 ns	16.15 ns	16.23 ns	16.31 ns	1.03	0.01	1	0.0048	80 B	1.00
EggMapperClassMapper	17.47 ns	2.109 ns	0.116 ns	17.36 ns	17.47 ns	17.59 ns	1.11	0.01	1	0.0048	80 B	1.00

🟡 Flattening — 2 nested objects → 8 flat properties

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	20.80 ns	9.987 ns	0.547 ns	20.19 ns	20.97 ns	21.24 ns	1.00	0.03	1	0.0048	80 B	1.00
EggMap	32.42 ns	5.601 ns	0.307 ns	32.10 ns	32.44 ns	32.71 ns	1.56	0.04	2	0.0048	80 B	1.00
AutoMapper	81.45 ns	3.177 ns	0.174 ns	81.35 ns	81.35 ns	81.66 ns	3.92	0.09	3	0.0048	80 B	1.00
Mapster	34.83 ns	1.968 ns	0.108 ns	34.73 ns	34.82 ns	34.94 ns	1.68	0.04	2	0.0048	80 B	1.00
MapperlyMap	27.12 ns	0.869 ns	0.048 ns	27.08 ns	27.11 ns	27.17 ns	1.30	0.03	2	0.0062	104 B	1.30
AgileMapper	326.94 ns	21.024 ns	1.152 ns	325.77 ns	326.97 ns	328.08 ns	15.73	0.37	4	0.0205	344 B	4.30

🟣 Deep Mapping — 2 nested address objects

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	63.73 ns	61.401 ns	3.366 ns	61.70 ns	61.88 ns	67.62 ns	1.00	0.06	1	0.0162	272 B	1.00
EggMapper	70.33 ns	4.318 ns	0.237 ns	70.17 ns	70.21 ns	70.60 ns	1.11	0.05	1	0.0162	272 B	1.00
AutoMapper	107.85 ns	0.676 ns	0.037 ns	107.82 ns	107.85 ns	107.89 ns	1.70	0.08	2	0.0162	272 B	1.00
Mapster	76.98 ns	6.577 ns	0.360 ns	76.66 ns	76.92 ns	77.37 ns	1.21	0.05	1	0.0162	272 B	1.00
MapperlyMap	54.69 ns	10.757 ns	0.590 ns	54.34 ns	54.36 ns	55.37 ns	0.86	0.04	1	0.0162	272 B	1.00
AgileMapper	359.49 ns	28.576 ns	1.566 ns	357.73 ns	359.99 ns	360.74 ns	5.65	0.25	3	0.0253	424 B	1.56

🟢 Complex Mapping — nested object + collection

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Allocated	Alloc Ratio
Manual	79.23 ns	23.402 ns	1.283 ns	77.81 ns	79.58 ns	80.31 ns	1.00	0.02	1	0.0191	320 B	1.00
EggMapper	105.71 ns	28.864 ns	1.582 ns	103.89 ns	106.46 ns	106.77 ns	1.33	0.03	1	0.0191	320 B	1.00
AutoMapper	152.29 ns	24.336 ns	1.334 ns	150.85 ns	152.54 ns	153.49 ns	1.92	0.03	2	0.0196	328 B	1.02
Mapster	99.24 ns	4.798 ns	0.263 ns	98.94 ns	99.34 ns	99.43 ns	1.25	0.02	1	0.0191	320 B	1.00
MapperlyMap	83.73 ns	17.830 ns	0.977 ns	82.67 ns	83.91 ns	84.60 ns	1.06	0.02	1	0.0191	320 B	1.00
AgileMapper	424.68 ns	27.573 ns	1.511 ns	423.32 ns	424.41 ns	426.31 ns	5.36	0.08	3	0.0315	528 B	1.65

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	2.156 μs	0.7835 μs	0.0429 μs	2.107 μs	2.175 μs	2.186 μs	1.00	0.02	1	0.5264	0.0153	8.65 KB	1.00
EggMapper	1.958 μs	0.4181 μs	0.0229 μs	1.944 μs	1.946 μs	1.985 μs	0.91	0.02	1	0.5264	0.0153	8.65 KB	1.00
AutoMapper	2.586 μs	0.5888 μs	0.0323 μs	2.549 μs	2.602 μs	2.608 μs	1.20	0.02	1	0.6065	0.0191	9.95 KB	1.15
Mapster	2.203 μs	0.4159 μs	0.0228 μs	2.188 μs	2.193 μs	2.229 μs	1.02	0.02	1	0.5264	0.0153	8.65 KB	1.00
MapperlyMap	2.169 μs	0.6345 μs	0.0348 μs	2.136 μs	2.167 μs	2.205 μs	1.01	0.02	1	0.5264	0.0153	8.65 KB	1.00
AgileMapper	2.788 μs	0.4835 μs	0.0265 μs	2.765 μs	2.782 μs	2.817 μs	1.29	0.02	1	0.5417	0.0153	8.91 KB	1.03

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	6.041 μs	3.2172 μs	0.1763 μs	5.902 μs	5.981 μs	6.239 μs	1.00	0.04	1	1.6708	0.0916	27.4 KB	1.00
EggMapper	6.502 μs	1.2983 μs	0.0712 μs	6.429 μs	6.506 μs	6.571 μs	1.08	0.03	1	1.6708	0.0916	27.4 KB	1.00
AutoMapper	7.859 μs	2.7778 μs	0.1523 μs	7.687 μs	7.912 μs	7.977 μs	1.30	0.04	1	1.7548	0.1068	28.7 KB	1.05
Mapster	6.770 μs	1.1219 μs	0.0615 μs	6.706 μs	6.776 μs	6.829 μs	1.12	0.03	1	1.6708	0.0916	27.4 KB	1.00
MapperlyMap	5.967 μs	0.2874 μs	0.0158 μs	5.949 μs	5.976 μs	5.977 μs	0.99	0.02	1	1.6785	0.0992	27.42 KB	1.00
AgileMapper	5.968 μs	0.2413 μs	0.0132 μs	5.954 μs	5.972 μs	5.979 μs	0.99	0.02	1	1.0223	0.0610	16.72 KB	0.61

🟠 Collection — 100-item List<T>

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
Manual	20.13 μs	0.929 μs	0.051 μs	20.08 μs	20.14 μs	20.18 μs	1.00	0.00	1	5.2490	1.3123	85.99 KB	1.00
EggMapper	20.07 μs	6.875 μs	0.377 μs	19.68 μs	20.10 μs	20.43 μs	1.00	0.02	1	5.2490	1.3123	85.99 KB	1.00
AutoMapper	24.58 μs	18.953 μs	1.039 μs	23.38 μs	25.07 μs	25.28 μs	1.22	0.04	1	5.7678	1.4343	94.34 KB	1.10
Mapster	20.87 μs	2.926 μs	0.160 μs	20.71 μs	20.88 μs	21.03 μs	1.04	0.01	1	5.2490	1.3123	85.99 KB	1.00
MapperlyMap	20.89 μs	3.917 μs	0.215 μs	20.65 μs	20.97 μs	21.05 μs	1.04	0.01	1	5.2490	1.2817	86.02 KB	1.00
AgileMapper	21.99 μs	1.622 μs	0.089 μs	21.89 μs	22.04 μs	22.05 μs	1.09	0.00	1	5.2795	1.3123	86.25 KB	1.00

⚪ Startup / Configuration time

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapperStartup	1,391.462 μs	1,197.0117 μs	65.6123 μs	1,324.765 μs	1,393.688 μs	1,455.933 μs	1.001	0.06	3	3.9063	1.9531	95.23 KB	1.00
AutoMapperStartup	413.470 μs	639.0771 μs	35.0300 μs	374.842 μs	422.391 μs	443.177 μs	0.298	0.03	2	5.8594	-	103.9 KB	1.09
MapsterStartup	2.488 μs	0.5001 μs	0.0274 μs	2.457 μs	2.500 μs	2.508 μs	0.002	0.00	1	0.7019	0.0267	11.51 KB	0.12

EggMapper.Benchmarks.ColdStartBenchmark-report-github

Method	Mean	Error	StdDev	Min	Median	Max	Ratio	RatioSD	Rank	Gen0	Gen1	Allocated	Alloc Ratio
EggMapper	1.304 ms	2.049 ms	0.1123 ms	1.180 ms	1.336 ms	1.398 ms	1.01	0.11	1	5.8594	-	95.58 KB	1.00
AutoMapper	4.152 ms	11.417 ms	0.6258 ms	3.578 ms	4.059 ms	4.819 ms	3.20	0.49	2	15.6250	7.8125	310.26 KB	3.25
Mapster	4.361 ms	5.436 ms	0.2980 ms	4.027 ms	4.460 ms	4.598 ms	3.36	0.33	2	46.8750	15.6250	769.01 KB	8.05

---

📝 Notes

• Each benchmark class is decorated with [MemoryDiagnoser] and [RankColumn].
• The global config (see src/EggMapper.Benchmarks/Program.cs) adds Min, Median, and Max columns.
• Manual is the hand-written baseline (ratio = 1.00). A ratio < 1 means faster than manual.
• Benchmarks run on GitHub-hosted runners — absolute times may vary between runs; focus on Ratio for comparisons.
• To reproduce locally:

  cd src/EggMapper.Benchmarks
  dotnet run --configuration Release -- --filter '*'