MapsterMapper/Mapster

Can't use conditional mapping with different types of source field

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#673 opened on Feb 1, 2024

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Description

For example there are 2 classes:

public class Source
{
    public int? IntValue { get; set; }
    public string StringValue { get; set; } = "Some Value";
}

public class Destination
{
    public string Mapped { get; set; } = string.Empty;
}

The task is put in Mapped string representation of IntValue if it's not null, otherwise use StringValue. I assume configuration should look like (according to Mapster docs):

TypeAdapterConfig.GlobalSettings
    .NewConfig<Source, Destination>()
    .Map(dest => dest.Mapped, src => src.IntValue, src => src.IntValue.HasValue)
    .Map(dest => dest.Mapped, src => src.StringValue);

But it gives runtime exception:

Mapster.CompileException: Error while compiling
source=Source
destination=Destination
type=Map
 ---> System.InvalidOperationException: No coercion operator is defined between types 'System.Nullable`1[System.Int32]' and 'System.String'.

Is it intended behavior or it's a bug? How to perform conditional mapping in given case Mapster way, without slapping .AfterMapping() and do it with custom code?

Contributor guide

Research direction
Inspect the conditional mapping implementation in Mapster's source code to understand how it handles different source field types. Look for where the error 'No coercion operator is defined' occurs and determine if it's a bug or intended behavior. Consider testing with explicit type conversion or using a custom resolver.
Tech stack
csharp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#Mapster
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75