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InvalidCastException when using polymorphic mapping with required properties #906
Description
Seem to have run into somewhat of an issue with v10 of Mapster vs the latest v7 release. Potentially related to the support for required properties?
TypeAdapterConfig.Compile() throws an InvalidCastException when all three of the following conditions are met:
- Polymorphic mapping using
.Include<TDerived, TDerivedDest>() - Abstract destination type
requiredproperties on the destination type
Removing any one of these conditions either resolves the issue or produces a different (expected) error.
Mapster versions: 10.0.0-10.0.7-pre02
Target framework: net8.0
Minimal Reproduction
using Mapster;
var config = TypeAdapterConfig.GlobalSettings;
config.NewConfig<ConcreteSource, ConcreteDestination>();
config.NewConfig<AbstractSource, AbstractDestination>()
.Include<ConcreteSource, ConcreteDestination>();
config.Compile(); // Throws InvalidCastException
// --- Source types ---
public abstract class AbstractSource
{
public abstract string Name { get; }
}
public class ConcreteSource : AbstractSource
{
public override string Name => "Test";
}
// --- Destination types ---
public abstract class AbstractDestination
{
public required string Name { get; set; }
}
public class ConcreteDestination : AbstractDestination;Stack Trace
Mapster.CompileException: Error while compiling
source=AbstractSource
destination=AbstractDestination
type=Map
---> System.InvalidCastException: Unable to cast object of type 'System.Linq.Expressions.UnaryExpression' to type 'System.Linq.Expressions.NewExpression'.
at Mapster.Adapters.ClassAdapter.CreateInlineExpression(Expression source, CompileArgument arg, Boolean IsRequiredOnly)
at Mapster.Adapters.BaseAdapter.CreateBlockExpressionBody(Expression source, Expression destination, CompileArgument arg)
at Mapster.Adapters.BaseAdapter.CreateExpressionBody(Expression source, Expression destination, CompileArgument arg)
at Mapster.Adapters.BaseAdapter.CreateAdaptFunc(CompileArgument arg)
at Mapster.TypeAdapterConfig.CreateMapExpression(CompileArgument arg)
--- End of inner exception stack trace ---
at Mapster.TypeAdapterConfig.CreateMapExpression(CompileArgument arg)
at Mapster.TypeAdapterConfig.CreateMapExpression(TypeTuple tuple, MapType mapType)
at Mapster.TypeAdapterConfig.Compile(Boolean failFast)Workaround
Remove the required keyword from destination properties and use default initialisers instead.
Activity
DocSvartz commentedon Mar 31, 2026
Hi @DS-DanielW. Yes, it does have to do with that. Thanks!
fix: MapsterMapper#906 - InvalidCastException when using polymorphic …