Using AutoMapper 8 ProjectTo on DI instance - asp.net-core

Question

I'm using the AddAutoMapper method provided in the AutoMapper.Extensions.Microsoft.DependencyInjection NuGet package to setup AutoMapper into an ASP.NET Core 2.2 web app.
It works great when mapping individual entities to models and back - I can do this with no problem:
mapper.Map<Model>(context.Set<Entity>().First());
But I can't figure out how to get ProjectTo working. I'm injecting IMapper and I've tried it both of these:
mapper.ProjectTo<Model>(context.Set<Entity>());
and
context.Set<Entity>().ProjectTo<Model>(mapper.ConfigurationProvider);
I get the same error either way:
System.ArgumentException: Static method requires null instance, non-static method requires non-null instance.
at System.Linq.Expressions.Expression.ValidateStaticOrInstanceMethod(Expression instance, MethodInfo method)
at System.Linq.Expressions.Expression.ValidateMethodAndGetParameters(Expression instance, MethodInfo method)
at System.Linq.Expressions.Expression.Call(MethodInfo method, Expression arg0)
at AutoMapper.QueryableExtensions.Impl.MemberGetterExpressionResultConverter.ExpressionResolutionResult(ExpressionResolutionResult expressionResolutionResult, MemberInfo getter) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\Impl\MemberGetterExpressionResultConverter.cs:line 24
at System.Linq.Enumerable.Aggregate[TSource,TAccumulate](IEnumerable`1 source, TAccumulate seed, Func`3 func)
at AutoMapper.QueryableExtensions.ExpressionBuilder.ResolveExpression(PropertyMap propertyMap, Type currentType, Expression instanceParameter, LetPropertyMaps letPropertyMaps) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\ExpressionBuilder.cs:line 308
at AutoMapper.QueryableExtensions.ExpressionBuilder.<>c__DisplayClass17_0.<CreateMemberBindings>g__CreateMemberBinding|0(PropertyMap propertyMap) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\ExpressionBuilder.cs:line 272
at AutoMapper.QueryableExtensions.ExpressionBuilder.CreateMemberBindings(ExpressionRequest request, TypeMap typeMap, Expression instanceParameter, IDictionary`2 typePairCount, LetPropertyMaps letPropertyMaps) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\ExpressionBuilder.cs:line 266
at AutoMapper.QueryableExtensions.ExpressionBuilder.CreateMapExpressionCore(ExpressionRequest request, Expression instanceParameter, IDictionary`2 typePairCount, TypeMap typeMap, LetPropertyMaps letPropertyMaps) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\ExpressionBuilder.cs:line 204
at AutoMapper.QueryableExtensions.ExpressionBuilder.CreateMapExpression(ExpressionRequest request, IDictionary`2 typePairCount, LetPropertyMaps letPropertyMaps) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\ExpressionBuilder.cs:line 152
at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
at System.Lazy`1.CreateValue()
at AutoMapper.QueryableExtensions.ExpressionBuilder.GetMapExpression(Type sourceType, Type destinationType, Object parameters, MemberInfo[] membersToExpand) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\ExpressionBuilder.cs:line 98
at AutoMapper.QueryableExtensions.ProjectionExpression.To[TResult](Object parameters, Expression`1[] membersToExpand) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\ProjectionExpression.cs:line 60
at AutoMapper.QueryableExtensions.Extensions.ProjectTo[TDestination](IQueryable source, IConfigurationProvider configuration, Expression`1[] membersToExpand) in C:\projects\automapper\src\AutoMapper\QueryableExtensions\Extensions.cs:line 76
I'm trying to use it as described in the docs here:
Queryable Extensions
Static and Instance API
Dependency Injection
But it looks like I'm doing something wrong with the static vs. instance setup. I'd like to use the IMapper instance I'm passing in with DI since it works fine on single maps.
What can I do to fix this error?

Answer 1

I figured out the cause of this error. Thanks Lucian Bargaoanu for the reminder about the limited supported mapping options. I was using flattening with a method prefixed with “Get” on the source type, but I don't think that works with ProjectTo. (I think that falls under the last item on the list - Any calculated property on your domain object.) And that's why LINQ was giving the error "non-static method requires non-null instance."

Answer 2

Not sure if this'll help anyone but don't forget to check that your reverse mappings also adhere to AutoMapper's supported options.
I've just spent an hour tearing my hair out on trial-and-error attempts to fix this. Finally I noticed/remembered I had ReverseMap() at the end of all my mappings, which meant a ton of source-to-destination mapping rules were violated when the mapping was reversed.