How can I configure Automapper 4 to allow a null destination value - c#

I'm having some problems working out how to get Automapper 4.2.1 to allow for a type mapping where the destination value might be null depending on the source value.
Older versions of Automapper allowed an AllowNullDestination flag to be set via the Mapper configuration but I can't find the equivalent recipe for the new version and the old mechanism of configuring via the static Mapper object seems to have been obsoleted.
I have tried the following without success:
Mapper.Configuration.AllowNullDestinationValues = true;
Mapper.AllowNullDestinationValues = true;
Mapper.Initialize(c=>c.AllowNullDestinationValues=true);
Here's a simple test case demonstrating the problem. This fails on the final line with an AutoMapperMappingException since the Substitute method is returning null. I would like both mappings to succeed.
I would prefer to avoid the use of .ForMember in the solution since in the real scenario I'm trying to address, the mapping between bool and 'object' (actually a custom class) should apply across the entire object tree.
Although there are several similar questions here on StackOverflow, I haven't found one that refers to a recent version of Automapper.
Thanks in advance for any suggestions
using AutoMapper;
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace AutoMapperTest
{
[TestClass]
public class ExampleTest
{
[TestMethod]
public void NullDestinationCanBeMapped()
{
var mapper = new MapperConfiguration(configuration =>
{
configuration.CreateMap<Source, Target>();
//How should the following mapping be modified to pass the test?
configuration.CreateMap<bool, object>()
.Substitute(i => i ? null : new object());
}).CreateMapper();
var target1 = mapper.Map<Source, Target>(new Source {Member = false}); //succeeds
Assert.IsNotNull(target1.Member); //pass
var target2 = mapper.Map<Source, Target>(new Source {Member = true}); //fails to map with exception
Assert.IsNull(target2.Member); //not reached
}
}
public class Source
{
public bool Member { get; set; }
}
public class Target
{
public object Member { get; set; }
}
}

Instead of using Substitute, use ConvertUsing...
configuration.CreateMap<bool, MyClass>()
.ConvertUsing(i => i ? null : new object());

Related

How to configure NewtonsoftJson with MinimalApi in .NET 6.0

I have net6.0 project with minimal api and I would like to use NetwtonsoftJson instead of built in System.Text.Json library for serialization and deserialization.
At the moment I have this configurations for JsonOptions and that works as expected
builder.Services.Configure<JsonOptions>(options =>
{
options.SerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
options.SerializerOptions.WriteIndented = true;
options.SerializerOptions.ReferenceHandler = ReferenceHandler.IgnoreCycles;
options.SerializerOptions.Converters.Add(new JsonStringEnumConverter(JsonNamingPolicy.CamelCase));
});
If I try to change to something equivalent that uses Newtonsoft.Json.JsonSerializerSettings like below I am not getting same behavior. Instead it looks like it uses default System.Text.Json configuration.
builder.Services.Configure<JsonSerializerSettings>(options =>
{
options.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
options.Converters.Add(
new StringEnumConverter
{
NamingStrategy = new Newtonsoft.Json.Serialization.CamelCaseNamingStrategy()
});
});
In net5.0 I know I could use this
services.AddControllers().AddNewtonsoftJson((options) => //options); // OR
services.AddMvc().AddNewtonsoftJson((options) => //options);
However, if I use it like above in my net6.0 project then I am not using anymore MinimalApi ?
From my understanding Minimal APIs rely on some conventions regarding type binding. From what I can see they search for method with next signature - ValueTask<TModel?> BindAsync(HttpContext context, ParameterInfo parameter) on the type otherwise will try to use httpContext.Request.ReadFromJsonAsync which internally uses System.Text.Json and that can't be changed, so services.Add...().AddNewtonsoftJson((options) => //options); approach will not work.
To use Newtonsoft.Json you can try next (other than directly handling request via app.MapPost("/pst", (HttpContext c) => c.Request...)):
If you have control over all your classes which needs to be deserialized using it you can inherit them all from some generic base class which will have the method with needed signature (also you can use interface with implemented static method):
public class BaseModel<TModel>
{
public static async ValueTask<TModel?> BindAsync(HttpContext context, ParameterInfo parameter)
{
if (!context.Request.HasJsonContentType())
{
throw new BadHttpRequestException(
"Request content type was not a recognized JSON content type.",
StatusCodes.Status415UnsupportedMediaType);
}
using var sr = new StreamReader(context.Request.Body);
var str = await sr.ReadToEndAsync();
return JsonConvert.DeserializeObject<TModel>(str);
}
}
And usage:
class PostParams : BaseModel<PostParams>
{
[JsonProperty("prop")]
public int MyProperty { get; set; }
}
// accepts json body {"prop": 2}
app.MapPost("/pst", (PostParams po) => po.MyProperty);
Note that BaseModel<TModel> implemenation in this example is quite naive and possibly can be improved (check out HttpRequestJsonExtensions.ReadFromJsonAsync at least).
If you don't have control over the models or don't want to inherit them from some base you can look into creating wrappers:
public class Wrapper<TModel>
{
public Wrapper(TModel? value)
{
Value = value;
}
public TModel? Value { get; }
public static async ValueTask<Wrapper<TModel>?> BindAsync(HttpContext context, ParameterInfo parameter)
{
if (!context.Request.HasJsonContentType())
{
throw new BadHttpRequestException(
"Request content type was not a recognized JSON content type.",
StatusCodes.Status415UnsupportedMediaType);
}
using var sr = new StreamReader(context.Request.Body);
var str = await sr.ReadToEndAsync();
return new Wrapper<TModel>(JsonConvert.DeserializeObject<TModel>(str));
}
}
And usage changes to:
class PostParams
{
[JsonProperty("prop")]
public int MyProperty { get; set; }
}
// accepts json body {"prop": 2}
app.MapPost("/pst", (Wrapper<PostParams> po) => po.Value.MyProperty);
Some extra useful links:
MVC model binders - by David Fowler. Though I was not able to make it work for services.AddControllers().AddNewtonsoftJson((options) => //options);
ParameterBinder - similar approach by Damian Edwards

FluentAssertions Equivalency Comparison Behavior and IMemberInfo

I am using FluentAssertions (v6.2.0) to test API's that return table-like data. I want to change comparison behavior for one of the field, and tried to use method described in documentation.
orderDto.Should().BeEquivalentTo(order, options => options
.Using<DateTime>(ctx => ctx.Subject.Should().BeCloseTo(ctx.Expectation, 1.Seconds()))
.When(info => info.Name == "Date"));
The issue is that IMemberInfo class that When extension method is expecting doesn't have Name property, it has property called Path. Was Name replaced by Path and this is a typo in documentation, or do I need to import another namespace to use Name property?
From a quick look at the FluentAssertions source code, I'm seeing that the info argument is of type IObjectInfo and it has a Path property. A quick test with this code shows the Path property working as you would expect:
void Main()
{
var orderDto = new OrderDto { Date = DateTime.Now };
var order = new Order { Date = DateTime.Now };
//var order = new Order { Date = DateTime.Now.Subtract(TimeSpan.FromSeconds(2)) };
orderDto.Should().BeEquivalentTo(order, options => options
.Using<DateTime>(ctx => ctx.Subject.Should().BeCloseTo(ctx.Expectation, 1.Seconds()))
.When(info => info.Path == "Date"));
}
class OrderDto {
public DateTime Date { get; set; }
}
class Order
{
public DateTime Date { get; set; }
}
In fact, the FluentAssertions test for that code also uses path. See https://github.com/fluentassertions/fluentassertions/blob/master/Tests/FluentAssertions.Specs/Equivalency/ExtensibilityRelatedEquivalencySpecs.cs#L394
There is also an IMethodInfo interface with both Name and Path properties. However, that is used by the Include* and Exclude* methods.
So it appears to be a documentation bug.

How to xunit / Moq test an internal setter within a model in ASP.NET Core

public class Details
{
public int Id { get; internal set; }
public string Name { get; set; }
}
I have a task where a setter in a model has an internal attribute and I have tried adding stuff like
[assembly: InternalsVisibleTo("sometestrepo")]
over the model class but to no avail. I googled for a couple of hours and I can't seem to find an answer. Is it even possible to xunit test it or mock and object so that it would allow to create an object with an Id. Otherwise how else am I supposed to fully test CRUD methods that are all based around ID parameter?
The solution is to make private members that you want to test internal.
then you can add InternalsVisibleTo attribute.
[assembly: InternalsVisibleTo("sometestrepo")]
if you're using Moq,You can use something like that:-
var mockAddress = new Mock<Details>();
mockAddress.SetupGet(p => p.Id).Returns(42);
mockAddress.SetupGet(p => p.Name).Returns("Whatever you want to match");
var mockAddressRepository = new Mock<IRepository<Details>>();
var addresses = new List<Details> { mockAddress.Object };
mockAddressRepository.Setup(p => p.GetEnumerator()).Returns(addresses.GetEnumerator());
var addressToMatch = mockAddressRepository.Object.FirstOrDefault(address => address.Id == 42);
Console.WriteLine(addressToMatch.Name);
Expected Output Is:-
Whatever you want to match
One solution that might work is to use a fake.
In your Test class create a fake Details class, inheriting from Details. Then you could new up the property.
public class FakeDetails : Details
{
public new int Id { get; set; }
}
You could use the fake in your test then to set the properties.
var fakeDetails = new FakeDetails();
fakeDetails.Id = 15;
fakeDetails.Name = "Some Name";

Returning a List or IEnumerable with IHttpActionResult [duplicate]

I am working with ASP.NET MVC 5 Web Api. I want consult all my users.
I wrote api/users and I receive this:
"The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'"
In WebApiConfig, already I added these lines:
HttpConfiguration config = new HttpConfiguration();
config.Formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);
config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
But it still doesn't work.
My function for return data is this:
public IEnumerable<User> GetAll()
{
using (Database db = new Database())
{
return db.Users.ToList();
}
}
If you are working with EF, besides adding the code below on Global.asax
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings
.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
GlobalConfiguration.Configuration.Formatters
.Remove(GlobalConfiguration.Configuration.Formatters.XmlFormatter);
Dont`t forget to import
using System.Data.Entity;
Then you can return your own EF Models
Simple as that!
When it comes to returning data back to the consumer from Web Api (or any other web service for that matter), I highly recommend not passing back entities that come from a database. It is much more reliable and maintainable to use Models in which you have control of what the data looks like and not the database. That way you don't have to mess around with the formatters so much in the WebApiConfig. You can just create a UserModel that has child Models as properties and get rid of the reference loops in the return objects. That makes the serializer much happier.
Also, it isn't necessary to remove formatters or supported media types typically if you are just specifying the "Accepts" header in the request. Playing around with that stuff can sometimes make things more confusing.
Example:
public class UserModel {
public string Name {get;set;}
public string Age {get;set;}
// Other properties here that do not reference another UserModel class.
}
Given right answer is one way to go, however it is an overkill when you can fix it by one config settings.
Better to use it in the dbcontext constructor
public DbContext() // dbcontext constructor
: base("name=ConnectionStringNameFromWebConfig")
{
this.Configuration.LazyLoadingEnabled = false;
this.Configuration.ProxyCreationEnabled = false;
}
Asp.Net Web API Error: The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8'
Add this code to global.asax below on Application_Start:
Update from .Ignore to .Serialize . It must work.
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Serialize;
GlobalConfiguration.Configuration.Formatters.Remove(GlobalConfiguration.Configuration.Formatters.XmlFormatter);
public class UserController : ApiController
{
Database db = new Database();
// construction
public UserController()
{
// Add the following code
// problem will be solved
db.Configuration.ProxyCreationEnabled = false;
}
public IEnumerable<User> GetAll()
{
return db.Users.ToList();
}
}
I resolved it using this code to WebApiConfig.cs file
var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
config.Formatters.Remove(config.Formatters.XmlFormatter);
I don't like this code:
foreach(var user in db.Users)
As an alternative, one might do something like this, which worked for me:
var listOfUsers = db.Users.Select(r => new UserModel
{
userModel.FirstName = r.FirstName;
userModel.LastName = r.LastName;
});
return listOfUsers.ToList();
However, I ended up using Lucas Roselli's solution.
Update: Simplified by returning an anonymous object:
var listOfUsers = db.Users.Select(r => new
{
FirstName = r.FirstName;
LastName = r.LastName;
});
return listOfUsers.ToList();
Adding this in your Application_Start() method of Global.asax file should solve the problem
protected void Application_Start()
{
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings
.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
GlobalConfiguration.Configuration.Formatters
.Remove(GlobalConfiguration.Configuration.Formatters.XmlFormatter);
// ...
}
METHOD 2: [Not recommended]
If you are working with EntityFramework, you can disable proxy in your DbContext class constructor. NOTE: this code wll be removed if you update the model
public class MyDbContext : DbContext
{
public MyDbContext()
{
this.Configuration.ProxyCreationEnabled = false;
}
}
There's also this scenario that generate same error:
In case of the return being a List<dynamic> to web api method
Example:
public HttpResponseMessage Get()
{
var item = new List<dynamic> { new TestClass { Name = "Ale", Age = 30 } };
return Request.CreateResponse(HttpStatusCode.OK, item);
}
public class TestClass
{
public string Name { get; set; }
public int Age { get; set; }
}
So, for this scenario use the [KnownTypeAttribute] in the return class (all of them) like this:
[KnownTypeAttribute(typeof(TestClass))]
public class TestClass
{
public string Name { get; set; }
public int Age { get; set; }
}
This works for me!
My personal favorite: Just add the code below to App_Start/WebApiConfig.cs. This will return json instead of XML by default and also prevent the error you had. No need to edit Global.asax to remove XmlFormatter etc.
The 'ObjectContent`1' type failed to serialize the response body for content type 'application/xml; charset=utf-8
config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
Just put following lines in global.asax:
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
GlobalConfiguration.Configuration.Formatters.Remove(GlobalConfiguration.Configuration.Formatters.XmlFormatter);
Import
using System.Data.Entity;
Use AutoMapper...
public IEnumerable<User> GetAll()
{
using (Database db = new Database())
{
var users = AutoMapper.Mapper.DynamicMap<List<User>>(db.Users);
return users;
}
}
Use the following namespace:
using System.Web.OData;
Instead of :
using System.Web.Http.OData;
It worked for me
Add the below line
this.Configuration.ProxyCreationEnabled = false;
Two way to use ProxyCreationEnabled as false.
Add it inside of DBContext Constructor
public ProductEntities() : base("name=ProductEntities")
{
this.Configuration.ProxyCreationEnabled = false;
}
OR
Add the line inside of Get method
public IEnumerable<Brand_Details> Get()
{
using (ProductEntities obj = new ProductEntities())
{
this.Configuration.ProxyCreationEnabled = false;
return obj.Brand_Details.ToList();
}
}
Use [Serializable] for class:
Example:
[Serializable]
public class UserModel {
public string Name {get;set;}
public string Age {get;set;}
}
It worked for me!
Solution that worked for me:
Use [DataContract] for class and [DataMember] attributes for each property to serialize. This is enough to get Json result (for ex. from fiddler).
To get xml serialization write in Global.asax this code:
var xml = GlobalConfiguration.Configuration.Formatters.XmlFormatter;
xml.UseXmlSerializer = true;
Read this article, it helped me to understand serialization:
https://www.asp.net/web-api/overview/formats-and-model-binding/json-and-xml-serialization
To add to jensendp's answer:
I would pass the entity to a user created model and use the values from that entity to set the values in your newly created model. For example:
public class UserInformation {
public string Name { get; set; }
public int Age { get; set; }
public UserInformation(UserEntity user) {
this.Name = user.name;
this.Age = user.age;
}
}
Then change your return type to: IEnumerable<UserInformation>
While all these answers above are correct, one may want to check the InnerException > ExceptionMessage.
If it says something like this "The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.". This could be an issue because of default behavior of the EF.
By assigning LazyLoadingEnabled = false in your DbContext constructor will do the trick.
public class MyDbContext : DbContext
{
public MyDbContext()
{
this.Configuration.LazyLoadingEnabled = false;
}
}
For more detailed reading about EagerLoading and LazyLoading behavior of EF refer this MSDN Article.
In my case I have had similar error message:
The 'ObjectContent`1' type failed to serialize the response body for
content type 'application/xml; charset=utf-8'.
But when I dig deeper in it, the issue was:
Type 'name.SomeSubRootType'
with data contract name
'SomeSubRootType://schemas.datacontract.org/2004/07/WhatEverService'
is not expected. Consider using a DataContractResolver if you are
using DataContractSerializer or add any types not known statically to
the list of known types - for example, by using the KnownTypeAttribute
attribute or by adding them to the list of known types passed to the
serializer.
The way I solved by adding KnownType.
[KnownType(typeof(SomeSubRootType))]
public partial class SomeRootStructureType
This was solved inspired from this answer.
Reference: https://msdn.microsoft.com/en-us/library/ms730167(v=vs.100).aspx
I basically add one line which they are
entities.Configuration.ProxyCreationEnabled = false;
to UsersController.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using UserDataAccess;
namespace SBPMS.Controllers
{
public class UsersController : ApiController
{
public IEnumerable<User> Get() {
using (SBPMSystemEntities entities = new SBPMSystemEntities()) {
entities.Configuration.ProxyCreationEnabled = false;
return entities.Users.ToList();
}
}
public User Get(int id) {
using (SBPMSystemEntities entities = new SBPMSystemEntities()) {
entities.Configuration.ProxyCreationEnabled = false;
return entities.Users.FirstOrDefault(e => e.user_ID == id);
}
}
}
}
You will have to define Serializer Formatter within WebApiConfig.cs available in App_Start Folder like
Adding config.Formatters.Remove(config.Formatters.XmlFormatter);
// which will provide you data in JSON Format
Adding config.Formatters.Remove(config.Formatters.JsonFormatter);
// which will provide you data in XML Format
Another case where I received this error was when my database query returned a null value but my user/view model type was set as non-nullable. For example, changing my UserModel field from int to int? resolved.
This also happens when the Response-Type is not public!
I returned an internal class as I used Visual Studio to generate me the type.
internal class --> public class
Visual Studio 2017 or 2019 is totally unthoughtful on this, because Visual Studio itself requires the output to be in json format, while Visual Studio's default format is "XmlFormat" (config.Formatters.XmlFormatter).
Visual Studio should do this automatically instead of giving developers so much trouble.
To correct this problem, go to the WebApiConfig.cs file, and add
var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
config.Formatters.Remove(config.Formatters.XmlFormatter);
after "config.MapHttpAttributeRoutes();" in the Register(HttpConfiguration config) method. This would allow your project to produce json output.
In my case I solved recreating the database.
I made some changes in a model and launching Update-Database in Package Manager Console I got the following Error:
"The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK_dbo.Activities_dbo.Projects_ProjectId". The conflict occurred in database "TrackEmAllContext-20190530144302", table "dbo.Projects", column 'Id'."
In case: If adding code to WebApiConfig.cs or Global.asax.cs doesn't work for you:
.ToList();
Add .ToList() function.
I tried out every solution but following worked for me:
var allShops = context.shops.Where(s => s.city_id == id)**.ToList()**;
return allShops;
I hope, it helps.
in my case, it was fixed when I removed the virtual keyword before my navigation properties,
I mean the reference tables.
so I changed
public virtual MembershipType MembershipType { get; set; }
to:
public MembershipType MembershipType { get; set; }

Prevent AutoMapper to treat string as collection in LINQ ProjectTo

I've the following set of classes to map (only in one direction, from Data* to Api*):
// Top level
public class DataEntity
{
public NestedDataEntity Nested { get; set; }
// ... other primitive/complex properties
}
public class ApiEntity
{
public NestedApiEntity Nested { get; set; }
// ... other primitive/complex properties
}
// Nested level
public class NestedDataEntity
{
public string Items { get; set; }
}
public class NestedApiEntity
{
public IEnumerable<ApiSubItem> Items { get; set; }
}
public class ApiSubItem
{
// there are properties here. Not needed for the sake of example
}
Mapping is configured within a Profile as in the following bit of code:
// mapping profile
public class MyCustomProfile : Profile
{
public MyCustomProfile()
{
CreateMap<DataEntity, ApiEntity>();
CreateMap<NestedDataEntity, NestedApiEntity>();
CreateMap<string, IEnumerable<ApiSubItem>>()
.ConvertUsing<TextToSubItemsConverter>();
}
}
// type converter definition
public class TextToSubItemsConverter :
ITypeConverter<string, IEnumerable<ApiSubItem>>
{
public IEnumerable<ApiSubItem> Convert(
string dataItems, IEnumerable<ApiSubItem> apiItems, ResolutionContext context)
{
// actually, deserialize & return an ApiSubItem[]
// here just return some fixed array
return new ApiSubItem[]
{
new ApiSubItem(),
new ApiSubItem(),
new ApiSubItem(),
};
}
}
// Main
public class Program
{
public static void Main(string[] args)
{
Mapper.Initialize(cfg =>
{
cfg.AddProfile<MyCustomProfile>();
});
Mapper.AssertConfigurationIsValid();
DataEntity dataEntity = new DataEntity()
{
Nested = new NestedDataEntity()
{
Items = "Ignored text",
},
};
// This maps ok, no issues
ApiEntity apiEntity = Mapper.Map<DataEntity, ApiEntity>(dataEntity);
IQueryable<DataEntity> dataEntities = new[] { dataEntity }.AsQueryable();
// This exposes the System.Char to ApiSubItem issue
ApiEntity apiEntityProjected = dataEntities.ProjectTo<ApiEntity>().First();
}
}
Mapping configuration passes initial validation at startup, but then when an actual mapping is required I get exception:
System.InvalidOperationException: Missing map from System.Char to my.whatever.namespace.ApiSubItem. Create using Mapper.CreateMap.
If I omit completely the configuration between string and IEnumerable<ApiSubItem>, initial validation complains about the same context:
Context:
Mapping from type System.Char to my.whatever.namespace.ApiSubItem
although when added, it seems like it's not picked up by AutoMapper.
The mapping happens in a static context, through a ProjectTo<ApiEntity>() call on top of LINQ query over DbSet<DataEntity>. I've checked that converter does not require any dependency, just in case.
AutoMapper is 5.0.2, running in an MVC API web application under ASP.Net Core 1 RTM.
I've checked similar issues here on SO, but with no luck. Does anyone know how to make this type of scenario work? I guess I'm not the first one trying to (Auto)map from a string to a collection. TA
EDIT Added both failing and non-failing case to example
EDIT 2 After further search, somewhere someone suggested to ignore the field and perform mapping in AfterMap(). With this profile, exception is not thrown but resulting Items field is null:
CreateMap<DataEntity, ApiEntity>();
CreateMap<NestedDataEntity, NestedApiEntity>()
.ForMember(api => api.Items, options => options.Ignore())
.AfterMap((data, api) =>
{
api.Items = Mapper.Map<IEnumerable<ApiSubItem>>(data.Items);
});
CreateMap<string, IEnumerable<ApiSubItem>>()
.ConvertUsing<TextToSubItemsConverter>();
EDIT 3 Reworded question title to make it more specific for projection
I guess the actual answer is along the lines of "projections and converter/resolvers don't play nicely together". From AutoMapper Queryable.Extensions wiki:
Not all mapping options can be supported, as the expression generated must be interpreted by a LINQ provider. [...]
Not supported:
[...]
Before/AfterMap,
Custom resolvers,
Custom type converters
EDIT Workaround:
In this particular scenario, I've later found to be useful having an intermediate DTO entity that could grab some more fields, not needed for the final API entity but still needed for business logic.
In such DTO entity I left the string field as in DataEntity, so I could use projection and let AutoMapper/LinqToSQL grab only needed fields from DB.
Then, between DTO entity and API entity already in memory, I could apply a second mapping which also took advantage of custom converter for string ==> IEnumerable<ApiSubItem> mapping. HTH

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