How to configure AutoMapper using JsonProperty attribute

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How would I need to configure AutoMapper to be able to convert a DataTable containing columns "C" and "D" to a list of MyClass by using the JsonProperty attribute for mapping?

public class MyClass
{
     [JsonProperty("C")]
     public string A { get; set; }
     [JsonProperty("D")]
     public string B { get; set; }
}
automapper json.net json c#
1 Answers

Using metadata from Json.NET's own contract resolver you can configure a name mapping from an IDataRecord to properties of your type MyClass. Having done that, you can map from any IDataReader including the one returned by DataTable.CreateDataReader() to a list of instances of your type.

First add the following extension method:

public static class AutomapperJsonExtensions
{
    static readonly IContractResolver defaultResolver = new JsonSerializer().ContractResolver;

    public static void CreateJsonDataReaderMap<TDestination>(this IMapperConfigurationExpression cfg, IContractResolver resolver = null)
    {
        resolver = resolver ?? defaultResolver;
        var contract = resolver.ResolveContract(typeof(TDestination)) as JsonObjectContract ?? throw new ArgumentException(string.Format("{0} is not a JSON object.", typeof(TDestination)));

        var map = cfg.CreateMap<IDataRecord, TDestination>();

        foreach (var p in contract.Properties.Where(p => !p.Ignored && p.Writable))
        {
            // Map PropertyName in reader to UnderlyingName in TDestination
            map.ForMember(p.UnderlyingName, opt => opt.MapFrom(r => r[p.PropertyName]));
        }
    }
}

Now you can configure a MapperConfiguration and map your table to a List<MyClass> as follows:

var config = new MapperConfiguration(cfg =>
{
    cfg.CreateJsonDataReaderMap<MyClass>();
});
var mapper = config.CreateMapper();
using var reader = table.CreateDataReader();
var result = mapper.Map<List<MyClass>>(reader);

Notes:

  • Error handling for properties present in the table but not in the class, or vice versa, has not been implemented, but presumably could be.

  • If your table was created using camel-cased column names you can pass an instance of CamelCasePropertyNamesContractResolver as the second argument to CreateJsonDataReaderMap() and names should map correctly.

Demo fiddle here which uses AutoMapper version 9.

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