Nest automap fields of child classes

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1

Hello,

we are currently wrestling with the following problem in our C# code with NEST.

Say we have a parent object with that contains a property that refers to an abstract class:
(simplified example)

class ParentObject { public AbstractSource Src { get; set; } }
abstract class AbstractSource { public string SrcField {get; set; }}
class Source1 : AbstractSource { public string Source1Field {get; set; }}
class Source2 : AbstractSource { public string Source2Field {get; set; }}

We are creating our index using Nest with a mapping using AutoMap.
...Map(m => m.AutoMap())

However, Automap only creates a mapping for the fields on AbstractSource and not on it's children (Source1 and Source2). Is there a way to solve this?

We tried adding extra mappings by:
.AutoMap()
.Properties(p =>
p.Object(o => o.Name("src").AutoMap())
p.Object(o => o.Name("src").AutoMap())
but this does not work (only the mapping of 1 of the 2 sources appears).

Of course our problem can be partly solved by

  • declaring every property that is on a child manually using .Properties()
  • using DynamicMappings, and predefining mappings for field types

However, we would prefer not to do this as it is very verbose and not very practical on a large project (a lot of inside knowledge about mappings and the nest syntax is required) and it is a lot cleaner and easier to have AutoMap look at the mapping attributes on our poco's.

2

This is a C# language constraint; since the Src property is of type AbstractSource, automapping will only ever pick up properties declared on that type.

You could use the PropertyWalker that walks C# type properties to map these in an implementation. Something like

public class Promise<TValue> : IPromise<TValue> where TValue : class
{
    public Promise(TValue value)
    {
        Value = value;
    }
    
    public TValue Value { get; } 
}

public class MultiPropertyWalker
{
    Type[] _types;
    
    public MultiPropertyWalker(params Type[] types)
    {      
        _types = types;
    }
    
    public IProperties GetProperties()
    {
        var allProperties = new Properties();
        
        foreach (var type in _types)
        {
            var walker = new PropertyWalker(type, null);
            var properties = walker.GetProperties();

            foreach (var property in properties)
                allProperties[property.Key] = property.Value;
        }
        
        return allProperties;
    }
}

then use it with

client.CreateIndex("index", c=> c
	.Mappings(m => m
		.Map<ParentObject>(mm => mm
			.AutoMap()
			.Properties(p => p
				.Object<AbstractSource>(o => o
                    .Name(n => n.Src)
                    .AutoMap()
                    .Properties(op => new Promise<IProperties>(
                        new MultiPropertyWalker(typeof(AbstractSource), typeof(Source1), typeof(Source2)).GetProperties())
                    )
                )
			)
		)
	)
);

which produces

{
  "mappings": {
    "parentobject": {
      "properties": {
        "src": {
          "type": "object",
          "properties": {
            "srcField": {
              "fields": {
                "keyword": {
                  "ignore_above": 256,
                  "type": "keyword"
                }
              },
              "type": "text"
            },
            "source1Field": {
              "fields": {
                "keyword": {
                  "ignore_above": 256,
                  "type": "keyword"
                }
              },
              "type": "text"
            },
            "source2Field": {
              "fields": {
                "keyword": {
                  "ignore_above": 256,
                  "type": "keyword"
                }
              },
              "type": "text"
            }
          }
        }
      }
    }
  }
}

Bear in mind that for any derived types that implement a property with the same name but different type, the last one mapped will supercede any previously mapped properties.

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