# Nest automap fields of child classes

**URL:** <https://discuss.elastic.co/t/nest-automap-fields-of-child-classes/105436>\
**Category:** Elasticsearch\
**Created:** [October 26, 2017, 1:50pm UTC](https://discuss.elastic.co/t/nest-automap-fields-of-child-classes/105436 "2017-10-26T13:50:36Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![tomboon](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/tomboon/32/26690_2.png) [@tomboon](https://discuss.elastic.co/u/tomboon)\
**Post date:** [October 26, 2017, 1:50pm UTC](https://discuss.elastic.co/t/nest-automap-fields-of-child-classes/105436/1 "2017-10-26T13:50:36Z")

</div>

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](http://o.Name)("src").AutoMap())  
p.Object(o =\> [o.Name](http://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.

---

<div class="post-metadata">

**Author:** ![forloop](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/forloop/32/9021_2.png) [@forloop](https://discuss.elastic.co/u/forloop)\
**Post date:** [November 3, 2017, 9:59am UTC](https://discuss.elastic.co/t/nest-automap-fields-of-child-classes/105436/2 "2017-11-03T09:59:53Z")

</div>

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

```auto
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

```auto
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

```json
{
  "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.

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [December 1, 2017, 9:59am UTC](https://discuss.elastic.co/t/nest-automap-fields-of-child-classes/105436/3 "2017-12-01T09:59:57Z")

</div>

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