What is best approach for data inheritation in elasticsearch?

Question

I have an parent class and two child like these:

public class Parent {
    public Guid Id { get; set; }
    public string Name { get; set; }
}

public class FirstChild {
    public string IdentityCode { get; set; }
}

public class OtherChild {
    public string RegistrationCode { get; set; }
}

There is a question: Is it a good approach to store these two inherited classes in the same Index inside ElasticSearch? I see there is a _type property that is added to my docs after they are stored in DB but it has always "doc" value. I test this code to fill it but it seems it is not working this way.

await ElasticClient.IndexAsync<FirstChild>(child, m => m.Index(IndexName));

And Also, I found this question on SO for retrieving my entries from DB but it is outdated and the API is changed and no more accessible.

I want to know if it is a good approach to store sibling data in the same index how can I do this properly.

Answer 1

As of ES 6.0, it is not possible anymore to store multiple types inside the same index, i.e. the _type field you're referring to will always be either doc or _doc. In ES 8.0, the _type field will be removed altogether.

However, if it makes sense for your use case, you can still decide to store several types inside a single index using a custom type field that is present in your document.

You should strive to only store in the same index data that share the same (or very similar) mapping, which doesn't seem to be the case for Parent, FirstChild and SecondChild, but if you add a public string type property to your classes you can still do it.