How to store data in elasticsearch _source but not index it?

Question

I am searching only by couple of fields but I want to be able to store the whole document in ES in order not to additional DB (MySQL) queries.

I tried adding index: no, store: no to whole objects/properties in the mapping but I'm still not sure if the fields are being indexed and add unnecessary overhead.

Let's say I've got books and each has an author. I want to search only by book title, but I want to be able to retrieve the whole document.

Is this okay:

mappings:
properties:
    title:
        type: string
        index: analyzed
    author:
        type: object
        index: no
        store: no
        properties:
            first_name:
                type: string
            last_name:
                type: string

Or should I rather do:

mappings:
properties:
    title:
        type: string
        index: analyzed
    author:
        type: object
        properties:
            first_name:
                index: no
                store: no
                type: string
            last_name:
                index: no
                store: no
                type: string

Or maybe I am doing it completely wrong? And what about nested properties that should not be indexed?

Answer 1

By default the _source of the document is stored regardless of the fields that you choose to index. The _source is used to return the document in the search results, whereas the fields that are indexed are used for searching.

You can't set index: no on an object to prevent all fields in an object being indexed, but you can do what you want with Dynamic Templates using path_match property to apply the index: no setting to every field within an object. Here is a simple example.

Create an index with your mapping that includes the dynamic templates for the author object and the nested categories object:

POST /shop
{
    "mappings": {
        "book": {
            "dynamic_templates": [
                {
                    "author_object_template": {
                        "path_match": "author.*",
                        "mapping": {
                            "index": "no"
                        }
                    }
                },
                {
                    "categories_object_template": {
                        "path_match": "categories.*",
                        "mapping": {
                            "index": "no"
                        }
                    }
                }
            ],
            "properties": {
                "categories": {
                    "type": "nested"
                }
            }
        }
    }
}

Index a document:

POST /shop/book/1
{
    "title": "book one",
    "author": {
        "first_name": "jon",
        "last_name": "doe"
    },
    "categories": [
        {
            "cat_id": 1,
            "cat_name": "category one"
        },
        {
            "cat_id": 2,
            "cat_name": "category two"
        }
    ]
}

If you searched on the title field with the search term book the document would be returned. If you search on the author.first_name or author.last_name, there won't be a match because this fields were not indexed:

POST /shop/book/_search
{
    "query": {
        "match": {
            "author.first_name": "jon"
        }
    }
}

The same would be the case for a nested query on the category fields:

POST /shop/book/_search
{
    "query": {
        "nested": {
            "path": "categories",
            "query": {
                "match": {
                    "categories.cat_name": "category"
                }
            }
        }
    }
}

Also you can use the Luke tool to expect the Lucene index and see what fields have been indexed.