While the mapping and to_indexed_json methods are related, they serve two different purposes, in fact.
The purpose of the mapping method is to define mapping for the document properties within an index. You may want to define certain property as "not_analyzed", so it is not broken into tokens, or set a specific analyzer for the property, or (as you mention) indexing time boost factor. You may also define multifield property, custom formats for date types, etc.
This mapping is then used eg. when Tire automatically creates an index for your model.
The purpose of the to_indexed_json method is to define a JSON serialization for your documents/models.
The default to_indexed_json method does use your mapping definition, to use only properties defined in the mapping — on a basis that if you care enough to define the mapping, by default Tire indexes only properties with defined mapping.
Now, when you want a tight grip on how your model is in fact serialized into JSON for elasticsearch, you just define your own to_indexed_json methods (as the README instructs).
This custom MyModel#to_indexed_method usually does not care about mapping definition, and builds the JSON serialization from scratch (by leveraging ActiveRecord's to_json, using a JSON builder such as jbuilder, or just building a plain old Hash and calling Hash#to_json).
So, to answer the last part of your question, using both mapping and to_indexed_json will absolutely not create any conflicts, and is in fact required to use advanced features in elasticsearch.
To sum up:
- You use the
mapping method to define the mapping for your models for the search engine
- You use a custom
to_indexed_json method to define how the search engine sees your documents/models.
