> ## Documentation Index
> Fetch the complete documentation index at: https://nikita-shkoda.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# Model configuration
> Define collections, fields, identity, and defaults.
Related: Models, Schema, Configuration
Use this page when you are defining a new SearchEngine model or expanding an existing one.
## Define the collection and fields
```ruby app/search_engine/book.rb theme={null}
class SearchEngine::Book < SearchEngine::Base
collection :books
attribute :sku, :string
attribute :name, :string, sort: true
attribute :description, :string
attribute :publisher_id, :string
attribute :price, :float
attribute :tags, [:string], empty_filtering: true
attribute :store, :object, nested: { name: :string, city: :string }
end
```
Do not declare attribute :id. Use identify\_by to control the Typesense document id.
## Set identity and defaults
```ruby app/search_engine/book.rb theme={null}
class SearchEngine::Book < SearchEngine::Base
# ... attributes ...
identify_by :sku
query_by :name, :description
schema_retention keep_last: 2
end
```
* identify\_by controls the Typesense document id.
* query\_by sets a per-model default for searches.
* schema\_retention keeps old physical collections after swaps.
## Nested fields
Use :object or \[:object] with nested: to define subfields.
```ruby app/search_engine/book.rb theme={null}
class SearchEngine::Book < SearchEngine::Base
attribute :retail_prices, [:object], nested: {
current_price: :float,
price_type: :string
}
end
```
## Next steps
* Validate field types and options in Schema.
* Use Indexer to map and import data.