Module collector

Expand description

§Collectors

Collectors define the information you want to extract from the documents matching the queries. In tantivy jargon, we call this information your search “fruit”.

Your fruit could for instance be :

At some point in your code, you will trigger the actual search operation by calling Searcher::search(). This call will look like this:

let fruit = searcher.search(&query, &collector)?;

Here the type of fruit is actually determined as an associated type of the collector (Collector::Fruit).

§Combining several collectors

A rich search experience often requires to run several collectors on your search query. For instance,

selecting the top-K products matching your query
counting the matching documents
computing several facets
computing statistics about the matching product prices

A simple and efficient way to do that is to pass your collectors as one tuple. The resulting Fruit will then be a typed tuple with each collector’s original fruits in their respective position.

use tantivy::collector::{Count, TopDocs};
let (doc_count, top_docs): (usize, Vec<(Score, DocAddress)>) =
searcher.search(&query, &(Count, TopDocs::with_limit(2)))?;

The Collector trait is implemented for up to 4 collectors. If you have more than 4 collectors, you can either group them into tuples of tuples (a,(b,(c,d))), or rely on MultiCollector.

§Combining several collectors dynamically

Combining collectors into a tuple is a zero-cost abstraction: everything happens as if you had manually implemented a single collector combining all of our features.

Unfortunately it requires you to know at compile time your collector types. If on the other hand, the collectors depend on some query parameter, you can rely on MultiCollector’s.

§Implementing your own collectors.

See the custom_collector example.

Structs§

BytesFilterCollector: A variant of the FilterCollector specialized for bytes fast fields, i.e.
ComparableDoc: Contains a feature (field, score, etc.) of a document along with the document address.
Count: CountCollector collector only counts how many documents match the query.
DocSetCollector: Collectors that returns the set of DocAddress that matches the query.
FacetCollector: Collector for faceting
FacetCounts: Intermediary result of the FacetCollector that stores the facet counts for all the segments.
FilterCollector: The FilterCollector filters docs using a fast field value and a predicate.
FruitHandle: FruitHandle stores reference to the corresponding collector inside MultiCollector
HistogramCollector: Histogram builds an histogram of the values of a fastfield for the collected DocSet.
MultiCollector: Multicollector makes it possible to collect on more than one collector. It should only be used for use cases where the Collector types is unknown at compile time.
MultiFruit: MultiFruit keeps Fruits from every nested Collector
TopDocs: The TopDocs collector keeps track of the top K documents sorted by their score.
TopNComputer: Fast TopN Computation

Traits§

Collector: Collectors are in charge of collecting and retaining relevant information from the document found and scored by the query.
CustomScorer: CustomScorer makes it possible to define any kind of score.
CustomSegmentScorer: A custom segment scorer makes it possible to define any kind of score for a given document belonging to a specific segment.
Fruit: Fruit is the type for the result of our collection. e.g. usize for the Count collector.
ScoreSegmentTweaker: A ScoreSegmentTweaker makes it possible to modify the default score for a given document belonging to a specific segment.
ScoreTweaker: ScoreTweaker makes it possible to tweak the score emitted by the scorer into another one.
SegmentCollector: The SegmentCollector is the trait in charge of defining the collect operation at the scale of the segment.