Phrase search

phrase_search(field, phrase, k) matches documents whose field contains the phrase’s tokens consecutively and in order — a positional check, not a bag-of-words AND:

# use corvid::{Db, Value};
# let db = Db::open_in_memory()?; let c = db.collection("docs");
# let mut m = std::collections::BTreeMap::new();
# m.insert("body".into(), Value::Text("an embedded database for rust".into()));
# c.insert(b"d1", &Value::Map(m))?;
c.phrase_search("body", "embedded database", 10)?;   // matches d1
c.phrase_search("body", "database embedded", 10)?;   // order matters — no match
c.phrase_search("body", "embedded", 10)?;            // single term == term search
# Ok::<(), corvid::Error>(())

Semantics

• Single-term phrases equal term search.
• Repeated terms must actually repeat: "rust rust" does not match a single rust.
• Non-adjacent tokens do not match: "database for" does not match database for rust? It does — for may be a stop word (below). But "database rust" (skipping a kept word) does not.
• k bounds: k = 0 yields nothing; beyond the corpus yields everything that matches. An empty phrase yields nothing.
• Both index arms (in-RAM and on-disk postings carry positions) and the no-index fallback behave identically; the fallback scores hits with BM25 on the same scale as the indexed paths, so scores are comparable and creating or dropping an index does not reorder the same phrase query.

The stop-word collapse caveat

Token positions are assigned after stop-word removal, and there is no position gap for a removed stop word. Therefore phrases match across removed stop words:

"quick the brown" matches text containing "quick brown".

the never got a position, so quick and brown are adjacent in the positional stream. This is documented, pinned behavior — design phrase queries accordingly (avoid stop words inside phrases when adjacency matters against the raw text).

Sentence boundaries

Phrase matching does not respect sentence boundaries — positions continue across sentence-internal punctuation in the same field, so a phrase can match across a period if the tokens are adjacent in the stream. Pin your expectations with tests if you rely on boundary behavior.

CJK phrases

Over CJK bigrams, phrase order is order-correct: 東京タワー matches, タワー東京 does not (see tokenization).

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