Add a basic faceted search example (#383)

* Add a basic faceted search example

* quieting the compiler

examples/faceted_search.rs

@@ -0,0 +1,81 @@
+// # Basic Example
+//
+// This example covers the basic functionalities of
+// tantivy.
+//
+// We will :
+// - define our schema
+// = create an index in a directory
+// - index few documents in our index
+// - search for the best document matchings "sea whale"
+// - retrieve the best document original content.
+
+extern crate tempdir;
+
+// ---
+// Importing tantivy...
+#[macro_use]
+extern crate tantivy;
+use tantivy::collector::FacetCollector;
+use tantivy::query::AllQuery;
+use tantivy::schema::*;
+use tantivy::Index;
+
+fn main() -> tantivy::Result<()> {
+  // Let's create a temporary directory for the
+  // sake of this example
+  let index_path = TempDir::new("tantivy_facet_example_dir")?;
+  let mut schema_builder = SchemaBuilder::default();
+
+  schema_builder.add_text_field("name", TEXT | STORED);
+
+  // this is our faceted field
+  schema_builder.add_facet_field("tags");
+
+  let schema = schema_builder.build();
+
+  let index = Index::create_in_dir(&index_path, schema.clone())?;
+
+  let mut index_writer = index.writer(50_000_000)?;
+
+  let name = schema.get_field("name").unwrap();
+  let tags = schema.get_field("tags").unwrap();
+
+  // For convenience, tantivy also comes with a macro to
+  // reduce the boilerplate above.
+  index_writer.add_document(doc!(
+        name => "the ditch",
+        tags => Facet::from("/pools/north")
+    ));
+
+  index_writer.add_document(doc!(
+        name => "little stacey",
+        tags => Facet::from("/pools/south")
+    ));
+
+  index_writer.commit()?;
+
+  index.load_searchers()?;
+
+  let searcher = index.searcher();
+
+  let mut facet_collector = FacetCollector::for_field(tags);
+  facet_collector.add_facet("/pools");
+
+  searcher.search(&AllQuery, &mut facet_collector).unwrap();
+
+  let counts = facet_collector.harvest();
+  // This lists all of the facet counts
+  let facets: Vec<(&Facet, u64)> = counts.get("/pools").collect();
+  assert_eq!(
+    facets,
+    vec![
+      (&Facet::from("/pools/north"), 1),
+      (&Facet::from("/pools/south"), 1)
+    ]
+  );
+
+  Ok(())
+}
+
+use tempdir::TempDir;

examples/working_with_json.rs

@@ -1,7 +1,6 @@
 extern crate tantivy;
 use tantivy::schema::*;
 
-
 // # Document from json
 //
 // For convenience, `Document` can be parsed directly from json.
@@ -23,8 +22,8 @@ fn main() -> tantivy::Result<()> {
     }"#;
 
     // We can parse our document
-    let mice_and_men_doc = schema.parse_document(&mice_and_men_doc_json)?;
-        
+    let _mice_and_men_doc = schema.parse_document(&mice_and_men_doc_json)?;
+
     // Multi-valued field are allowed, they are
     // expressed in JSON by an array.
     // The following document has two titles.
@@ -32,8 +31,7 @@ fn main() -> tantivy::Result<()> {
        "title": ["Frankenstein", "The Modern Prometheus"],
        "year": 1818
     }"#;
-    let frankenstein_doc = schema.parse_document(&frankenstein_json)?;
-
+    let _frankenstein_doc = schema.parse_document(&frankenstein_json)?;
 
     // Note that the schema is saved in your index directory.
     //