add aggregation support for date type

examples/aggregation.rs

@@ -118,7 +118,7 @@ fn main() -> tantivy::Result<()> {
     .into_iter()
     .collect();
 
-    let collector = AggregationCollector::from_aggs(agg_req_1, None);
+    let collector = AggregationCollector::from_aggs(agg_req_1, None, index.schema());
 
     let searcher = reader.searcher();
     let agg_res: AggregationResults = searcher.search(&term_query, &collector).unwrap();

src/aggregation/agg_req_with_accessor.rs

@@ -11,7 +11,7 @@ use super::bucket::{HistogramAggregation, RangeAggregation, TermsAggregation};
 use super::metric::{AverageAggregation, StatsAggregation};
 use super::segment_agg_result::BucketCount;
 use super::VecWithNames;
-use crate::fastfield::{type_and_cardinality, FastType, MultiValuedFastFieldReader};
+use crate::fastfield::{type_and_cardinality, MultiValuedFastFieldReader};
 use crate::schema::{Cardinality, Type};
 use crate::{InvertedIndexReader, SegmentReader, TantivyError};
 
@@ -194,13 +194,7 @@ fn get_ff_reader_and_validate(
         .ok_or_else(|| TantivyError::FieldNotFound(field_name.to_string()))?;
     let field_type = reader.schema().get_field_entry(field).field_type();
 
-    if let Some((ff_type, field_cardinality)) = type_and_cardinality(field_type) {
-        if ff_type == FastType::Date {
-            return Err(TantivyError::InvalidArgument(
-                "Unsupported field type date in aggregation".to_string(),
-            ));
-        }
-
+    if let Some((_ff_type, field_cardinality)) = type_and_cardinality(field_type) {
         if cardinality != field_cardinality {
             return Err(TantivyError::InvalidArgument(format!(
                 "Invalid field cardinality on field {} expected {:?}, but got {:?}",

src/aggregation/agg_result.rs

@@ -12,6 +12,7 @@ use super::bucket::GetDocCount;
 use super::intermediate_agg_result::{IntermediateBucketResult, IntermediateMetricResult};
 use super::metric::{SingleMetricResult, Stats};
 use super::Key;
+use crate::schema::Schema;
 use crate::TantivyError;
 
 #[derive(Clone, Default, Debug, PartialEq, Serialize, Deserialize)]
@@ -129,9 +130,12 @@ pub enum BucketResult {
 }
 
 impl BucketResult {
-    pub(crate) fn empty_from_req(req: &BucketAggregationInternal) -> crate::Result<Self> {
+    pub(crate) fn empty_from_req(
+        req: &BucketAggregationInternal,
+        schema: &Schema,
+    ) -> crate::Result<Self> {
         let empty_bucket = IntermediateBucketResult::empty_from_req(&req.bucket_agg);
-        empty_bucket.into_final_bucket_result(req)
+        empty_bucket.into_final_bucket_result(req, schema)
     }
 }
 
@@ -174,6 +178,9 @@ pub enum BucketEntries<T> {
 /// ```
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 pub struct BucketEntry {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    /// The string representation of the bucket.
+    pub key_as_string: Option<String>,
     /// The identifier of the bucket.
     pub key: Key,
     /// Number of documents in the bucket.
@@ -238,4 +245,10 @@ pub struct RangeBucketEntry {
     /// The to range of the bucket. Equals `f64::MAX` when `None`.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub to: Option<f64>,
+    /// The optional string representation for the `from` range.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub from_as_string: Option<String>,
+    /// The optional string representation for the `to` range.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub to_as_string: Option<String>,
 }

src/aggregation/bucket/histogram/histogram.rs

@@ -10,12 +10,12 @@ use crate::aggregation::agg_req_with_accessor::{
     AggregationsWithAccessor, BucketAggregationWithAccessor,
 };
 use crate::aggregation::agg_result::BucketEntry;
-use crate::aggregation::f64_from_fastfield_u64;
 use crate::aggregation::intermediate_agg_result::{
     IntermediateAggregationResults, IntermediateBucketResult, IntermediateHistogramBucketEntry,
 };
 use crate::aggregation::segment_agg_result::SegmentAggregationResultsCollector;
-use crate::schema::Type;
+use crate::aggregation::{f64_from_fastfield_u64, format_date};
+use crate::schema::{Schema, Type};
 use crate::{DocId, TantivyError};
 
 /// Histogram is a bucket aggregation, where buckets are created dynamically for given `interval`.
@@ -451,6 +451,7 @@ fn intermediate_buckets_to_final_buckets_fill_gaps(
     buckets: Vec<IntermediateHistogramBucketEntry>,
     histogram_req: &HistogramAggregation,
     sub_aggregation: &AggregationsInternal,
+    schema: &Schema,
 ) -> crate::Result<Vec<BucketEntry>> {
     // Generate the full list of buckets without gaps.
     //
@@ -491,7 +492,9 @@ fn intermediate_buckets_to_final_buckets_fill_gaps(
                 sub_aggregation: empty_sub_aggregation.clone(),
             },
         })
-        .map(|intermediate_bucket| intermediate_bucket.into_final_bucket_entry(sub_aggregation))
+        .map(|intermediate_bucket| {
+            intermediate_bucket.into_final_bucket_entry(sub_aggregation, schema)
+        })
         .collect::<crate::Result<Vec<_>>>()
 }
 
@@ -500,20 +503,43 @@ pub(crate) fn intermediate_histogram_buckets_to_final_buckets(
     buckets: Vec<IntermediateHistogramBucketEntry>,
     histogram_req: &HistogramAggregation,
     sub_aggregation: &AggregationsInternal,
+    schema: &Schema,
 ) -> crate::Result<Vec<BucketEntry>> {
-    if histogram_req.min_doc_count() == 0 {
+    let mut buckets = if histogram_req.min_doc_count() == 0 {
         // With min_doc_count != 0, we may need to add buckets, so that there are no
         // gaps, since intermediate result does not contain empty buckets (filtered to
         // reduce serialization size).
 
-        intermediate_buckets_to_final_buckets_fill_gaps(buckets, histogram_req, sub_aggregation)
+        intermediate_buckets_to_final_buckets_fill_gaps(
+            buckets,
+            histogram_req,
+            sub_aggregation,
+            schema,
+        )?
     } else {
         buckets
             .into_iter()
             .filter(|histogram_bucket| histogram_bucket.doc_count >= histogram_req.min_doc_count())
-            .map(|histogram_bucket| histogram_bucket.into_final_bucket_entry(sub_aggregation))
-            .collect::<crate::Result<Vec<_>>>()
+            .map(|histogram_bucket| {
+                histogram_bucket.into_final_bucket_entry(sub_aggregation, schema)
+            })
+            .collect::<crate::Result<Vec<_>>>()?
+    };
+
+    // If we have a date type on the histogram buckets, we add the `key_as_string` field as rfc339
+    let field = schema
+        .get_field(&histogram_req.field)
+        .ok_or_else(|| TantivyError::FieldNotFound(histogram_req.field.to_string()))?;
+    if schema.get_field_entry(field).field_type().is_date() {
+        for bucket in buckets.iter_mut() {
+            if let crate::aggregation::Key::F64(val) = bucket.key {
+                let key_as_string = format_date(val as i64)?;
+                bucket.key_as_string = Some(key_as_string);
+            }
+        }
     }
+
+    Ok(buckets)
 }
 
 /// Applies req extended_bounds/hard_bounds on the min_max value
@@ -1372,6 +1398,63 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn histogram_date_test_single_segment() -> crate::Result<()> {
+        histogram_date_test_with_opt(true)
+    }
+
+    #[test]
+    fn histogram_date_test_multi_segment() -> crate::Result<()> {
+        histogram_date_test_with_opt(false)
+    }
+
+    fn histogram_date_test_with_opt(merge_segments: bool) -> crate::Result<()> {
+        let index = get_test_index_2_segments(merge_segments)?;
+
+        let agg_req: Aggregations = vec![(
+            "histogram".to_string(),
+            Aggregation::Bucket(BucketAggregation {
+                bucket_agg: BucketAggregationType::Histogram(HistogramAggregation {
+                    field: "date".to_string(),
+                    interval: 86400000000.0, // one day in microseconds
+                    ..Default::default()
+                }),
+                sub_aggregation: Default::default(),
+            }),
+        )]
+        .into_iter()
+        .collect();
+
+        let agg_res = exec_request(agg_req, &index)?;
+
+        let res: Value = serde_json::from_str(&serde_json::to_string(&agg_res)?)?;
+
+        assert_eq!(res["histogram"]["buckets"][0]["key"], 1546300800000000.0);
+        assert_eq!(
+            res["histogram"]["buckets"][0]["key_as_string"],
+            "2019-01-01T00:00:00Z"
+        );
+        assert_eq!(res["histogram"]["buckets"][0]["doc_count"], 1);
+
+        assert_eq!(res["histogram"]["buckets"][1]["key"], 1546387200000000.0);
+        assert_eq!(
+            res["histogram"]["buckets"][1]["key_as_string"],
+            "2019-01-02T00:00:00Z"
+        );
+
+        assert_eq!(res["histogram"]["buckets"][1]["doc_count"], 5);
+
+        assert_eq!(res["histogram"]["buckets"][2]["key"], 1546473600000000.0);
+        assert_eq!(
+            res["histogram"]["buckets"][2]["key_as_string"],
+            "2019-01-03T00:00:00Z"
+        );
+
+        assert_eq!(res["histogram"]["buckets"][3], Value::Null);
+
+        Ok(())
+    }
+
     #[test]
     fn histogram_invalid_request() -> crate::Result<()> {
         let index = get_test_index_2_segments(true)?;