Add support for $dateTrunc aggregation operator.

See #4139
Original pull request: #4182.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/DateOperators.java

@@ -538,6 +538,32 @@ public class DateOperators {
 					DateSubtract.subtractValue(value, unit.name().toLowerCase(Locale.ROOT)).fromDate(dateReference()), timezone);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that truncates a date to the given {@literal unit}.
+		 *
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 * @since 4.0
+		 */
+		public DateTrunc truncate(String unit) {
+
+			Assert.notNull(unit, "TemporalUnit must not be null");
+			return applyTimezone(DateTrunc.truncateValue(dateReference()).to(unit), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that truncates a date to the given {@literal unit}.
+		 *
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 * @since 4.0
+		 */
+		public DateTrunc truncate(TemporalUnit unit) {
+
+			Assert.notNull(unit, "TemporalUnit must not be null");
+			return truncate(unit.name().toLowerCase(Locale.ROOT));
+		}
+
 		/**
 		 * Creates new {@link AggregationExpression} that returns the day of the year for a date as a number between 1 and
 		 * 366.
@@ -3027,6 +3053,135 @@ public class DateOperators {
 		}
 	}
 
+	/**
+	 * {@link AggregationExpression} for {@code $dateTrunc}.<br />
+	 * <strong>NOTE:</strong> Requires MongoDB 5.0 or later.
+	 *
+	 * @author Christoph Strobl
+	 * @since 4.0
+	 */
+	public static class DateTrunc extends TimezonedDateAggregationExpression {
+
+		private DateTrunc(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Truncates the date value of computed by the given {@link AggregationExpression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public static DateTrunc truncateValueOf(AggregationExpression expression) {
+			return truncateValue(expression);
+		}
+
+		/**
+		 * Truncates the date value of the referenced {@literal field}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public static DateTrunc truncateValueOf(String fieldReference) {
+			return truncateValue(Fields.field(fieldReference));
+		}
+
+		/**
+		 * Truncates the date value.
+		 *
+		 * @param value must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public static DateTrunc truncateValue(Object value) {
+			return new DateTrunc(Collections.singletonMap("date", value));
+		}
+
+		/**
+		 * Define the unit of time.
+		 *
+		 * @param unit must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public DateTrunc to(String unit) {
+			return new DateTrunc(append("unit", unit));
+		}
+
+		/**
+		 * Define the unit of time via an {@link AggregationExpression}.
+		 *
+		 * @param unit must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public DateTrunc to(AggregationExpression unit) {
+			return new DateTrunc(append("unit", unit));
+		}
+
+		/**
+		 * Define the weeks starting day if {@link #to(String)} resolves to {@literal week}.
+		 *
+		 * @param day must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public DateTrunc startOfWeek(java.time.DayOfWeek day) {
+			return startOfWeek(day.name().toLowerCase(Locale.US));
+		}
+
+		/**
+		 * Define the weeks starting day if {@link #to(String)} resolves to {@literal week}.
+		 *
+		 * @param day must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public DateTrunc startOfWeek(String day) {
+			return new DateTrunc(append("startOfWeek", day));
+		}
+
+		/**
+		 * Define the numeric time value.
+		 *
+		 * @param binSize must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public DateTrunc binSize(int binSize) {
+			return binSize((Object) binSize);
+		}
+
+		/**
+		 * Define the numeric time value via an {@link AggregationExpression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public DateTrunc binSize(AggregationExpression expression) {
+			return binSize((Object) expression);
+		}
+
+		/**
+		 * Define the numeric time value.
+		 *
+		 * @param binSize must not be {@literal null}.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public DateTrunc binSize(Object binSize) {
+			return new DateTrunc(append("binSize", binSize));
+		}
+
+		/**
+		 * Optionally set the {@link Timezone} to use. If not specified {@literal UTC} is used.
+		 *
+		 * @param timezone must not be {@literal null}. Consider {@link Timezone#none()} instead.
+		 * @return new instance of {@link DateTrunc}.
+		 */
+		public DateTrunc withTimezone(Timezone timezone) {
+			return new DateTrunc(appendTimezone(argumentMap(), timezone));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$dateTrunc";
+		}
+	}
+
 	/**
 	 * Interface defining a temporal unit for date operators.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/spel/MethodReferenceNode.java

@@ -165,6 +165,8 @@ public class MethodReferenceNode extends ExpressionNode {
 				mapArgRef().forOperator("$dateSubtract").mappingParametersTo("startDate", "unit", "amount", "timezone"));
 		map.put("dateDiff", mapArgRef().forOperator("$dateDiff").mappingParametersTo("startDate", "endDate", "unit",
 				"timezone", "startOfWeek"));
+		map.put("dateTrunc",
+				mapArgRef().forOperator("$dateTrunc").mappingParametersTo("date", "unit", "binSize", "startOfWeek", "timezone"));
 		map.put("dayOfYear", singleArgRef().forOperator("$dayOfYear"));
 		map.put("dayOfMonth", singleArgRef().forOperator("$dayOfMonth"));
 		map.put("dayOfWeek", singleArgRef().forOperator("$dayOfWeek"));

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/DateOperatorsUnitTests.java

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.core.aggregation;
 
 import static org.springframework.data.mongodb.test.util.Assertions.*;
 
+import java.time.DayOfWeek;
 import java.time.ZoneId;
 import java.time.ZoneOffset;
 import java.time.temporal.ChronoUnit;
@@ -24,6 +25,7 @@ import java.util.TimeZone;
 
 import org.junit.jupiter.api.Test;
 
+import org.springframework.data.mongodb.core.aggregation.DateOperators.TemporalUnit;
 import org.springframework.data.mongodb.core.aggregation.DateOperators.Timezone;
 
 /**
@@ -102,4 +104,18 @@ class DateOperatorsUnitTests {
 	void rendersTimezoneFromZoneId() {
 		assertThat(DateOperators.Timezone.fromZone(ZoneId.of("America/Chicago")).getValue()).isEqualTo("America/Chicago");
 	}
+
+	@Test // GH-4139
+	void rendersDateTrunc() {
+
+		assertThat(DateOperators.dateOf("purchaseDate").truncate("week").binSize(2).startOfWeek(DayOfWeek.MONDAY).toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo("{ $dateTrunc: { date: \"$purchaseDate\", unit: \"week\", binSize: 2, startOfWeek : \"monday\" } }");
+	}
+
+	@Test // GH-4139
+	void rendersDateTruncWithTimezone() {
+
+		assertThat(DateOperators.zonedDateOf("purchaseDate", Timezone.valueOf("America/Chicago")).truncate("week").binSize(2).startOfWeek(DayOfWeek.MONDAY).toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo("{ $dateTrunc: { date: \"$purchaseDate\", unit: \"week\", binSize: 2, startOfWeek : \"monday\", timezone : \"America/Chicago\" } }");
+	}
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/SpelExpressionTransformerUnitTests.java

@@ -1220,6 +1220,11 @@ public class SpelExpressionTransformerUnitTests {
 		assertThat(transform("minN(3, \"$score\")")).isEqualTo("{ $minN : { n : 3, input : \"$score\" }}");
 	}
 
+	@Test // GH-4139
+	void shouldRenderDateTrunc() {
+		assertThat(transform("dateTrunc(purchaseDate, \"week\", 2, \"monday\")")).isEqualTo("{ $dateTrunc : { date : \"$purchaseDate\", unit : \"week\", binSize : 2, startOfWeek : \"monday\" }}");
+	}
+
 	private Document transform(String expression, Object... params) {
 		return (Document) transformer.transform(expression, Aggregation.DEFAULT_CONTEXT, params);
 	}