Polishing.

Accept window units in addition to plain strings. Document operator.

See: #3716
Original pull request: #3742.

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

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.core.aggregation;
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 
 import org.springframework.data.mongodb.core.aggregation.AccumulatorOperators.Avg;
 import org.springframework.data.mongodb.core.aggregation.AccumulatorOperators.CovariancePop;
@@ -26,6 +27,8 @@ import org.springframework.data.mongodb.core.aggregation.AccumulatorOperators.Mi
 import org.springframework.data.mongodb.core.aggregation.AccumulatorOperators.StdDevPop;
 import org.springframework.data.mongodb.core.aggregation.AccumulatorOperators.StdDevSamp;
 import org.springframework.data.mongodb.core.aggregation.AccumulatorOperators.Sum;
+import org.springframework.data.mongodb.core.aggregation.SetWindowFieldsOperation.WindowUnit;
+import org.springframework.data.mongodb.core.aggregation.SetWindowFieldsOperation.WindowUnits;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
@@ -34,6 +37,7 @@ import org.springframework.util.StringUtils;
  * Gateway to {@literal Arithmetic} aggregation operations that perform math operations on numbers.
  *
  * @author Christoph Strobl
+ * @author Mark Paluch
  * @since 1.10
  */
 public class ArithmeticOperators {
@@ -600,7 +604,22 @@ public class ArithmeticOperators {
 		 * @since 3.3
 		 */
 		public Derivative derivative() {
-			return derivative(null);
+			return derivative((String) null);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the mathematical derivative value.
+		 *
+		 * @param unit The time unit ({@link WindowUnits#WEEK}, {@link WindowUnits#DAY}, {@link WindowUnits#HOUR},
+		 *          {@link WindowUnits#MINUTE}, {@link WindowUnits#SECOND}, {@link WindowUnits#MILLISECOND}) to apply.
+		 * @return new instance of {@link Derivative}.
+		 * @since 3.3
+		 */
+		public Derivative derivative(WindowUnit unit) {
+
+			Assert.notNull(unit, "Window unit must not be null");
+
+			return derivative(unit.name().toLowerCase(Locale.ROOT));
 		}
 
 		/**

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

@@ -28,8 +28,9 @@ import org.junit.jupiter.api.Test;
  * Unit tests for {@link Round}.
  *
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
-public class ArithmeticOperatorsUnitTests {
+class ArithmeticOperatorsUnitTests {
 
 	@Test // DATAMONGO-2370
 	void roundShouldWithoutPlace() {
@@ -63,7 +64,8 @@ public class ArithmeticOperatorsUnitTests {
 	@Test // GH-3716
 	void rendersDerivativeCorrectly() {
 
-		assertThat(valueOf("miles").derivative("hour").toDocument(Aggregation.DEFAULT_CONTEXT))
+		assertThat(
+				valueOf("miles").derivative(SetWindowFieldsOperation.WindowUnits.HOUR).toDocument(Aggregation.DEFAULT_CONTEXT))
 				.isEqualTo(Document.parse("{ $derivative: { input: \"$miles\", unit: \"hour\" } }"));
 	}
 }

src/main/asciidoc/reference/aggregation-framework.adoc

@@ -85,7 +85,7 @@ At the time of this writing, we provide support for the following Aggregation Op
 | `addToSet`, `covariancePop`, `covarianceSamp`, `expMovingAvg`, `first`, `last`, `max`, `min`, `avg`, `push`, `sum`, `count` (+++*+++), `stdDevPop`, `stdDevSamp`
 
 | Arithmetic Aggregation Operators
-| `abs`, `add` (+++*+++ via `plus`), `ceil`, `divide`, `exp`, `floor`, `ln`, `log`, `log10`, `mod`, `multiply`, `pow`, `round`, `sqrt`, `subtract` (+++*+++ via `minus`), `trunc`
+| `abs`, `add` (+++*+++ via `plus`), `ceil`, `derivative`, `divide`, `exp`, `floor`, `ln`, `log`, `log10`, `mod`, `multiply`, `pow`, `round`, `sqrt`, `subtract` (+++*+++ via `minus`), `trunc`
 
 | String Aggregation Operators
 | `concat`, `substr`, `toLower`, `toUpper`, `stcasecmp`, `indexOfBytes`, `indexOfCP`, `split`, `strLenBytes`, `strLenCP`, `substrCP`, `trim`, `ltrim`, `rtim`
@@ -119,6 +119,7 @@ At the time of this writing, we provide support for the following Aggregation Op
 
 | Script Aggregation Operators
 | `function`, `accumulator`
+
 |===
 
 +++*+++ The operation is mapped or added by Spring Data MongoDB.