Polishing.

Fix method order from earlier merges. Add missing Javadoc. Simplify tests. Update documentation.

See #3721
Original pull request: #3746.

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

@@ -155,6 +155,46 @@ public class ArithmeticOperators {
 			return usesFieldRef() ? Ceil.ceilValueOf(fieldReference) : Ceil.ceilValueOf(expression);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the mathematical derivative value.
+		 *
+		 * @return new instance of {@link Derivative}.
+		 * @since 3.3
+		 */
+		public Derivative derivative() {
+			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));
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the mathematical derivative value.
+		 *
+		 * @param unit The time unit ({@literal week, day, hour, minute, second, millisecond}) to apply can be
+		 *          {@literal null}.
+		 * @return new instance of {@link Derivative}.
+		 * @since 3.3
+		 */
+		public Derivative derivative(@Nullable String unit) {
+
+			Derivative derivative = usesFieldRef() ? Derivative.derivativeOf(fieldReference)
+					: Derivative.derivativeOf(expression);
+			return StringUtils.hasText(unit) ? derivative.unit(unit) : derivative;
+		}
+
 		/**
 		 * Creates new {@link AggregationExpression} that ivides the associated number by number referenced via
 		 * {@literal fieldReference}.
@@ -226,6 +266,21 @@ public class ArithmeticOperators {
 			return usesFieldRef() ? Integral.integralOf(fieldReference) : Integral.integralOf(expression);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the approximation for the mathematical integral 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 Integral integral(WindowUnit unit) {
+
+			Assert.notNull(unit, "Window unit must not be null");
+
+			return integral(unit.name().toLowerCase(Locale.ROOT));
+		}
+
 		/**
 		 * Creates new {@link AggregationExpression} that calculates the approximation for the mathematical integral value.
 		 *
@@ -234,6 +289,9 @@ public class ArithmeticOperators {
 		 * @since 3.3
 		 */
 		public Integral integral(String unit) {
+
+			Assert.hasText(unit, "Unit must not be empty!");
+
 			return integral().unit(unit);
 		}
 
@@ -618,46 +676,6 @@ public class ArithmeticOperators {
 			return round().place(place);
 		}
 
-		/**
-		 * Creates new {@link AggregationExpression} that calculates the mathematical derivative value.
-		 *
-		 * @return new instance of {@link Derivative}.
-		 * @since 3.3
-		 */
-		public Derivative derivative() {
-			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));
-		}
-
-		/**
-		 * Creates new {@link AggregationExpression} that calculates the mathematical derivative value.
-		 *
-		 * @param unit The time unit ({@literal week, day, hour, minute, second, millisecond}) to apply can be
-		 *          {@literal null}.
-		 * @return new instance of {@link Derivative}.
-		 * @since 3.3
-		 */
-		public Derivative derivative(@Nullable String unit) {
-
-			Derivative derivative = usesFieldRef() ? Derivative.derivativeOf(fieldReference)
-					: Derivative.derivativeOf(expression);
-			return StringUtils.hasText(unit) ? derivative.unit(unit) : derivative;
-		}
-
 		private boolean usesFieldRef() {
 			return fieldReference != null;
 		}
@@ -1792,16 +1810,36 @@ public class ArithmeticOperators {
 		}
 	}
 
+	/**
+	 * Value object to represent an {@link AggregationExpression expression} that calculates the average rate of change
+	 * within the specified window.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
 	public static class Derivative extends AbstractAggregationExpression {
 
 		private Derivative(Object value) {
 			super(value);
 		}
 
+		/**
+		 * Create a new instance of {@link Derivative} for the value stored at the given field holding a numeric value.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link Derivative}.
+		 */
 		public static Derivative derivativeOf(String fieldReference) {
 			return new Derivative(Collections.singletonMap("input", Fields.field(fieldReference)));
 		}
 
+		/**
+		 * Create a new instance of {@link Derivative} for the value provided by the given expression that resolves to a
+		 * numeric value.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link Derivative}.
+		 */
 		public static Derivative derivativeOf(AggregationExpression expression) {
 			return new Derivative(Collections.singletonMap("input", expression));
 		}

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

@@ -15,8 +15,8 @@
  */
 package org.springframework.data.mongodb.core.aggregation;
 
-import static org.assertj.core.api.Assertions.*;
 import static org.springframework.data.mongodb.core.aggregation.ArithmeticOperators.*;
+import static org.springframework.data.mongodb.test.util.Assertions.*;
 
 import java.util.Arrays;
 import java.util.Collections;
@@ -66,16 +66,19 @@ class ArithmeticOperatorsUnitTests {
 
 		assertThat(
 				valueOf("miles").derivative(SetWindowFieldsOperation.WindowUnits.HOUR).toDocument(Aggregation.DEFAULT_CONTEXT))
-				.isEqualTo(Document.parse("{ $derivative: { input: \"$miles\", unit: \"hour\" } }"));
+						.isEqualTo("{ $derivative: { input: \"$miles\", unit: \"hour\" } }");
 	}
 
 	@Test // GH-3721
 	void rendersIntegral() {
-		assertThat(valueOf("kilowatts").integral().toDocument(Aggregation.DEFAULT_CONTEXT)).isEqualTo(Document.parse("{ $integral : { input : \"$kilowatts\" } }"));
+		assertThat(valueOf("kilowatts").integral().toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo("{ $integral : { input : \"$kilowatts\" } }");
 	}
 
 	@Test // GH-3721
 	void rendersIntegralWithUnit() {
-		assertThat(valueOf("kilowatts").integral("hour").toDocument(Aggregation.DEFAULT_CONTEXT)).isEqualTo(Document.parse("{ $integral : { input : \"$kilowatts\", unit : \"hour\" } }"));
+		assertThat(valueOf("kilowatts").integral(SetWindowFieldsOperation.WindowUnits.HOUR)
+				.toDocument(Aggregation.DEFAULT_CONTEXT))
+						.isEqualTo("{ $integral : { input : \"$kilowatts\", unit : \"hour\" } }");
 	}
 }

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

@@ -23,8 +23,8 @@ import org.bson.Document;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
+
 import org.springframework.data.mongodb.core.Person;
-import org.springframework.lang.Nullable;
 
 /**
  * Unit tests for {@link SpelExpressionTransformer}.
@@ -152,8 +152,8 @@ public class SpelExpressionTransformerUnitTests {
 	@Test // DATAMONGO-774
 	void shouldRenderConsecutiveOperationsInComplexExpression() {
 
-		assertThat(transform("1 + 1 + (1 + 1 + 1) / q")).isEqualTo(
-				Document.parse("{ \"$add\" : [ 1 , 1 , { \"$divide\" : [ { \"$add\" : [ 1 , 1 , 1]} , \"$q\"]}]}"));
+		assertThat(transform("1 + 1 + (1 + 1 + 1) / q"))
+				.isEqualTo(Document.parse("{ \"$add\" : [ 1 , 1 , { \"$divide\" : [ { \"$add\" : [ 1 , 1 , 1]} , \"$q\"]}]}"));
 	}
 
 	@Test // DATAMONGO-774
@@ -189,8 +189,7 @@ public class SpelExpressionTransformerUnitTests {
 
 		Person person = new Person();
 		person.setAge(10);
-		assertThat(transform("[0].age + a.c", person))
-				.isEqualTo(Document.parse("{ \"$add\" : [ 10 , \"$a.c\"] }"));
+		assertThat(transform("[0].age + a.c", person)).isEqualTo(Document.parse("{ \"$add\" : [ 10 , \"$a.c\"] }"));
 	}
 
 	@Test // DATAMONGO-840
@@ -216,8 +215,7 @@ public class SpelExpressionTransformerUnitTests {
 
 	@Test // DATAMONGO-1530
 	void shouldRenderMethodReferenceNodeSetEquals() {
-		assertThat(transform("setEquals(a, b)"))
-				.isEqualTo(Document.parse("{ \"$setEquals\" : [ \"$a\" , \"$b\"]}"));
+		assertThat(transform("setEquals(a, b)")).isEqualTo(Document.parse("{ \"$setEquals\" : [ \"$a\" , \"$b\"]}"));
 	}
 
 	@Test // DATAMONGO-1530
@@ -379,8 +377,7 @@ public class SpelExpressionTransformerUnitTests {
 
 	@Test // DATAMONGO-1530
 	void shouldRenderMethodReferenceNodeConcat() {
-		assertThat(transform("concat(a, b, 'c')"))
-				.isEqualTo(Document.parse("{ \"$concat\" : [ \"$a\" , \"$b\" , \"c\"]}"));
+		assertThat(transform("concat(a, b, 'c')")).isEqualTo(Document.parse("{ \"$concat\" : [ \"$a\" , \"$b\" , \"c\"]}"));
 	}
 
 	@Test // DATAMONGO-1530
@@ -400,8 +397,7 @@ public class SpelExpressionTransformerUnitTests {
 
 	@Test // DATAMONGO-1530
 	void shouldRenderMethodReferenceNodeStrCaseCmp() {
-		assertThat(transform("strcasecmp(a, b)"))
-				.isEqualTo(Document.parse("{ \"$strcasecmp\" : [ \"$a\" , \"$b\"]}"));
+		assertThat(transform("strcasecmp(a, b)")).isEqualTo(Document.parse("{ \"$strcasecmp\" : [ \"$a\" , \"$b\"]}"));
 	}
 
 	@Test // DATAMONGO-1530
@@ -411,8 +407,7 @@ public class SpelExpressionTransformerUnitTests {
 
 	@Test // DATAMONGO-1530
 	void shouldRenderMethodReferenceNodeArrayElemAt() {
-		assertThat(transform("arrayElemAt(a, 10)"))
-				.isEqualTo(Document.parse("{ \"$arrayElemAt\" : [ \"$a\" , 10]}"));
+		assertThat(transform("arrayElemAt(a, 10)")).isEqualTo(Document.parse("{ \"$arrayElemAt\" : [ \"$a\" , 10]}"));
 	}
 
 	@Test // DATAMONGO-1530
@@ -511,15 +506,14 @@ public class SpelExpressionTransformerUnitTests {
 
 	@Test // DATAMONGO-1530
 	void shouldRenderMethodReferenceDateToString() {
-		assertThat(transform("dateToString('%Y-%m-%d', $date)")).isEqualTo(
-				Document.parse("{ \"$dateToString\" : { \"format\" : \"%Y-%m-%d\" , \"date\" : \"$date\"}}"));
+		assertThat(transform("dateToString('%Y-%m-%d', $date)"))
+				.isEqualTo(Document.parse("{ \"$dateToString\" : { \"format\" : \"%Y-%m-%d\" , \"date\" : \"$date\"}}"));
 	}
 
 	@Test // DATAMONGO-1530
 	void shouldRenderMethodReferenceCond() {
 		assertThat(transform("cond(qty > 250, 30, 20)")).isEqualTo(
-				Document
-				.parse("{ \"$cond\" : { \"if\" : { \"$gt\" : [ \"$qty\" , 250]} , \"then\" : 30 , \"else\" : 20}}"));
+				Document.parse("{ \"$cond\" : { \"if\" : { \"$gt\" : [ \"$qty\" , 250]} , \"then\" : 30 , \"else\" : 20}}"));
 	}
 
 	@Test // DATAMONGO-1530
@@ -633,8 +627,7 @@ public class SpelExpressionTransformerUnitTests {
 	@Test // DATAMONGO-1530
 	void shouldRenderComplexOperationNodeAnd() {
 		assertThat(transform("1+2 && concat(a, b) && true")).isEqualTo(
-				Document
-				.parse("{ \"$and\" : [ { \"$add\" : [ 1 , 2]} , { \"$concat\" : [ \"$a\" , \"$b\"]} , true]}"));
+				Document.parse("{ \"$and\" : [ { \"$add\" : [ 1 , 2]} , { \"$concat\" : [ \"$a\" , \"$b\"]} , true]}"));
 	}
 
 	@Test // DATAMONGO-1530
@@ -644,8 +637,7 @@ public class SpelExpressionTransformerUnitTests {
 
 	@Test // DATAMONGO-1530
 	void shouldRenderComplexNotCorrectly() {
-		assertThat(transform("!(foo > 10)"))
-				.isEqualTo(Document.parse("{ \"$not\" : [ { \"$gt\" : [ \"$foo\" , 10]}]}"));
+		assertThat(transform("!(foo > 10)")).isEqualTo(Document.parse("{ \"$not\" : [ { \"$gt\" : [ \"$foo\" , 10]}]}"));
 	}
 
 	@Test // DATAMONGO-1548
@@ -951,12 +943,14 @@ public class SpelExpressionTransformerUnitTests {
 
 	@Test // GH-3712
 	void shouldRenderCovariancePop() {
-		assertThat(transform("covariancePop(field1, field2)")).isEqualTo(Document.parse("{ \"$covariancePop\" : [\"$field1\", \"$field2\"]}"));
+		assertThat(transform("covariancePop(field1, field2)"))
+				.isEqualTo(Document.parse("{ \"$covariancePop\" : [\"$field1\", \"$field2\"]}"));
 	}
 
 	@Test // GH-3712
 	void shouldRenderCovarianceSamp() {
-		assertThat(transform("covarianceSamp(field1, field2)")).isEqualTo(Document.parse("{ \"$covarianceSamp\" : [\"$field1\", \"$field2\"]}"));
+		assertThat(transform("covarianceSamp(field1, field2)"))
+				.isEqualTo(Document.parse("{ \"$covarianceSamp\" : [\"$field1\", \"$field2\"]}"));
 	}
 
 	@Test // GH-3715
@@ -988,20 +982,21 @@ public class SpelExpressionTransformerUnitTests {
 				.isEqualTo(Document.parse("{ $shift: { output: \"$quantity\", by: 1, default: \"Not available\" } }"));
 	}
 
-	@Nullable
 	@Test // GH-3716
 	void shouldRenderDerivative() {
-		assertThat(transform("derivative(miles, 'hour')")).isEqualTo(Document.parse("{ \"$derivative\" : { input : '$miles', unit : 'hour'} }"));
+		assertThat(transform("derivative(miles, 'hour')"))
+				.isEqualTo(Document.parse("{ \"$derivative\" : { input : '$miles', unit : 'hour'} }"));
 	}
 
 	@Test // GH-3721
-	public void shouldRenderIntegral() {
+	void shouldRenderIntegral() {
 		assertThat(transform("integral(field)")).isEqualTo(Document.parse("{ \"$integral\" : { \"input\" : \"$field\" }}"));
 	}
 
 	@Test // GH-3721
-	public void shouldIntegralWithUnit() {
-		assertThat(transform("integral(field, 'hour')")).isEqualTo(Document.parse("{ \"$integral\" : { \"input\" : \"$field\", \"unit\" : \"hour\" }}"));
+	void shouldRenderIntegralWithUnit() {
+		assertThat(transform("integral(field, 'hour')"))
+				.isEqualTo(Document.parse("{ \"$integral\" : { \"input\" : \"$field\", \"unit\" : \"hour\" }}"));
 	}
 
 	private Object transform(String expression, Object... params) {

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`, `derivative`, `divide`, `exp`, `floor`, `ln`, `log`, `log10`, `mod`, `multiply`, `pow`, `round`, `sqrt`, `subtract` (+++*+++ via `minus`), `trunc`
+| `abs`, `add` (+++*+++ via `plus`), `ceil`, `derivative`, `divide`, `exp`, `floor`, `integral`, `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`