Add support for $sortArray aggregation operator.

See #4139
Original pull request: #4182.

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

@@ -23,6 +23,7 @@
 
 import org.bson.Document;
 import org.springframework.data.domain.Range;
+import org.springframework.data.domain.Sort;
 import org.springframework.data.mongodb.core.aggregation.ArrayOperators.Filter.AsBuilder;
 import org.springframework.data.mongodb.core.aggregation.ArrayOperators.Reduce.PropertyExpression;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.ExposedField;
@@ -315,6 +316,21 @@ public ArrayOperatorFactory.ReduceInitialValueBuilder reduce(PropertyExpression.
 					.withInitialValue(initialValue).reduce(expressions);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated array and sorts it by the given {@link Sort order}.
+		 *
+		 * @return new instance of {@link SortArray}.
+		 * @since 4.0
+		 */
+		public SortArray sort(Sort sort) {
+
+			if (usesFieldRef()) {
+				return SortArray.sortArrayOf(fieldReference).by(sort);
+			}
+
+			return (usesExpression() ? SortArray.sortArrayOf(expression) : SortArray.sortArray(values)).by(sort);
+		}
+
 		/**
 		 * Creates new {@link AggregationExpression} that transposes an array of input arrays so that the first element of
 		 * the output array would be an array containing, the first element of the first input array, the first element of
@@ -1915,4 +1931,66 @@ protected String getMongoMethod() {
 			return "$last";
 		}
 	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $sortArray} that sorts elements in an array. <br />
+	 *
+	 * @author Christoph Strobl
+	 * @since 4.0
+	 */
+	public static class SortArray extends AbstractAggregationExpression {
+
+		private SortArray(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Returns the given array.
+		 *
+		 * @param array must not be {@literal null}.
+		 * @return new instance of {@link SortArray}.
+		 */
+		public static SortArray sortArray(Object array) {
+			return new SortArray(Collections.singletonMap("input", array));
+		}
+
+		/**
+		 * Sorts the elements in the array pointed to by the given {@link Field field reference}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link SortArray}.
+		 */
+		public static SortArray sortArrayOf(String fieldReference) {
+			return sortArray(Fields.field(fieldReference));
+		}
+
+		/**
+		 * Sorts the elements of the array computed buy the given {@link AggregationExpression expression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link SortArray}.
+		 */
+		public static SortArray sortArrayOf(AggregationExpression expression) {
+			return sortArray(expression);
+		}
+
+		/**
+		 * Set the order to put elements in.
+		 * 
+		 * @param sort must not be {@literal null}.
+		 * @return new instance of {@link SortArray}.
+		 */
+		public SortArray by(Sort sort) {
+			return new SortArray(append("sortBy", sort));
+		}
+
+		/*
+		 * (non-Javadoc)
+		 * @see org.springframework.data.mongodb.core.aggregation.AbstractAggregationExpression#getMongoMethod()
+		 */
+		@Override
+		protected String getMongoMethod() {
+			return "$sortArray";
+		}
+	}
 }

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

@@ -142,6 +142,7 @@ public class MethodReferenceNode extends ExpressionNode {
 		map.put("last", singleArgRef().forOperator("$last"));
 		map.put("size", singleArgRef().forOperator("$size"));
 		map.put("slice", arrayArgRef().forOperator("$slice"));
+		map.put("sortArray", mapArgRef().forOperator("$sortArray").mappingParametersTo("input", "sortBy"));
 		map.put("reverseArray", singleArgRef().forOperator("$reverseArray"));
 		map.put("reduce", mapArgRef().forOperator("$reduce").mappingParametersTo("input", "initialValue", "in"));
 		map.put("zip", mapArgRef().forOperator("$zip").mappingParametersTo("inputs", "useLongestLength", "defaults"));

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

@@ -23,6 +23,7 @@
 
 import org.bson.Document;
 import org.junit.jupiter.api.Test;
+import org.springframework.data.domain.Sort;
 import org.springframework.data.mongodb.core.aggregation.ArrayOperators.ArrayToObject;
 
 /**
@@ -171,4 +172,11 @@ public void lastWithFieldReference() {
 		assertThat(ArrayOperators.arrayOf("field").last().toDocument(Aggregation.DEFAULT_CONTEXT))
 				.isEqualTo("{ $last : \"$field\" }");
 	}
+
+	@Test // GH-4139
+	void sortByWithFieldRef() {
+
+		assertThat(ArrayOperators.arrayOf("team").sort(Sort.by("name")).toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo("{ $sortArray: { input: \"$team\", sortBy: { name: 1 } } }");
+	}
 }

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

@@ -1235,6 +1235,12 @@ void shouldRenderSetField() {
 		assertThat(transform("setField(\"score\", 100, source)")).isEqualTo("{ $setField : { field : \"score\", value : 100, input : \"$source\" }}");
 	}
 
+	@Test // GH-4139
+	void shouldRenderSortArray() {
+		assertThat(transform(
+				"sortArray(team, new org.bson.Document(\"name\" , 1))")).isEqualTo("{ $sortArray : { input : \"$team\", sortBy : {\"name\" : 1 } }}");
+	}
+
 	private Document transform(String expression, Object... params) {
 		return (Document) transformer.transform(expression, Aggregation.DEFAULT_CONTEXT, params);
 	}