Add support for $setField aggregation operator.

See #4139
Original pull request: #4182.

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

@@ -18,8 +18,10 @@ package org.springframework.data.mongodb.core.aggregation;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Set;
 
 import org.bson.Document;
+import org.springframework.data.mongodb.core.aggregation.Aggregation.SystemVariable;
 import org.springframework.util.Assert;
 
 /**
@@ -135,6 +137,26 @@ public class ObjectOperators {
 		public GetField getField(String fieldName) {
 			return GetField.getField(fieldName).from(value);
 		}
+
+		/**
+		 * Creates new {@link SetField aggregation expression} that takes the associated value and obtains the value of the
+		 * field with matching name.
+		 *
+		 * @since 4.0
+		 */
+		public SetField setField(String fieldName) {
+			return SetField.setField(fieldName).of(value);
+		}
+
+		/**
+		 * Creates new {@link SetField aggregation expression} that takes the associated value and obtains the value of the
+		 * field with matching name.
+		 *
+		 * @since 4.0
+		 */
+		public AggregationExpression removeField(String fieldName) {
+			return SetField.setField(fieldName).of(value).toValue(SystemVariable.REMOVE);
+		}
 	}
 
 	/**
@@ -332,4 +354,54 @@ public class ObjectOperators {
 			return "$getField";
 		}
 	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $setField}.
+	 *
+	 * @author Christoph Strobl
+	 * @since 4.0
+	 */
+	public static class SetField extends AbstractAggregationExpression {
+
+		protected SetField(Object value) {
+			super(value);
+		}
+
+		public static SetField setField(String fieldName) {
+			return new SetField(Collections.singletonMap("field", fieldName));
+		}
+
+		public static SetField setField(Field field) {
+			return setField(field.getTarget());
+		}
+
+		public SetField of(String fieldRef) {
+			return of(Fields.field(fieldRef));
+		}
+
+		public SetField of(AggregationExpression expression) {
+			return of((Object) expression);
+		}
+
+		private SetField of(Object fieldRef) {
+			return new SetField(append("input", fieldRef));
+		}
+
+		public SetField toValueOf(String fieldReference) {
+			return toValue(Fields.field(fieldReference));
+		}
+
+		public SetField toValueOf(AggregationExpression expression) {
+			return toValue(expression);
+		}
+
+		public SetField toValue(Object value) {
+			return new SetField(append("value", value));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$setField";
+		}
+	}
 }

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

@@ -233,6 +233,7 @@ public class MethodReferenceNode extends ExpressionNode {
 		map.put("objectToArray", singleArgRef().forOperator("$objectToArray"));
 		map.put("mergeObjects", arrayArgRef().forOperator("$mergeObjects"));
 		map.put("getField", mapArgRef().forOperator("$getField").mappingParametersTo("field", "input"));
+		map.put("setField", mapArgRef().forOperator("$setField").mappingParametersTo("field", "value", "input"));
 
 		// CONVERT OPERATORS
 		map.put("convert", mapArgRef().forOperator("$convert") //

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

@@ -109,4 +109,18 @@ public class ObjectOperatorsUnitTests {
 				.isEqualTo(Document.parse("{ $getField : { field : \"robin\", input : \"$batman\" }}"));
 	}
 
+	@Test // GH-4139
+	public void setField() {
+
+		assertThat(ObjectOperators.valueOf("batman").setField("friend").toValue("robin").toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $setField : { field : \"friend\", value : \"robin\", input : \"$batman\" }}"));
+	}
+
+	@Test // GH-4139
+	public void removeField() {
+
+		assertThat(ObjectOperators.valueOf("batman").removeField("joker").toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(Document.parse("{ $setField : { field : \"joker\", value : \"$$REMOVE\", input : \"$batman\" }}"));
+	}
+
 }

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

@@ -1230,6 +1230,11 @@ public class SpelExpressionTransformerUnitTests {
 		assertThat(transform("getField(\"score\", source)")).isEqualTo("{ $getField : { field : \"score\", input : \"$source\" }}");
 	}
 
+	@Test // GH-4139
+	void shouldRenderSetField() {
+		assertThat(transform("setField(\"score\", 100, source)")).isEqualTo("{ $setField : { field : \"score\", value : 100, input : \"$source\" }}");
+	}
+
 	private Document transform(String expression, Object... params) {
 		return (Document) transformer.transform(expression, Aggregation.DEFAULT_CONTEXT, params);
 	}