Add support for $expr operator

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

@@ -19,7 +19,13 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.bson.Document;
 import org.springframework.data.mongodb.core.aggregation.AddFieldsOperation.AddFieldsOperationBuilder.ValueAppender;
+import org.springframework.data.mongodb.core.aggregation.ExposedFields.ExposedField;
+import org.springframework.data.mongodb.core.aggregation.GroupOperation.Keyword;
+import org.springframework.data.mongodb.core.aggregation.GroupOperation.Operation;
+import org.springframework.data.mongodb.core.aggregation.ProjectionOperation.ProjectionOperationBuilder;
+
 import org.springframework.lang.Nullable;
 
 /**
@@ -123,14 +129,16 @@ private AddFieldsOperationBuilder() {
 		private AddFieldsOperationBuilder(Map<Object, Object> source) {
 			this.valueMap = new LinkedHashMap<>(source);
 		}
-
+		
 		public AddFieldsOperationBuilder addFieldWithValue(String field, @Nullable Object value) {
 			return addField(field).withValue(value);
 		}
 
 		public AddFieldsOperationBuilder addFieldWithValueOf(String field, Object value) {
 			return addField(field).withValueOf(value);
 		}
+
+
 
 		/**
 		 * Define the field to add.
@@ -168,7 +176,7 @@ public AddFieldsOperationBuilder withValueOfExpression(String operation, Object.
 		public AddFieldsOperation build() {
 			return new AddFieldsOperation(valueMap);
 		}
-
+		
 		/**
 		 * @author Christoph Strobl
 		 * @since 3.0
@@ -201,4 +209,6 @@ public interface ValueAppender {
 			AddFieldsOperationBuilder withValueOfExpression(String operation, Object... values);
 		}
 	}
+
+
 }

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

@@ -498,7 +498,17 @@ public static MatchOperation match(Criteria criteria) {
 	public static MatchOperation match(CriteriaDefinition criteria) {
 		return new MatchOperation(criteria);
 	}
-
+
+	/**
+	 * Creates a new {@link MatchOperation}
+	 *
+	 * @return new instance of {@link MatchOperation}.
+	 * @since 1.10
+	 */
+	public static MatchOperation match() {
+		return new MatchOperation();
+	}
+
 	/**
 	 * Creates a new {@link GeoNearOperation} instance from the given {@link NearQuery} and the {@code distanceField}. The
 	 * {@code distanceField} defines output field that contains the calculated distance.

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

@@ -0,0 +1,109 @@
+package org.springframework.data.mongodb.core.aggregation;
+
+import org.springframework.util.Assert;
+
+public class EvaluationOperators {
+
+	/**
+	 * Take the value resulting from the given fieldReference.
+	 *
+	 * @param fieldReference must not be {@literal null}.
+	 * @return new instance of {@link EvaluationOperatorFactory}.
+	 */
+	public static EvaluationOperatorFactory valueOf(String fieldReference) {
+		return new EvaluationOperatorFactory(fieldReference);
+	}
+
+	/**
+	 * Take the value resulting from the given {@link AggregationExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return new instance of {@link EvaluationOperatorFactory}.
+	 */
+	public static EvaluationOperatorFactory valueOf(AggregationExpression expression) {
+		return new EvaluationOperatorFactory(expression);
+	}
+
+	public static class EvaluationOperatorFactory {
+
+		private final String fieldReference;
+		private final AggregationExpression expression;
+
+		/**
+		 * Creates new {@link EvaluationOperatorFactory} for given {@literal fieldReference}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 */
+		public EvaluationOperatorFactory(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			this.fieldReference = fieldReference;
+			this.expression = null;
+		}
+
+
+		/**
+		 * Creates new {@link EvaluationOperatorFactory} for given {@link AggregationExpression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 */
+		public EvaluationOperatorFactory(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+			this.fieldReference = null;
+			this.expression = expression;
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that is a valid aggregation expression.
+		 *
+		 * @return new instance of {@link Expr}.
+		 */
+		public Expr expr() {
+			return usesFieldRef() ? Expr.valueOf(fieldReference) : Expr.valueOf(expression);
+		}
+
+
+		public static class Expr extends AbstractAggregationExpression {
+
+			private Expr(Object value) {
+				super(value);
+			}
+
+			@Override
+			protected String getMongoMethod() {
+				return "$expr";
+			}
+
+			/**
+			 * Creates new {@link Expr}.
+			 *
+			 * @param fieldReference must not be {@literal null}.
+			 * @return new instance of {@link Expr}.
+			 */
+			public static Expr valueOf(String fieldReference) {
+
+				Assert.notNull(fieldReference, "FieldReference must not be null!");
+				return new Expr(Fields.field(fieldReference));
+			}
+
+			/**
+			 * Creates new {@link Expr}.
+			 *
+			 * @param expression must not be {@literal null}.
+			 * @return new instance of {@link Expr}.
+			 */
+			public static Expr valueOf(AggregationExpression expression) {
+
+				Assert.notNull(expression, "Expression must not be null!");
+				return new Expr(expression);
+			}
+
+		}
+
+		private boolean usesFieldRef() {
+			return fieldReference != null;
+		}
+	}
+
+}

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

@@ -16,6 +16,7 @@
 package org.springframework.data.mongodb.core.aggregation;
 
 import org.bson.Document;
+import org.springframework.data.mongodb.core.aggregation.EvaluationOperators.EvaluationOperatorFactory.Expr;
 import org.springframework.data.mongodb.core.query.CriteriaDefinition;
 import org.springframework.util.Assert;
 
@@ -36,7 +37,16 @@
 public class MatchOperation implements AggregationOperation {
 
 	private final CriteriaDefinition criteriaDefinition;
-
+	private final AggregationExpression expression;
+
+	/**
+	 * Creates a new {@link MatchOperation}
+	 */
+	public MatchOperation() {
+		this.criteriaDefinition = null;
+		this.expression = null;
+	}
+
 	/**
 	 * Creates a new {@link MatchOperation} for the given {@link CriteriaDefinition}.
 	 *
@@ -46,14 +56,39 @@ public MatchOperation(CriteriaDefinition criteriaDefinition) {
 
 		Assert.notNull(criteriaDefinition, "Criteria must not be null!");
 		this.criteriaDefinition = criteriaDefinition;
+		this.expression = null;
 	}
-
+
+	/**
+	 * Creates a new {@link MatchOperation} for the given {@link Expression}.
+	 *
+	 * @param criteriaDefinition must not be {@literal null}.
+	 */
+	private MatchOperation(Expr expression) {
+		Assert.notNull(expression, "Expression must not be null!");
+		this.criteriaDefinition = null;
+		this.expression = expression;
+	}
+
+	/**
+	 * Creates a new {@link MatchOperation} for the given {@link AggregationExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 */
+	public MatchOperation withValueOf(AggregationExpression expression) {
+		Assert.notNull(expression, "Expression must not be null!");
+		return new MatchOperation(EvaluationOperators.valueOf(expression).expr());
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#toDocument(org.springframework.data.mongodb.core.aggregation.AggregationOperationContext)
 	 */
 	@Override
 	public Document toDocument(AggregationOperationContext context) {
+		if(expression != null) {
+			return new Document(getOperator(), expression.toDocument());
+		}
 		return new Document(getOperator(), context.getMappedObject(criteriaDefinition.getCriteriaObject()));
 	}
 

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

@@ -1306,7 +1306,7 @@ public ProjectionOperationBuilder let(AggregationExpression valueExpression, Str
 		public ProjectionOperationBuilder let(Collection<ExpressionVariable> variables, AggregationExpression in) {
 			return this.operation.and(VariableOperators.Let.define(variables).andApply(in));
 		}
-
+		
 		private String getRequiredName() {
 
 			Assert.state(name != null, "Projection field name must not be null!");

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

@@ -21,6 +21,7 @@
 import java.util.List;
 
 import org.bson.Document;
+import org.springframework.data.mongodb.core.aggregation.AddFieldsOperation.AddFieldsOperationBuilder;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.ExposedField;
 import org.springframework.expression.spel.ast.Projection;
 import org.springframework.util.Assert;
@@ -112,7 +113,8 @@ public ExposedFields getFields() {
 	protected Replacement getReplacement() {
 		return replacement;
 	}
-
+
+
 	/**
 	 * Builder for {@link ReplaceRootOperation}.
 	 *

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

@@ -19,6 +19,7 @@
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.springframework.data.mongodb.core.aggregation.AddFieldsOperation.AddFieldsOperationBuilder;
 import org.springframework.data.mongodb.core.aggregation.SetOperation.FieldAppender.ValueAppender;
 import org.springframework.lang.Nullable;
 
@@ -193,5 +194,7 @@ public interface ValueAppender {
 			 */
 			SetOperation withValueOfExpression(String operation, Object... values);
 		}
+
+
 	}
 }

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

@@ -126,6 +126,23 @@ void exposesFieldsCorrectly() {
 		assertThat(fields.getField("computed")).isNotNull();
 		assertThat(fields.getField("does-not-exist")).isNull();
 	}
+
+	@Test // DATAMONGO - 3729
+	void rendersStdDevPopCorrectly() {
+		assertThat(AddFieldsOperation.builder().addField("totalQuiz")
+				.withValue(ArithmeticOperators.valueOf("quiz").stdDevPop()).build()
+				.toPipelineStages(contextFor(ScoresWrapper.class))).containsExactly(
+						Document.parse("{\"$addFields\" : {\"totalQuiz\": { \"$stdDevPop\" : \"$quiz\" } }}"));
+	}
+
+	@Test // DATAMONGO - 3729
+	void rendersStdDevSampCorrectly() {
+		assertThat(AddFieldsOperation.builder().addField("totalQuiz")
+				.withValue(ArithmeticOperators.valueOf("quiz").stdDevSamp()).build()
+		.toPipelineStages(contextFor(ScoresWrapper.class)))
+					.containsExactly(Document.parse(
+							"{\"$addFields\" : {\"totalQuiz\": { \"$stdDevSamp\" : \"$quiz\" } }}"));
+	}
 
 	private static AggregationOperationContext contextFor(@Nullable Class<?> type) {
 

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

@@ -133,6 +133,7 @@ void unwindOperationWithPreserveNullShouldBuildCorrectClause() {
 				.doesNotContainKey("$unwind.includeArrayIndex") //
 				.containsEntry("$unwind.preserveNullAndEmptyArrays", true);
 	}
+
 
 	@Test // DATAMONGO-1550
 	void replaceRootOperationShouldBuildCorrectClause() {
@@ -145,7 +146,7 @@ void replaceRootOperationShouldBuildCorrectClause() {
 		Document unwind = ((List<Document>) agg.get("pipeline")).get(0);
 		assertThat(unwind).containsEntry("$replaceRoot.newRoot", new Document("field", "value"));
 	}
-
+		
 	@Test // DATAMONGO-753
 	void matchOperationShouldNotChangeAvailableFields() {
 
@@ -155,7 +156,7 @@ void matchOperationShouldNotChangeAvailableFields() {
 				project("a", "b") // b should still be available
 		).toDocument("foo", Aggregation.DEFAULT_CONTEXT);
 	}
-
+	
 	@Test // DATAMONGO-788
 	void referencesToGroupIdsShouldBeRenderedAsReferences() {
 
@@ -597,7 +598,7 @@ void projectOnIdIsAlwaysValid() {
 
 		assertThat(extractPipelineElement(target, 1, "$project")).isEqualTo(Document.parse(" { \"_id\" : \"$_id\" }"));
 	}
-
+		
 	private Document extractPipelineElement(Document agg, int index, String operation) {
 
 		List<Document> pipeline = (List<Document>) agg.get("pipeline");

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

@@ -0,0 +1,26 @@
+package org.springframework.data.mongodb.core.aggregation;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.bson.Document;
+import org.junit.jupiter.api.Test;
+
+class MatchOperationUnitTests {
+
+	@Test // DATAMONGO - 3729
+	public void shouldRenderStdDevPopCorrectly() {
+		MatchOperation operation = Aggregation.match().withValueOf(ArithmeticOperators.valueOf("quiz").stdDevPop());
+		assertThat(operation.toDocument(Aggregation.DEFAULT_CONTEXT)).
+			isEqualTo(Document.parse("{ $match: { \"$expr\" : { \"$stdDevPop\" : \"$quiz\" } } } "));
+
+	}
+
+	@Test // DATAMONGO - 3729
+	public void shouldRenderStdDevSampCorrectly() {
+		MatchOperation operation = Aggregation.match().withValueOf(ArithmeticOperators.valueOf("quiz").stdDevSamp());
+		assertThat(operation.toDocument(Aggregation.DEFAULT_CONTEXT)).
+			isEqualTo(Document.parse("{ $match: { \"$expr\" : { \"$stdDevSamp\" : \"$quiz\" } } } "));
+
+	}
+
+}