DATAMONGO-1538 - Add support for $let to $project aggregation.

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>1.10.0.BUILD-SNAPSHOT</version>
+	<version>1.10.0.DATAMONGO-1538-SNAPSHOT</version>
 	<packaging>pom</packaging>
 
 	<name>Spring Data MongoDB</name>

spring-data-mongodb-cross-store/pom.xml

@@ -6,7 +6,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>1.10.0.BUILD-SNAPSHOT</version>
+		<version>1.10.0.DATAMONGO-1538-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 
@@ -48,7 +48,7 @@
 		<dependency>
 			<groupId>org.springframework.data</groupId>
 			<artifactId>spring-data-mongodb</artifactId>
-			<version>1.10.0.BUILD-SNAPSHOT</version>
+			<version>1.10.0.DATAMONGO-1538-SNAPSHOT</version>
 		</dependency>
 
 		<dependency>

spring-data-mongodb-distribution/pom.xml

@@ -13,7 +13,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>1.10.0.BUILD-SNAPSHOT</version>
+		<version>1.10.0.DATAMONGO-1538-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb-log4j/pom.xml

@@ -5,7 +5,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>1.10.0.BUILD-SNAPSHOT</version>
+		<version>1.10.0.DATAMONGO-1538-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/pom.xml

@@ -11,7 +11,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>1.10.0.BUILD-SNAPSHOT</version>
+		<version>1.10.0.DATAMONGO-1538-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

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

@@ -17,6 +17,7 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -25,8 +26,8 @@
 import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.Cond.OtherwiseBuilder;
 import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.Cond.ThenBuilder;
 import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.Filter.AsBuilder;
+import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.Let.ExpressionVariable;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.ExposedField;
-import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldReference;
 import org.springframework.data.mongodb.core.query.CriteriaDefinition;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -1986,6 +1987,28 @@ public static Map.AsBuilder mapItemsOf(String fieldReference) {
 		public static Map.AsBuilder mapItemsOf(AggregationExpression expression) {
 			return Map.itemsOf(expression);
 		}
+
+		/**
+		 * Start creating new {@link Let} that allows definition of {@link ExpressionVariable} that can be used within a
+		 * nested {@link AggregationExpression}.
+		 *
+		 * @param variables must not be {@literal null}.
+		 * @return
+		 */
+		public static Let.LetBuilder define(ExpressionVariable... variables) {
+			return Let.define(variables);
+		}
+
+		/**
+		 * Start creating new {@link Let} that allows definition of {@link ExpressionVariable} that can be used within a
+		 * nested {@link AggregationExpression}.
+		 *
+		 * @param variables must not be {@literal null}.
+		 * @return
+		 */
+		public static Let.LetBuilder define(Collection<ExpressionVariable> variables) {
+			return Let.define(variables);
+		}
 	}
 
 	/**
@@ -3881,31 +3904,19 @@ public static AsBuilder filter(List<?> values) {
 		 */
 		@Override
 		public DBObject toDbObject(final AggregationOperationContext context) {
-
-			return toFilter(new ExposedFieldsAggregationOperationContext(ExposedFields.from(as), context) {
-
-				@Override
-				public FieldReference getReference(Field field) {
-
-					FieldReference ref = null;
-					try {
-						ref = context.getReference(field);
-					} catch (Exception e) {
-						// just ignore that one.
-					}
-					return ref != null ? ref : super.getReference(field);
-				}
-			});
+			return toFilter(ExposedFields.from(as), context);
 		}
 
-		private DBObject toFilter(AggregationOperationContext context) {
+		private DBObject toFilter(ExposedFields exposedFields, AggregationOperationContext context) {
 
 			DBObject filterExpression = new BasicDBObject();
+			InheritingExposedFieldsAggregationOperationContext operationContext = new InheritingExposedFieldsAggregationOperationContext(
+					exposedFields, context);
 
 			filterExpression.putAll(context.getMappedObject(new BasicDBObject("input", getMappedInput(context))));
 			filterExpression.put("as", as.getTarget());
 
-			filterExpression.putAll(context.getMappedObject(new BasicDBObject("cond", getMappedCondition(context))));
+			filterExpression.putAll(context.getMappedObject(new BasicDBObject("cond", getMappedCondition(operationContext))));
 
 			return new BasicDBObject("$filter", filterExpression);
 		}
@@ -5995,27 +6006,14 @@ public Map andApply(final AggregationExpression expression) {
 
 		@Override
 		public DBObject toDbObject(final AggregationOperationContext context) {
-
-			return toMap(new ExposedFieldsAggregationOperationContext(
-					ExposedFields.synthetic(Fields.fields(itemVariableName)), context) {
-
-				@Override
-				public FieldReference getReference(Field field) {
-
-					FieldReference ref = null;
-					try {
-						ref = context.getReference(field);
-					} catch (Exception e) {
-						// just ignore that one.
-					}
-					return ref != null ? ref : super.getReference(field);
-				}
-			});
+			return toMap(ExposedFields.synthetic(Fields.fields(itemVariableName)), context);
 		}
 
-		private DBObject toMap(AggregationOperationContext context) {
+		private DBObject toMap(ExposedFields exposedFields, AggregationOperationContext context) {
 
 			BasicDBObject map = new BasicDBObject();
+			InheritingExposedFieldsAggregationOperationContext operationContext = new InheritingExposedFieldsAggregationOperationContext(
+					exposedFields, context);
 
 			BasicDBObject input;
 			if (sourceArray instanceof Field) {
@@ -6026,7 +6024,8 @@ private DBObject toMap(AggregationOperationContext context) {
 
 			map.putAll(context.getMappedObject(input));
 			map.put("as", itemVariableName);
-			map.put("in", functionToApply.toDbObject(new NestedDelegatingExpressionAggregationOperationContext(context)));
+			map.put("in",
+					functionToApply.toDbObject(new NestedDelegatingExpressionAggregationOperationContext(operationContext)));
 
 			return new BasicDBObject("$map", map);
 		}
@@ -6696,4 +6695,173 @@ public Cond otherwiseValueOf(AggregationExpression expression) {
 			}
 		}
 	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $let} that binds {@link AggregationExpression} to variables for use in the
+	 * specified {@code in} expression, and returns the result of the expression.
+	 *
+	 * @author Christoph Strobl
+	 * @since 1.10
+	 */
+	class Let implements AggregationExpression {
+
+		private final List<ExpressionVariable> vars;
+		private final AggregationExpression expression;
+
+		private Let(List<ExpressionVariable> vars, AggregationExpression expression) {
+
+			this.vars = vars;
+			this.expression = expression;
+		}
+
+		/**
+		 * Start creating new {@link Let} by defining the variables for {@code $vars}.
+		 *
+		 * @param variables must not be {@literal null}.
+		 * @return
+		 */
+		public static LetBuilder define(final Collection<ExpressionVariable> variables) {
+
+			Assert.notNull(variables, "Variables must not be null!");
+
+			return new LetBuilder() {
+				@Override
+				public Let andApply(final AggregationExpression expression) {
+
+					Assert.notNull(expression, "Expression must not be null!");
+					return new Let(new ArrayList<ExpressionVariable>(variables), expression);
+				}
+			};
+		}
+
+		/**
+		 * Start creating new {@link Let} by defining the variables for {@code $vars}.
+		 *
+		 * @param variables must not be {@literal null}.
+		 * @return
+		 */
+		public static LetBuilder define(final ExpressionVariable... variables) {
+
+			Assert.notNull(variables, "Variables must not be null!");
+
+			return new LetBuilder() {
+				@Override
+				public Let andApply(final AggregationExpression expression) {
+
+					Assert.notNull(expression, "Expression must not be null!");
+					return new Let(Arrays.asList(variables), expression);
+				}
+			};
+		}
+
+		public interface LetBuilder {
+
+			/**
+			 * Define the {@link AggregationExpression} to evaluate.
+			 *
+			 * @param expression must not be {@literal null}.
+			 * @return
+			 */
+			Let andApply(AggregationExpression expression);
+		}
+
+		@Override
+		public DBObject toDbObject(final AggregationOperationContext context) {
+			return toLet(ExposedFields.synthetic(Fields.fields(getVariableNames())), context);
+		}
+
+		private String[] getVariableNames() {
+
+			String[] varNames = new String[this.vars.size()];
+			for (int i = 0; i < this.vars.size(); i++) {
+				varNames[i] = this.vars.get(i).variableName;
+			}
+
+			return varNames;
+		}
+
+		private DBObject toLet(ExposedFields exposedFields, AggregationOperationContext context) {
+
+			DBObject letExpression = new BasicDBObject();
+			DBObject mappedVars = new BasicDBObject();
+			InheritingExposedFieldsAggregationOperationContext operationContext = new InheritingExposedFieldsAggregationOperationContext(
+					exposedFields, context);
+
+			for (ExpressionVariable var : this.vars) {
+				mappedVars.putAll(getMappedVariable(var, context));
+			}
+
+			letExpression.put("vars", mappedVars);
+			letExpression.put("in", getMappedIn(operationContext));
+
+			return new BasicDBObject("$let", letExpression);
+		}
+
+		private DBObject getMappedVariable(ExpressionVariable var, AggregationOperationContext context) {
+
+			return new BasicDBObject(var.variableName, var.expression instanceof AggregationExpression
+					? ((AggregationExpression) var.expression).toDbObject(context) : var.expression);
+		}
+
+		private Object getMappedIn(AggregationOperationContext context) {
+			return expression.toDbObject(new NestedDelegatingExpressionAggregationOperationContext(context));
+		}
+
+		/**
+		 * @author Christoph Strobl
+		 */
+		public static class ExpressionVariable {
+
+			private final String variableName;
+			private final Object expression;
+
+			/**
+			 * Creates new {@link ExpressionVariable}.
+			 *
+			 * @param variableName can be {@literal null}.
+			 * @param expression can be {@literal null}.
+			 */
+			private ExpressionVariable(String variableName, Object expression) {
+
+				this.variableName = variableName;
+				this.expression = expression;
+			}
+
+			/**
+			 * Create a new {@link ExpressionVariable} with given name.
+			 *
+			 * @param variableName must not be {@literal null}.
+			 * @return never {@literal null}.
+			 */
+			public static ExpressionVariable newVariable(String variableName) {
+
+				Assert.notNull(variableName, "VariableName must not be null!");
+				return new ExpressionVariable(variableName, null);
+			}
+
+			/**
+			 * Create a new {@link ExpressionVariable} with current name and given {@literal expression}.
+			 *
+			 * @param expression must not be {@literal null}.
+			 * @return never {@literal null}.
+			 */
+			public ExpressionVariable forExpression(AggregationExpression expression) {
+
+				Assert.notNull(expression, "Expression must not be null!");
+				return new ExpressionVariable(variableName, expression);
+			}
+
+			/**
+			 * Create a new {@link ExpressionVariable} with current name and given {@literal expressionObject}.
+			 *
+			 * @param expressionObject must not be {@literal null}.
+			 * @return never {@literal null}.
+			 */
+			public ExpressionVariable forExpression(DBObject expressionObject) {
+
+				Assert.notNull(expressionObject, "Expression must not be null!");
+				return new ExpressionVariable(variableName, expressionObject);
+			}
+		}
+	}
 }

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

@@ -36,7 +36,7 @@
 @Deprecated
 public enum AggregationFunctionExpressions {
 
-	SIZE, CMP, EQ, GT, GTE, LT, LTE, NE, SUBTRACT, ADD;
+	SIZE, CMP, EQ, GT, GTE, LT, LTE, NE, SUBTRACT, ADD, MULTIPLY;
 
 	/**
 	 * Returns an {@link AggregationExpression} build from the current {@link Enum} name and the given parameters.

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

@@ -13,17 +13,16 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.mongodb.core.aggregation;
 
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldReference;
-import org.springframework.util.Assert;
 
 /**
  * {@link ExposedFieldsAggregationOperationContext} that inherits fields from its parent
  * {@link AggregationOperationContext}.
  *
  * @author Mark Paluch
+ * @since 1.9
  */
 class InheritingExposedFieldsAggregationOperationContext extends ExposedFieldsAggregationOperationContext {
 
@@ -40,7 +39,7 @@ public InheritingExposedFieldsAggregationOperationContext(ExposedFields exposedF
 			AggregationOperationContext previousContext) {
 
 		super(exposedFields, previousContext);
-		Assert.notNull(previousContext, "PreviousContext must not be null!");
+
 		this.previousContext = previousContext;
 	}