DATAMONGO-1536 - Add literal operators (aggregation).

Author: christophstrobl

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

@@ -870,6 +870,42 @@ private boolean usesFieldRef() {
 		}
 	}
 
+	/**
+	 * @author Christoph Strobl
+	 */
+	class LiteralOperators {
+
+		/**
+		 * Take the value referenced by given {@literal value}.
+		 *
+		 * @param value must not be {@literal null}.
+		 * @return
+		 */
+		public static LiteralOperatorFactory valueOf(Object value) {
+
+			Assert.notNull(value, "Value must not be null!");
+			return new LiteralOperatorFactory(value);
+		}
+
+		public static class LiteralOperatorFactory {
+
+			private final Object value;
+
+			public LiteralOperatorFactory(Object value) {
+				this.value = value;
+			}
+
+			/**
+			 * Returns the associated value without parsing.
+			 *
+			 * @return
+			 */
+			public Literal asLiteral() {
+				return Literal.asLiteral(value);
+			}
+		}
+	}
+
 	/**
 	 * @author Christoph Strobl
 	 */
@@ -2253,4 +2289,25 @@ public interface SliceElementsBuilder {
 		}
 	}
 
+	/**
+	 * {@link AggregationExpression} for {@code $literal}.
+	 *
+	 * @author Christoph Strobl
+	 */
+	class Literal extends AbstractAggregationExpression {
+
+		private Literal(Object value) {
+			super(value);
+		}
+
+		@Override
+		public String getMongoMethod() {
+			return "$literal";
+		}
+
+		public static Literal asLiteral(Object value) {
+			return new Literal(value);
+		}
+	}
+
 }

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

@@ -1131,7 +1131,7 @@ public ProjectionOperationBuilder strCaseCmp(AggregationExpression expression) {
 		 * @return
 		 * @since 1.10
 		 */
-		ProjectionOperationBuilder arrayElementAt(int position) {
+		public ProjectionOperationBuilder arrayElementAt(int position) {
 			return project("arrayElemAt", position);
 		}
 
@@ -1143,7 +1143,7 @@ ProjectionOperationBuilder arrayElementAt(int position) {
 		 * @return
 		 * @since 1.10
 		 */
-		ProjectionOperationBuilder concatArrays(String... fields) {
+		public ProjectionOperationBuilder concatArrays(String... fields) {
 			return project("concatArrays", Fields.fields(fields));
 		}
 
@@ -1153,10 +1153,20 @@ ProjectionOperationBuilder concatArrays(String... fields) {
 		 * @return
 		 * @since 1.10
 		 */
-		ProjectionOperationBuilder isArray() {
+		public ProjectionOperationBuilder isArray() {
 			return this.operation.and(AggregationExpressions.IsArray.isArray(name));
 		}
 
+		/**
+		 * Takes the value previously and uses it as literal.
+		 *
+		 * @return
+		 * @since 1.10
+		 */
+		public ProjectionOperationBuilder asLiteral() {
+			return this.operation.and(AggregationExpressions.Literal.asLiteral(name));
+		}
+
 		/* 
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#toDBObject(org.springframework.data.mongodb.core.aggregation.AggregationOperationContext)
@@ -1345,7 +1355,7 @@ protected List<Object> getOperationArguments(AggregationOperationContext context
 					if (element instanceof Field) {
 						result.add(context.getReference((Field) element).toString());
 					} else if (element instanceof Fields) {
-						for(Field field : (Fields)element) {
+						for (Field field : (Fields) element) {
 							result.add(context.getReference(field).toString());
 						}
 					} else if (element instanceof AggregationExpression) {

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

@@ -30,6 +30,7 @@
 import org.springframework.data.mongodb.core.DBObjectTestUtils;
 import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.ArithmeticOperators;
 import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.ArrayOperators;
+import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.LiteralOperators;
 import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.SetOperators;
 import org.springframework.data.mongodb.core.aggregation.AggregationExpressions.StringOperators;
 import org.springframework.data.mongodb.core.aggregation.ProjectionOperation.ProjectionOperationBuilder;
@@ -1254,6 +1255,29 @@ public void shouldRenderSliceWithPositionAggregationExpression() {
 		assertThat(agg, is(JSON.parse("{ $project: { threeFavorites: { $slice: [ \"$favorites\", 2, 3 ] } } }")));
 	}
 
+	/**
+	 * @see DATAMONGO-1536
+	 */
+	@Test
+	public void shouldRenderLiteral() {
+
+		DBObject agg = project().and("$1").asLiteral().as("literalOnly").toDBObject(Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(agg, is(JSON.parse("{ $project: { literalOnly: { $literal:  \"$1\"} } }")));
+	}
+
+	/**
+	 * @see DATAMONGO-1536
+	 */
+	@Test
+	public void shouldRenderLiteralAggregationExpression() {
+
+		DBObject agg = project().and(LiteralOperators.valueOf("$1").asLiteral()).as("literalOnly")
+				.toDBObject(Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(agg, is(JSON.parse("{ $project: { literalOnly: { $literal:  \"$1\"} } }")));
+	}
+
 	private static DBObject exctractOperation(String field, DBObject fromProjectClause) {
 		return (DBObject) fromProjectClause.get(field);
 	}