Fixes, added currentAsMap

Author: katcharov

driver-core/src/main/com/mongodb/client/model/expressions/Expressions.java

@@ -177,6 +177,19 @@ public static <R extends DocumentExpression> R current() {
                 .assertImplementsAllExpressions();
     }
 
+    /**
+     * Returns the "current" value as a {@linkplain MapExpression map} value.
+     * The "current" value is the top-level document currently being processed
+     * in the aggregation pipeline stage.
+     *
+     * @return the resulting value
+     * @param <R> the type of the resulting value
+     */
+    public static <R extends Expression> MapExpression<R> currentAsMap() {
+        return new MqlExpression<>((cr) -> new AstPlaceholder(new BsonString("$$CURRENT")))
+                .assertImplementsAllExpressions();
+    }
+
     @SafeVarargs  // nothing is stored in the array
     public static <T extends Expression> ArrayExpression<T> ofArray(final T... array) {
         Assertions.notNull("array", array);

driver-sync/src/test/functional/com/mongodb/client/model/expressions/InContextExpressionsFunctionalTest.java

@@ -18,6 +18,7 @@
 
 import com.mongodb.MongoClientSettings;
 import com.mongodb.client.AggregateIterable;
+import com.mongodb.client.FindIterable;
 import com.mongodb.client.MongoClient;
 import com.mongodb.client.MongoClients;
 import com.mongodb.client.MongoCollection;
@@ -36,14 +37,13 @@
 import static com.mongodb.client.model.Accumulators.sum;
 import static com.mongodb.client.model.Aggregates.match;
 import static com.mongodb.client.model.Aggregates.project;
+import static com.mongodb.client.model.Filters.expr;
 import static com.mongodb.client.model.Projections.computed;
 import static com.mongodb.client.model.Projections.excludeId;
 import static com.mongodb.client.model.Projections.fields;
 import static com.mongodb.client.model.Projections.include;
 import static com.mongodb.client.model.Sorts.ascending;
-import static com.mongodb.client.model.expressions.Expressions.current;
-import static com.mongodb.client.model.expressions.Expressions.of;
-import static com.mongodb.client.model.expressions.Expressions.ofArray;
+import static com.mongodb.client.model.expressions.Expressions.*;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class InContextExpressionsFunctionalTest extends AbstractExpressionsFunctionalTest {
@@ -63,7 +63,7 @@ public void tearDown() {
         client.close();
     }
 
-    private String bsonToString(final Bson project) {
+    private static String bsonToString(final Bson project) {
         return project.toBsonDocument(Document.class, MongoClientSettings.getDefaultCodecRegistry()).toString().replaceAll("\"", "'");
     }
 
@@ -74,6 +74,23 @@ private List<Document> aggregate(final Bson... stages) {
         return results;
     }
 
+    @Test
+    public void findTest() {
+        col.insertMany(Arrays.asList(
+                Document.parse("{_id: 1, x: 0, y: 2}"),
+                Document.parse("{_id: 2, x: 0, y: 3}"),
+                Document.parse("{_id: 3, x: 1, y: 3}")));
+
+        FindIterable<Document> iterable = col.find(expr(
+                current().getInteger("x").eq(of(1))));
+        List<Document> results = new ArrayList<>();
+        iterable.forEach(r -> results.add(r));
+
+        assertEquals(
+                Arrays.asList(Document.parse("{_id: 3, x: 1, y: 3}")),
+                results);
+    }
+
     @Test
     public void matchTest() {
         col.insertMany(Arrays.asList(
@@ -82,7 +99,25 @@ public void matchTest() {
                 Document.parse("{_id: 3, x: 1, y: 3}")));
 
         List<Document> results = aggregate(
-                match(Filters.expr(current().getInteger("x").eq(of(1)))));
+                match(expr(current().getInteger("x").eq(of(1)))));
+
+        assertEquals(
+                Arrays.asList(Document.parse("{_id: 3, x: 1, y: 3}")),
+                results);
+    }
+
+    @Test
+    public void currentAsMapMatchTest() {
+        col.insertMany(Arrays.asList(
+                Document.parse("{_id: 1, x: 0, y: 2}"),
+                Document.parse("{_id: 2, x: 0, y: 3}"),
+                Document.parse("{_id: 3, x: 1, y: 3}")));
+
+        List<Document> results = aggregate(
+                match(expr(Expressions.<NumberExpression>currentAsMap()
+                        .entrySet()
+                        .map(e -> e.getValue())
+                        .sum(v -> v).eq(of(7)))));
 
         assertEquals(
                 Arrays.asList(Document.parse("{_id: 3, x: 1, y: 3}")),
@@ -131,8 +166,8 @@ public void projectTest2() {
 
         // new, document
         Bson projectDocument = project(fields(computed("nested",
-                //BsonDocument.parse("{ x: {$max : ['$x', 4] }}")
-                of(new Document()).setField("x", current().getInteger("x").max(of(4)))
+                // the below is roughly: "{ x: {$max : ['$x', 4] }}"
+                of(Document.parse("{x: 9}")).setField("x", current().getInteger("x").max(of(4)))
         )));
         assertEquals(
                 Arrays.asList(Document.parse("{_id: 0, nested: { x: 4 } }")),