Fix N1qlExpression keys.

Fix syntax for USE KEYS [ ... ]

Closed #1064.
Original pull request: #1112.

Author: mikereiche

src/main/java/org/springframework/data/couchbase/core/query/N1QLExpression.java

@@ -262,13 +262,14 @@ public N1QLExpression returning(N1QLExpression right) {
 	public N1QLExpression keys(Iterable<? extends Serializable> ids) {
 		StringBuilder sb = new StringBuilder();
 		Iterator<?> it = ids.iterator();
-		// TODO: really? Lets do better.
+		sb.append("[");
 		while (it.hasNext()) {
-			sb.append(i(it.next().toString()));
+			sb.append(s(it.next().toString()));
 			if (it.hasNext()) {
 				sb.append(",");
 			}
 		}
+		sb.append("]");
 		return infix("USE KEYS", toString(), sb.toString());
 	}
 

src/test/java/org/springframework/data/couchbase/core/query/QueryCriteriaTests.java

@@ -28,6 +28,8 @@
 
 import com.couchbase.client.java.json.JsonArray;
 
+import java.util.Arrays;
+
 /**
  * @author Mauro Monti
  */
@@ -251,6 +253,15 @@ void testFalse() {
 		assertEquals("not( (`name`) )", c.export());
 	}
 
+	@Test
+	void testKeys() {
+		N1QLExpression expression = N1QLExpression.x("");
+		assertEquals(" USE KEYS [\"a\",\"b\"]", expression.keys(Arrays.asList("a", "b")).toString());
+		assertEquals(" USE KEYS [\"a\"]", expression.keys(Arrays.asList("a")).toString());
+		assertEquals(" USE KEYS []", expression.keys(Arrays.asList()).toString());
+	}
+
+
 	@Test // https://github.com/spring-projects/spring-data-couchbase/issues/1066
 	void testCriteriaCorrectlyEscapedWhenUsingMetaOnLHS() {
 		final String bucketName = "sample-bucket";