Merge pull request #70 from marklogic/feature/orderBy-multiple

Added test and docs example of multiple orderBy columns

Author: rjrudin

docs/reading.md

@@ -118,7 +118,7 @@ down the following operations to MarkLogic:
 - `filter` and `where`
 - `groupBy` when followed by `count`
 - `limit`
-- `orderBy`
+- `orderBy` and `sort`
 
 For each of the above operations, the user's Optic query is enhanced to include the associated Optic function.
 Note that if multiple partitions are used to perform the `read` operation, each
@@ -127,7 +127,42 @@ from each partition and re-apply the function calls as necessary to ensure that
 
 If either `count` or `groupBy` and `count` are pushed down, the connector will make a single request to MarkLogic to 
 resolve the query (thus ignoring the number of partitions and batch size that may have been configured; see below 
-for more information on these options), ensuring that a single count or set of counts is returned to Spark. 
+for more information on these options), ensuring that a single count or set of counts is returned to Spark.
+
+In the following example, every operation after `load()` is pushed down to MarkLogic, thereby resulting in far fewer 
+rows being returned to Spark and far less work having to be done by Spark:
+
+```
+spark.read.format("com.marklogic.spark") \
+    .option("spark.marklogic.client.uri", "spark-example-user:password@localhost:8020") \
+    .option("spark.marklogic.read.opticQuery", "op.fromView('example', 'employee', '')") \
+    .load() \
+    .filter("HiredDate < '2020-01-01'") \
+    .groupBy("State", "Department") \
+    .count() \
+    .orderBy("State", "count") \
+    .limit(10) \
+    .show()
+```
+
+The following results are returned:
+
+```
++-----+-----------+-----+                                                       
+|State| Department|count|
++-----+-----------+-----+
+|   AL|  Marketing|    1|
+|   AL|   Training|    1|
+|   AL|        R&D|    4|
+|   AL|      Sales|    4|
+|   AR|      Sales|    1|
+|   AR|  Marketing|    3|
+|   AR|        R&D|    9|
+|   AZ|   Training|    1|
+|   AZ|Engineering|    2|
+|   AZ|        R&D|    2|
++-----+-----------+-----+
+```
 
 ## Tuning performance
 

src/test/java/com/marklogic/spark/reader/PushDownOrderByAndLimitTest.java

@@ -188,6 +188,25 @@ void sort() {
         verifyRowsAreOrderedByCitationID(rows);
     }
 
+    @Test
+    void sortByMultiple() {
+        List<Row> rows = newDefaultReader()
+            .option(Options.READ_OPTIC_QUERY, QUERY_WITH_NO_QUALIFIER)
+            .load()
+            .sort("CitationID", "LastName")
+            .limit(8)
+            .collectAsList();
+
+        assertEquals(8, rows.size());
+        verifyRowsAreOrderedByCitationID(rows);
+
+        // Verify the first few rows to make sure they're sorted by LastName as well based on known values.
+        final String column = "LastName";
+        assertEquals("Awton", rows.get(0).getAs(column));
+        assertEquals("Bernadzki", rows.get(1).getAs(column));
+        assertEquals("Canham", rows.get(2).getAs(column));
+    }
+
     private void verifyRowsAreOrderedByCitationID(List<Row> rows) {
         // Lowest known CitationID is 1, so start comparisons against that.
         long previousValue = 1;