[SPARK-2334] fix AttributeError when call PipelineRDD.id()

The underline JavaRDD for PipelineRDD is created lazily, it's delayed until call _jrdd.

The id of JavaRDD is cached as `_id`, it saves a RPC call in py4j for later calls.

closes #1276

Author: Davies Liu <davies.liu@gmail.com>

Closes #2296 from davies/id and squashes the following commits:

e197958 [Davies Liu] fix style
9721716 [Davies Liu] fix id of PipelineRDD

python/pyspark/rdd.py

@@ -2075,6 +2075,7 @@ class PipelinedRDD(RDD):
         self.ctx = prev.ctx
         self.prev = prev
         self._jrdd_val = None
+        self._id = None
         self._jrdd_deserializer = self.ctx.serializer
         self._bypass_serializer = False
         self._partitionFunc = prev._partitionFunc if self.preservesPartitioning else None
@@ -2105,6 +2106,11 @@ class PipelinedRDD(RDD):
         self._jrdd_val = python_rdd.asJavaRDD()
         return self._jrdd_val
 
+    def id(self):
+        if self._id is None:
+            self._id = self._jrdd.id()
+        return self._id
+
     def _is_pipelinable(self):
         return not (self.is_cached or self.is_checkpointed)
 

python/pyspark/sql.py

@@ -1525,7 +1525,7 @@ class SchemaRDD(RDD):
         self.sql_ctx = sql_ctx
         self._sc = sql_ctx._sc
         self._jschema_rdd = jschema_rdd
-
+        self._id = None
         self.is_cached = False
         self.is_checkpointed = False
         self.ctx = self.sql_ctx._sc
@@ -1543,9 +1543,10 @@ class SchemaRDD(RDD):
             self._lazy_jrdd = self._jschema_rdd.javaToPython()
         return self._lazy_jrdd
 
-    @property
-    def _id(self):
-        return self._jrdd.id()
+    def id(self):
+        if self._id is None:
+            self._id = self._jrdd.id()
+        return self._id
 
     def saveAsParquetFile(self, path):
         """Save the contents as a Parquet file, preserving the schema.

python/pyspark/tests.py

@@ -281,6 +281,15 @@ class TestAddFile(PySparkTestCase):
 
 class TestRDDFunctions(PySparkTestCase):
 
+    def test_id(self):
+        rdd = self.sc.parallelize(range(10))
+        id = rdd.id()
+        self.assertEqual(id, rdd.id())
+        rdd2 = rdd.map(str).filter(bool)
+        id2 = rdd2.id()
+        self.assertEqual(id + 1, id2)
+        self.assertEqual(id2, rdd2.id())
+
     def test_failed_sparkcontext_creation(self):
         # Regression test for SPARK-1550
         self.sc.stop()