[SPARK-15804][SQL]Include metadata in the toStructType

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/package.scala

@@ -91,7 +91,7 @@ package object expressions  {
   implicit class AttributeSeq(val attrs: Seq[Attribute]) extends Serializable {
     /** Creates a StructType with a schema matching this `Seq[Attribute]`. */
     def toStructType: StructType = {
-      StructType(attrs.map(a => StructField(a.name, a.dataType, a.nullable)))
+      StructType(attrs.map(a => StructField(a.name, a.dataType, a.nullable, a.metadata)))
     }
 
     // It's possible that `attrs` is a linked list, which can lead to bad O(n^2) loops when

sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetQuerySuite.scala

@@ -625,6 +625,21 @@ class ParquetQuerySuite extends QueryTest with ParquetTest with SharedSQLContext
       }
     }
   }
+
+  test("SPARK-15804: write out the metadata to parquet file") {
+    val df = Seq((1, "abc"), (2, "hello")).toDF("a", "b")
+    val md = new MetadataBuilder().putString("key", "value").build()
+    val dfWithmeta = df.select('a, 'b.as("b", md))
+
+    withTempPath { dir =>
+      val path = dir.getCanonicalPath
+      dfWithmeta.write.parquet(path)
+
+      readParquetFile(path) { df =>
+        assert(df.schema.last.metadata.getString("key") == "value")
+      }
+    }
+  }
 }
 
 object TestingUDT {