Merge pull request #6 from slyons/master

Optimized the column metadata lookup to happen just once. This greatly improves performance with larger bulk loads and larger number of partitions.

src/main/scala/com/microsoft/azure/sqldb/spark/connect/DataFrameFunctions.scala

@@ -31,6 +31,8 @@ import com.microsoft.azure.sqldb.spark.config.{Config, SqlDBConfig}
 import com.microsoft.sqlserver.jdbc.SQLServerBulkCopy
 import org.apache.spark.sql.{DataFrame, Row}
 
+import scala.util.Try
+
 /**
   * Implicit functions for DataFrame
   */
@@ -43,8 +45,45 @@ private[spark] case class DataFrameFunctions[T](@transient dataFrame: DataFrame)
     * @param config the database connection properties and bulk copy properties
     * @param metadata the metadata of the columns - will be null if not specified
     */
-  def bulkCopyToSqlDB(config: Config, metadata: BulkCopyMetadata = null): Unit = {
-    dataFrame.foreachPartition(iterator => bulkCopy(config, iterator, metadata))
+  def bulkCopyToSqlDB(config: Config, metadata: BulkCopyMetadata = null, createTable:Boolean = false): Unit = {
+    // Ensuring the table exists in the DB already
+    if(createTable) {
+      dataFrame.limit(0).write.sqlDB(config)
+    }
+
+    val actualMetadata = if(metadata == null) {
+      getConnectionOrFail(config).recover({
+        case e: ClassNotFoundException =>
+          logError("JDBC driver not found in class path", e)
+          throw e
+        case e1: SQLException =>
+          logError("Connection cannot be established to the database", e1)
+          throw e1
+      }).flatMap(conn => {
+        inferBulkCopyMetadata(config, conn)
+      }).recover({
+        case e: SQLException =>
+          logError("Column metadata not specified and cannot retrieve metadata from database", e)
+        throw e
+      }).get
+    } else {
+      metadata
+    }
+    dataFrame.foreachPartition(iterator => bulkCopy(config, iterator, actualMetadata))
+  }
+
+  private def getConnectionOrFail(config:Config):Try[Connection] = {
+    Try {
+      ConnectionUtils.getConnection(config)
+    }
+  }
+
+  private def inferBulkCopyMetadata(config: Config, connection:Connection):Try[BulkCopyMetadata] = {
+    val dbTable = config.get[String](SqlDBConfig.DBTable).get
+    Try {
+      val resultSetMetaData = BulkCopyUtils.getTableColumns(dbTable, connection)
+      BulkCopyUtils.createBulkCopyMetadata(resultSetMetaData)
+    }
   }
 
   /**
@@ -71,19 +110,7 @@ private[spark] case class DataFrameFunctions[T](@transient dataFrame: DataFrame)
     val dbTable = config.get[String](SqlDBConfig.DBTable).get
 
     // Retrieves column metadata from external database table if user does not specify.
-    val bulkCopyMetadata =
-      if (metadata != null) {
-        metadata
-      } else {
-        try {
-          val resultSetMetaData = BulkCopyUtils.getTableColumns(dbTable, connection)
-          BulkCopyUtils.createBulkCopyMetadata(resultSetMetaData)
-        } catch {
-          case e: SQLException =>
-            logError("Column metadata not specified and cannot retrieve metadata from database", e)
-            throw e
-        }
-      }
+    val bulkCopyMetadata = metadata
 
     var committed = false
     val supportsTransactions = BulkCopyUtils.getTransactionSupport(connection)