[GitHub] [spark] amaliujia commented on a diff in pull request #36969: [SPARK-39235][SQL] make setCurrentDatabase compatible with 3 layer namespace

[GitBox <gi...@apache.org>]

amaliujia commented on code in PR #36969:
URL: https://github.com/apache/spark/pull/36969#discussion_r905474007


##########
sql/core/src/main/scala/org/apache/spark/sql/internal/CatalogImpl.scala:
##########
@@ -43,30 +43,47 @@ class CatalogImpl(sparkSession: SparkSession) extends Catalog {
 
   private def sessionCatalog: SessionCatalog = sparkSession.sessionState.catalog
 
-  private def requireDatabaseExists(dbName: String): Unit = {
-    if (!sessionCatalog.databaseExists(dbName)) {
-      throw QueryCompilationErrors.databaseDoesNotExistError(dbName)
-    }
-  }
-
   private def requireTableExists(dbName: String, tableName: String): Unit = {
     if (!sessionCatalog.tableExists(TableIdentifier(tableName, Some(dbName)))) {
       throw QueryCompilationErrors.tableDoesNotExistInDatabaseError(tableName, dbName)
     }
   }
 
+  // FIXME
+  private var currentDatabaseV2: Option[String] = None
+
   /**
    * Returns the current default database in this session.
    */
-  override def currentDatabase: String = sessionCatalog.getCurrentDatabase
+  override def currentDatabase: String =
+    currentDatabaseV2.getOrElse(sessionCatalog.getCurrentDatabase)
 
   /**
    * Sets the current default database in this session.
    */
   @throws[AnalysisException]("database does not exist")
   override def setCurrentDatabase(dbName: String): Unit = {
-    requireDatabaseExists(dbName)
-    sessionCatalog.setCurrentDatabase(dbName)
+    // `dbName` could be either a single database name (behavior in Spark 3.3 and prior) or
+    // a qualified namespace with catalog name. We assume it's a single database name
+    // and check if we can find the dbName in sessionCatalog. If so, we set the use old
+    // sessionCatalog APIs to set current database. Otherwise, we try 3-part name parsing and
+    // check if the database exists with catalogV2 APIs
+    if (sessionCatalog.databaseExists(dbName)) {

Review Comment:
   Probably no need to do all of this.
   
   You can use https://github.com/apache/spark/blob/a3fdf3b107b62089890a4246c168ca516dff5d44/sql/catalyst/src/main/scala/org/apache/spark/sql/connector/catalog/CatalogManager.scala#L106.
   
   You can access the catalog manager by `sparkSession.sessionState.catalogManager`



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