#21: Added warning when tables scan result is empty. (#24)

pom.xml

@@ -9,7 +9,7 @@
     <description>Common module for JDBC-based data access from Virtual Schemas.</description>
     <url>https://github.com/exasol/virtual-schema-common-jdbc</url>
     <properties>
-        <product.version>2.2.0</product.version>
+        <product.version>2.2.1</product.version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <java.version>11</java.version>

src/main/java/com/exasol/adapter/jdbc/AbstractRemoteMetadataReader.java

@@ -110,7 +110,7 @@ private List<TableMetadata> extractTableMetadata(final DatabaseMetaData remoteMe
         logTablesScan(catalogName, schemaName);
         try (final ResultSet remoteTables = remoteMetadata.getTables(catalogName, schemaName, ANY_TABLE,
                 getTableTypeFilter())) {
-            return mapTables(remoteTables, selectedTables);
+            return this.tableMetadataReader.mapTables(remoteTables, selectedTables);
         }
     }
 
@@ -149,11 +149,6 @@ protected void logTablesScan(final String catalogName, final String schemaName)
         });
     }
 
-    private List<TableMetadata> mapTables(final ResultSet remoteTables, final Optional<List<String>> selectedTables)
-            throws SQLException {
-        return this.tableMetadataReader.mapTables(remoteTables, selectedTables);
-    }
-
     @Override
     public SchemaAdapterNotes getSchemaAdapterNotes() {
         try {

src/main/java/com/exasol/adapter/jdbc/BaseTableMetadataReader.java

@@ -41,8 +41,16 @@ public BaseTableMetadataReader(final Connection connection, final ColumnMetadata
     public List<TableMetadata> mapTables(final ResultSet remoteTables, final Optional<List<String>> selectedTables)
             throws SQLException {
         final List<TableMetadata> translatedTables = new ArrayList<>();
-        while (remoteTables.next()) {
-            mapOrSkipTable(remoteTables, translatedTables, selectedTables);
+        if (remoteTables.next()) {
+            do {
+                mapOrSkipTable(remoteTables, translatedTables, selectedTables);
+            } while (remoteTables.next());
+        } else {
+            LOGGER.warning(() -> "Table scan did not find any tables. This can mean that either" //
+                    + " a) the source does not contain tables (yet)," + " b) the table type is not supported or" //
+                    + " c) the table scan filter criteria is incorrect." //
+                    + " Please check that the source actually contains tables. " //
+                    + " Also check the spelling and exact case of any catalog or schema name you provided.");
         }
         return translatedTables;
     }
@@ -57,8 +65,8 @@ protected void mapOrSkipTable(final ResultSet remoteTables, final List<TableMeta
         }
     }
 
-    private void mapSupportedTables(ResultSet remoteTables, List<TableMetadata> translatedTables,
-            Optional<List<String>> selectedTables, String tableName) throws SQLException {
+    private void mapSupportedTables(final ResultSet remoteTables, final List<TableMetadata> translatedTables,
+            final Optional<List<String>> selectedTables, final String tableName) throws SQLException {
         if (isTableSelected(tableName, selectedTables)) {
             mapOrSkipSelectedTable(remoteTables, translatedTables, tableName);
         } else {
@@ -85,7 +93,7 @@ protected void mapOrSkipSelectedTable(final ResultSet remoteTables, final List<T
     }
 
     private boolean isTableFilteredOut(final String tableName) {
-        List<String> filteredTables = this.properties.getFilteredTables();
+        final List<String> filteredTables = this.properties.getFilteredTables();
         if (filteredTables.isEmpty()) {
             return false;
         } else {

src/test/java/com/exasol/adapter/jdbc/AbstractRemoteMetadataReaderTest.java

@@ -1,6 +1,7 @@
 package com.exasol.adapter.jdbc;
 
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.when;
 
 import java.sql.Connection;
 import java.sql.SQLException;
@@ -22,7 +23,7 @@ void testGetSchemaAdapterNotesWithSqlException() throws SQLException {
 
     private Connection mockConnectionThrowingExceptionOnGetMetadata() throws SQLException {
         final Connection connectionMock = Mockito.mock(Connection.class);
-        Mockito.when(connectionMock.getMetaData()).thenThrow(new SQLException("FAKE SQL exception"));
+        when(connectionMock.getMetaData()).thenThrow(new SQLException("FAKE SQL exception"));
         return connectionMock;
     }
 

src/test/java/com/exasol/adapter/jdbc/BaseTableMetadataReaderTest.java

@@ -1,15 +1,15 @@
 package com.exasol.adapter.jdbc;
 
 import static com.exasol.adapter.jdbc.TableMetadataMockUtils.*;
-import static org.hamcrest.Matchers.equalTo;
-import static org.hamcrest.Matchers.iterableWithSize;
+import static org.hamcrest.Matchers.*;
 import static org.junit.Assert.assertThat;
 import static org.junit.jupiter.api.Assertions.assertAll;
 import static org.mockito.Mockito.when;
 
 import java.sql.*;
 import java.util.List;
 import java.util.Optional;
+import java.util.logging.Logger;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -20,6 +20,7 @@
 import com.exasol.adapter.dialects.BaseIdentifierConverter;
 import com.exasol.adapter.metadata.DataType;
 import com.exasol.adapter.metadata.TableMetadata;
+import com.exasol.logging.CapturingLogHandler;
 
 @ExtendWith(MockitoExtension.class)
 class BaseTableMetadataReaderTest {
@@ -82,4 +83,13 @@ void testMapTablesIgnoresTablesThatHaveNoColumns() throws SQLException {
         assertAll(() -> assertThat(tables, iterableWithSize(1)), //
                 () -> assertThat(tableA.getName(), equalTo(TABLE_A)));
     }
+
+    @Test
+    void testWarnIfTableScanResultsAreEmpty() throws SQLException {
+        mockTableCount(this.tablesMock, 0);
+        final CapturingLogHandler capturingLogHandler = new CapturingLogHandler();
+        Logger.getLogger("com.exasol").addHandler(capturingLogHandler);
+        createDefaultTableMetadataReader().mapTables(this.tablesMock, Optional.empty());
+        assertThat(capturingLogHandler.getCapturedData(), containsString("Table scan did not find any tables."));
+    }
 }