fix: Add query dryRun logic to get the schema when null schema is returned from the backend

google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/ConnectionImpl.java

@@ -192,7 +192,7 @@ public BigQueryResult executeSelect(String sql) throws BigQuerySQLException {
       if (isFastQuerySupported()) {
         String projectId = bigQueryOptions.getProjectId();
         QueryRequest queryRequest = createQueryRequest(connectionSettings, sql, null, null);
-        return queryRpc(projectId, queryRequest, false);
+        return queryRpc(projectId, queryRequest, sql, false);
       }
       // use jobs.insert otherwise
       com.google.api.services.bigquery.model.Job queryJob =
@@ -236,7 +236,7 @@ public BigQueryResult executeSelect(
         final String projectId = bigQueryOptions.getProjectId();
         final QueryRequest queryRequest =
             createQueryRequest(connectionSettings, sql, parameters, labelMap);
-        return queryRpc(projectId, queryRequest, parameters != null);
+        return queryRpc(projectId, queryRequest, sql, parameters != null);
       }
       // use jobs.insert otherwise
       com.google.api.services.bigquery.model.Job queryJob =
@@ -289,7 +289,10 @@ public int size() {
   }
 
   private BigQueryResult queryRpc(
-      final String projectId, final QueryRequest queryRequest, Boolean hasQueryParameters) {
+      final String projectId,
+      final QueryRequest queryRequest,
+      String sql,
+      Boolean hasQueryParameters) {
     com.google.api.services.bigquery.model.QueryResponse results;
     try {
       results =
@@ -322,8 +325,29 @@ private BigQueryResult queryRpc(
       // and can be optimized here, but this is left as future work.
       Long totalRows = results.getTotalRows() == null ? null : results.getTotalRows().longValue();
       Long pageRows = results.getRows() == null ? null : (long) (results.getRows().size());
+      logger.log(
+          Level.WARNING,
+          "\n"
+              + String.format(
+                  "results.getJobComplete(): %s, isSchemaNull: %s , totalRows: %s, pageRows: %s",
+                  results.getJobComplete(), results.getSchema() == null, totalRows, pageRows));
       JobId jobId = JobId.fromPb(results.getJobReference());
       GetQueryResultsResponse firstPage = getQueryResultsFirstPage(jobId);
+      // We might get null schema from the backend occasionally. Ref:
+      // https://github.com/googleapis/java-bigquery/issues/2103/. Using queryDryRun in such cases
+      // to get the schema
+      if (firstPage.getSchema() == null) { // get schema using dry run
+        // Log the status if the job was complete complete
+        logger.log(
+            Level.WARNING,
+            "\n"
+                + "Received null schema, Using dryRun the get the Schema. jobComplete:"
+                + firstPage.getJobComplete());
+        com.google.api.services.bigquery.model.Job dryRunJob = createDryRunJob(sql);
+        Schema schema = Schema.fromPb(dryRunJob.getStatistics().getQuery().getSchema());
+        return getSubsequentQueryResultsWithJob(
+            totalRows, pageRows, jobId, firstPage, schema, hasQueryParameters);
+      }
       return getSubsequentQueryResultsWithJob(
           totalRows, pageRows, jobId, firstPage, hasQueryParameters);
     }
@@ -1243,7 +1267,8 @@ com.google.api.services.bigquery.model.Job createQueryJob(
   }
 
   // Used by dryRun
-  private com.google.api.services.bigquery.model.Job createDryRunJob(String sql) {
+  @VisibleForTesting
+  com.google.api.services.bigquery.model.Job createDryRunJob(String sql) {
     com.google.api.services.bigquery.model.JobConfiguration configurationPb =
         new com.google.api.services.bigquery.model.JobConfiguration();
     configurationPb.setDryRun(true);

google-cloud-bigquery/src/test/java/com/google/cloud/bigquery/ConnectionImplTest.java

@@ -93,6 +93,26 @@ public class ConnectionImplTest {
           .setTotalRows(BigInteger.valueOf(1L))
           .setSchema(FAST_QUERY_TABLESCHEMA);
 
+  private static final GetQueryResultsResponse GET_QUERY_RESULTS_RESPONSE_NULL_SCHEMA =
+      new GetQueryResultsResponse()
+          .setJobReference(QUERY_JOB.toPb())
+          .setRows(ImmutableList.of(TABLE_ROW))
+          .setJobComplete(false)
+          .setPageToken(PAGE_TOKEN)
+          .setTotalBytesProcessed(42L)
+          .setTotalRows(BigInteger.valueOf(1L))
+          .setSchema(null);
+
+  private static List<TableRow> TABLE_ROWS =
+      ImmutableList.of(
+          new TableRow()
+              .setF(
+                  ImmutableList.of(new TableCell().setV("Value1"), new TableCell().setV("Value2"))),
+          new TableRow()
+              .setF(
+                  ImmutableList.of(
+                      new TableCell().setV("Value3"), new TableCell().setV("Value4"))));
+
   private BigQueryOptions createBigQueryOptionsForProject(
       String project, BigQueryRpcFactory rpcFactory) {
     return BigQueryOptions.newBuilder()
@@ -211,24 +231,13 @@ public void testQueryDryRun() throws BigQuerySQLException {
 
   @Test
   public void testParseDataTask() throws InterruptedException {
-    List<TableRow> tableRows =
-        ImmutableList.of(
-            new TableRow()
-                .setF(
-                    ImmutableList.of(
-                        new TableCell().setV("Value1"), new TableCell().setV("Value2"))),
-            new TableRow()
-                .setF(
-                    ImmutableList.of(
-                        new TableCell().setV("Value3"), new TableCell().setV("Value4"))));
-
     BlockingQueue<Tuple<Iterable<FieldValueList>, Boolean>> pageCache =
         new LinkedBlockingDeque<>(2);
     BlockingQueue<Tuple<TableDataList, Boolean>> rpcResponseQueue = new LinkedBlockingDeque<>(2);
     rpcResponseQueue.offer(Tuple.of(null, false));
     // This call should populate page cache
     ConnectionImpl connectionSpy = Mockito.spy(connection);
-    connectionSpy.parseRpcDataAsync(tableRows, QUERY_SCHEMA, pageCache, rpcResponseQueue);
+    connectionSpy.parseRpcDataAsync(TABLE_ROWS, QUERY_SCHEMA, pageCache, rpcResponseQueue);
     Tuple<Iterable<FieldValueList>, Boolean> fvlTupple =
         pageCache.take(); // wait for the parser thread to parse the data
     assertNotNull(fvlTupple);
@@ -247,16 +256,6 @@ public void testParseDataTask() throws InterruptedException {
 
   @Test
   public void testPopulateBuffer() throws InterruptedException {
-    List<TableRow> tableRows =
-        ImmutableList.of(
-            new TableRow()
-                .setF(
-                    ImmutableList.of(
-                        new TableCell().setV("Value1"), new TableCell().setV("Value2"))),
-            new TableRow()
-                .setF(
-                    ImmutableList.of(
-                        new TableCell().setV("Value3"), new TableCell().setV("Value4"))));
 
     BlockingQueue<Tuple<Iterable<FieldValueList>, Boolean>> pageCache =
         new LinkedBlockingDeque<>(2);
@@ -266,7 +265,7 @@ public void testPopulateBuffer() throws InterruptedException {
     // This call should populate page cache
     ConnectionImpl connectionSpy = Mockito.spy(connection);
 
-    connectionSpy.parseRpcDataAsync(tableRows, QUERY_SCHEMA, pageCache, rpcResponseQueue);
+    connectionSpy.parseRpcDataAsync(TABLE_ROWS, QUERY_SCHEMA, pageCache, rpcResponseQueue);
 
     verify(connectionSpy, times(1))
         .parseRpcDataAsync(
@@ -358,19 +357,62 @@ public void testLegacyQuerySinglePage() throws BigQuerySQLException {
         .createJobForQuery(any(com.google.api.services.bigquery.model.Job.class));
   }
 
+  // calls executeSelect with a Fast query and emulates that no schema is returned with the first
+  // page
+  @Test
+  public void testFastQueryNullSchema() throws BigQuerySQLException {
+    ConnectionImpl connectionSpy = Mockito.spy(connection);
+    QueryRequest queryReqMock = new QueryRequest();
+    com.google.api.services.bigquery.model.JobStatistics stats =
+        new com.google.api.services.bigquery.model.JobStatistics()
+            .setQuery(new JobStatistics2().setSchema(FAST_QUERY_TABLESCHEMA));
+    com.google.api.services.bigquery.model.Job jobResponseMock =
+        new com.google.api.services.bigquery.model.Job()
+            // .setConfiguration(QUERY_JOB.g)
+            .setJobReference(QUERY_JOB.toPb())
+            .setId(JOB)
+            .setStatus(new com.google.api.services.bigquery.model.JobStatus().setState("DONE"))
+            .setStatistics(stats);
+    // emulating a legacy query
+    doReturn(true).when(connectionSpy).isFastQuerySupported();
+    com.google.api.services.bigquery.model.QueryResponse mockQueryRes =
+        new QueryResponse()
+            .setSchema(FAST_QUERY_TABLESCHEMA)
+            .setJobComplete(false) // so that it goes to the else part in queryRpc
+            .setTotalRows(new BigInteger(String.valueOf(4L)))
+            .setJobReference(QUERY_JOB.toPb())
+            .setRows(TABLE_ROWS);
+    when(bigqueryRpcMock.queryRpc(any(String.class), any(QueryRequest.class)))
+        .thenReturn(mockQueryRes);
+    doReturn(GET_QUERY_RESULTS_RESPONSE_NULL_SCHEMA) // wiring the null schema for the test case
+        .when(connectionSpy)
+        .getQueryResultsFirstPage(any(JobId.class));
+    doReturn(BQ_RS_MOCK_RES)
+        .when(connectionSpy)
+        .getSubsequentQueryResultsWithJob(
+            any(Long.class),
+            any(Long.class),
+            any(JobId.class),
+            any(GetQueryResultsResponse.class),
+            any(Schema.class),
+            any(Boolean.class));
+    doReturn(jobResponseMock).when(connectionSpy).createDryRunJob(any(String.class));
+    BigQueryResult res = connectionSpy.executeSelect(SQL_QUERY);
+    assertEquals(res.getTotalRows(), 2);
+    assertEquals(QUERY_SCHEMA, res.getSchema());
+    verify(connectionSpy, times(1))
+        .getSubsequentQueryResultsWithJob(
+            any(Long.class),
+            any(Long.class),
+            any(JobId.class),
+            any(GetQueryResultsResponse.class),
+            any(Schema.class),
+            any(Boolean.class));
+  }
+
   // exercises getSubsequentQueryResultsWithJob for fast running queries
   @Test
   public void testFastQueryLongRunning() throws SQLException {
-    List<TableRow> tableRows =
-        ImmutableList.of(
-            new TableRow()
-                .setF(
-                    ImmutableList.of(
-                        new TableCell().setV("Value1"), new TableCell().setV("Value2"))),
-            new TableRow()
-                .setF(
-                    ImmutableList.of(
-                        new TableCell().setV("Value3"), new TableCell().setV("Value4"))));
     ConnectionImpl connectionSpy = Mockito.spy(connection);
     // emulating a fast query
     doReturn(true).when(connectionSpy).isFastQuerySupported();
@@ -389,7 +431,7 @@ public void testFastQueryLongRunning() throws SQLException {
             .setJobComplete(false)
             .setTotalRows(new BigInteger(String.valueOf(4L)))
             .setJobReference(QUERY_JOB.toPb())
-            .setRows(tableRows);
+            .setRows(TABLE_ROWS);
     when(bigqueryRpcMock.queryRpc(any(String.class), any(QueryRequest.class)))
         .thenReturn(mockQueryRes);
     BigQueryResult res = connectionSpy.executeSelect(SQL_QUERY);