Add schema to ArrowBatchIterator

internal/rows/arrowbased/arrowRecordIterator.go

@@ -1,10 +1,13 @@
 package arrowbased
 
 import (
+	"bytes"
 	"context"
+	"fmt"
 	"io"
 
 	"github.com/apache/arrow/go/v12/arrow"
+	"github.com/apache/arrow/go/v12/arrow/ipc"
 	"github.com/databricks/databricks-sql-go/internal/cli_service"
 	"github.com/databricks/databricks-sql-go/internal/config"
 	dbsqlerr "github.com/databricks/databricks-sql-go/internal/errors"
@@ -34,6 +37,7 @@ type arrowRecordIterator struct {
 	currentBatch       SparkArrowBatch
 	isFinished         bool
 	arrowSchemaBytes   []byte
+	arrowSchema        *arrow.Schema
 }
 
 var _ rows.ArrowBatchIterator = (*arrowRecordIterator)(nil)
@@ -170,3 +174,36 @@ func (ri *arrowRecordIterator) newBatchIterator(fr *cli_service.TFetchResultsRes
 		return NewLocalBatchIterator(ri.ctx, rowSet.ArrowBatches, rowSet.StartRowOffset, ri.arrowSchemaBytes, &ri.cfg)
 	}
 }
+
+// Return the schema of the records.
+func (ri *arrowRecordIterator) Schema() (*arrow.Schema, error) {
+	// Return cached schema if available
+	if ri.arrowSchema != nil {
+		return ri.arrowSchema, nil
+	}
+
+	// Try to get schema bytes if not already available
+	if ri.arrowSchemaBytes == nil {
+		if ri.HasNext() {
+			if err := ri.getCurrentBatch(); err != nil {
+				return nil, err
+			}
+		}
+
+		// If still no schema bytes, we can't create a schema
+		if ri.arrowSchemaBytes == nil {
+			return nil, fmt.Errorf("no schema available")
+		}
+	}
+
+	// Convert schema bytes to Arrow schema
+	reader, err := ipc.NewReader(bytes.NewReader(ri.arrowSchemaBytes))
+	if err != nil {
+		return nil, fmt.Errorf("failed to create Arrow IPC reader: %w", err)
+	}
+	defer reader.Release()
+
+	// Cache and return the schema
+	ri.arrowSchema = reader.Schema()
+	return ri.arrowSchema, nil
+}

internal/rows/arrowbased/arrowRecordIterator_test.go

@@ -188,6 +188,135 @@ func TestArrowRecordIterator(t *testing.T) {
 	})
 }
 
+func TestArrowRecordIteratorSchema(t *testing.T) {
+	// Test with arrowSchemaBytes available
+	t.Run("schema with initial schema bytes", func(t *testing.T) {
+		logger := dbsqllog.WithContext("connectionId", "correlationId", "")
+
+		executeStatementResp := cli_service.TExecuteStatementResp{}
+		loadTestData2(t, "directResultsMultipleFetch/ExecuteStatement.json", &executeStatementResp)
+
+		fetchResp1 := cli_service.TFetchResultsResp{}
+		loadTestData2(t, "directResultsMultipleFetch/FetchResults1.json", &fetchResp1)
+
+		var fetchesInfo []fetchResultsInfo
+		simpleClient := getSimpleClient(&fetchesInfo, []cli_service.TFetchResultsResp{fetchResp1})
+		rpi := rowscanner.NewResultPageIterator(
+			rowscanner.NewDelimiter(0, 0),
+			5000,
+			nil,
+			false,
+			simpleClient,
+			"connectionId",
+			"correlationId",
+			logger,
+		)
+
+		cfg := *config.WithDefaults()
+
+		bi, err := NewLocalBatchIterator(
+			context.Background(),
+			executeStatementResp.DirectResults.ResultSet.Results.ArrowBatches,
+			0,
+			executeStatementResp.DirectResults.ResultSetMetadata.ArrowSchema,
+			&cfg,
+		)
+		assert.Nil(t, err)
+
+		// Create arrowRecordIterator with schema bytes already available
+		rs := NewArrowRecordIterator(
+			context.Background(),
+			rpi,
+			bi,
+			executeStatementResp.DirectResults.ResultSetMetadata.ArrowSchema,
+			cfg,
+		)
+		defer rs.Close()
+
+		// Test Schema() method
+		schema, schemaErr := rs.Schema()
+		assert.NoError(t, schemaErr)
+		assert.NotNil(t, schema)
+
+		// Cache works - we should get same schema object on second call
+		secondSchema, schemaErr2 := rs.Schema()
+		assert.NoError(t, schemaErr2)
+		assert.Same(t, schema, secondSchema)
+	})
+
+	// Test with arrowSchemaBytes that needs to be populated via a batch
+	t.Run("schema with lazy loading", func(t *testing.T) {
+		logger := dbsqllog.WithContext("connectionId", "correlationId", "")
+
+		fetchResp1 := cli_service.TFetchResultsResp{}
+		loadTestData2(t, "multipleFetch/FetchResults1.json", &fetchResp1)
+
+		var fetchesInfo []fetchResultsInfo
+		simpleClient := getSimpleClient(&fetchesInfo, []cli_service.TFetchResultsResp{fetchResp1})
+		rpi := rowscanner.NewResultPageIterator(
+			rowscanner.NewDelimiter(0, 0),
+			5000,
+			nil,
+			false,
+			simpleClient,
+			"connectionId",
+			"correlationId",
+			logger,
+		)
+
+		cfg := *config.WithDefaults()
+
+		// Create arrowRecordIterator without initial schema bytes
+		rs := NewArrowRecordIterator(context.Background(), rpi, nil, nil, cfg)
+		defer rs.Close()
+
+		// Schema() should trigger loading a batch to get schema
+		schema, schemaErr := rs.Schema()
+		assert.NoError(t, schemaErr)
+		assert.NotNil(t, schema)
+
+		// Cache works - we should get same schema object on second call
+		secondSchema, schemaErr2 := rs.Schema()
+		assert.NoError(t, schemaErr2)
+		assert.Same(t, schema, secondSchema)
+	})
+
+	// Test with no schema available
+	t.Run("schema with no data available", func(t *testing.T) {
+		logger := dbsqllog.WithContext("connectionId", "correlationId", "")
+
+		// Instead of using an empty response list, let's create a custom client
+		// that returns an error when trying to fetch results
+		failingClient := &client.TestClient{
+			FnFetchResults: func(ctx context.Context, req *cli_service.TFetchResultsReq) (*cli_service.TFetchResultsResp, error) {
+				return nil, fmt.Errorf("no data available")
+			},
+		}
+
+		rpi := rowscanner.NewResultPageIterator(
+			rowscanner.NewDelimiter(0, 0),
+			5000,
+			nil,
+			false,
+			failingClient,
+			"connectionId",
+			"correlationId",
+			logger,
+		)
+
+		cfg := *config.WithDefaults()
+
+		// Create arrowRecordIterator without schema bytes and with failing client
+		rs := NewArrowRecordIterator(context.Background(), rpi, nil, nil, cfg)
+		defer rs.Close()
+
+		// Schema() should return error since no schema can be obtained
+		schema, schemaErr := rs.Schema()
+		assert.Error(t, schemaErr)
+		assert.Nil(t, schema)
+	})
+}
+
 type fetchResultsInfo struct {
 	direction      cli_service.TFetchOrientation
 	resultStartRec int

rows/rows.go

@@ -20,4 +20,7 @@ type ArrowBatchIterator interface {
 
 	// Release any resources in use by the iterator.
 	Close()
+
+	// Return the schema of the records.
+	Schema() (*arrow.Schema, error)
 }