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Propagate error in TFetchResults #255

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jackyhu-db merged 1 commit into from
Mar 18, 2025
Merged

Propagate error in TFetchResults #255

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5 changes: 0 additions & 5 deletions internal/rows/rows.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@ import (
"context"
"database/sql"
"database/sql/driver"
"io"
"math"
"reflect"
"time"
Expand Down Expand Up @@ -456,10 +455,6 @@ func (r *rows) fetchResultPage() error {
r.RowScanner = nil
}

if !r.ResultPageIterator.HasNext() {
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@jackyhu-db jackyhu-db Mar 13, 2025

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can you check the r.error and return r.error instead?

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@mdibaiee mdibaiee Mar 14, 2025

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@jackyhu-db I think it is possible to do a check like that, but I would like to clarify what is the use of HasNext if Next itself can just return nil, io.EOF to signify an end of the stream?

My question is more structural: why the additional complexity of HasNext when Next itself can interface and encapsulate the concept of HasNext? It is possible to now check for the error in r.ResultPageIterator.err and bubble that up, but I'm afraid any divergence between Next's logic and HasNext's logic in the future can lead to similar problems

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@mdibaiee mdibaiee Mar 14, 2025 •
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I think it is worth considering whether HasNext can be simply rewritten as: r.ResultPageIterator.Next() == (nil, io.EOF), and if so, it is not really useful to keep it, any consumer of ResultPageIterator can use Next for the purpose of checking whether there are any items left or not

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@vikrantpuppala vikrantpuppala Mar 15, 2025

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@jackyhu-db, we would also need to update the function signature to return (bool, error) and also make changes to https://github.com/databricks/databricks-sql-go/blob/main/internal/rows/arrowbased/arrowRecordIterator.go#L86 to also return the error, do we want to go down that route?

return io.EOF
}

fetchResult, err1 := r.ResultPageIterator.Next()
if err1 != nil {
return err1
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27 changes: 27 additions & 0 deletions internal/rows/rows_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1506,3 +1506,30 @@ func getSimpleClient(fetchResults []cli_service.TFetchResultsResp) cli_service.T

return client
}

func getErroringClient(err error) cli_service.TCLIService {
fetchResultsFn := func(ctx context.Context, req *cli_service.TFetchResultsReq) (_r *cli_service.TFetchResultsResp, _err error) {
return nil, err
}

client := &client.TestClient{
FnFetchResults: fetchResultsFn,
}

return client
}

func TestFetchResultPage_PropagatesGetNextPageError(t *testing.T) {
errorMsg := "Error thrown while calling TFetchResults in getNextPage"
expectedErr := errors.New(errorMsg)

client := getErroringClient(expectedErr)

executeStatementResp := cli_service.TExecuteStatementResp{}
cfg := config.WithDefaults()
rows, _ := NewRows("connId", "corrId", nil, client, cfg, executeStatementResp.DirectResults)
// Call Next and ensure it propagates the error from getNextPage
actualErr := rows.Next(nil)

assert.ErrorContains(t, actualErr, errorMsg)
}
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