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Add AppendRows helper #1884

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merged 1 commit into from
Jan 23, 2024
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Add AppendRows helper #1884

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11 changes: 7 additions & 4 deletions rows.go
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Original file line number Diff line number Diff line change
Expand Up @@ -417,12 +417,10 @@ type CollectableRow interface {
// RowToFunc is a function that scans or otherwise converts row to a T.
type RowToFunc[T any] func(row CollectableRow) (T, error)

// CollectRows iterates through rows, calling fn for each row, and collecting the results into a slice of T.
func CollectRows[T any](rows Rows, fn RowToFunc[T]) ([]T, error) {
// AppendRows iterates through rows, calling fn for each row, and appending the results into a slice of T.
func AppendRows[T any, S ~[]T](slice S, rows Rows, fn RowToFunc[T]) (S, error) {
defer rows.Close()

slice := []T{}

for rows.Next() {
value, err := fn(rows)
if err != nil {
Expand All @@ -438,6 +436,11 @@ func CollectRows[T any](rows Rows, fn RowToFunc[T]) ([]T, error) {
return slice, nil
}

// CollectRows iterates through rows, calling fn for each row, and collecting the results into a slice of T.
func CollectRows[T any](rows Rows, fn RowToFunc[T]) ([]T, error) {
return AppendRows([]T(nil), rows, fn)
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After updating from 5.5.1 to 5.5.3, our integration tests failed.

Diff:
--- Expected
+++ Actual
@@ -12,4 +12,3 @@
unknownFields: ([]uint8) <nil>,
- Edges: ([]*edgev1.Edge) {
- }
+ Edges: ([]*edgev1.Edge) <nil>
})

When SELECT * FROM table WHERE ... returns no rows, 5.5.1 returns empty slice:

pgx/rows.go

Line 424 in ba05097

slice := []T{}

5.5.3 returns nil slice:

pgx/rows.go

Line 441 in 6f8f6ed

return AppendRows([]T(nil), rows, fn)

@jackc I believe this is an unintentional change introduced in this PR.

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I don't think that CollectRows was ever documented to return the dangling slice instead of the nil slice when no items were collected, but it's a simple enough fix (just change the call to AppendRows to be AppendRows([]T{}, rows, fn)).

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I don't think empty vs. nil slice was promised, but may as well preserve the previous behavior.

}

// CollectOneRow calls fn for the first row in rows and returns the result. If no rows are found returns an error where errors.Is(ErrNoRows) is true.
// CollectOneRow is to CollectRows as QueryRow is to Query.
func CollectOneRow[T any](rows Rows, fn RowToFunc[T]) (T, error) {
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