serramatutu commented on code in PR #833:
URL: https://github.com/apache/arrow-go/pull/833#discussion_r3864335360
##########
arrow/array/util.go:
##########
@@ -296,7 +296,11 @@ func RecordToJSON(rec arrow.RecordBatch, w io.Writer)
error {
cols := make(map[string]interface{})
for i := 0; int64(i) < rec.NumRows(); i++ {
for j, c := range rec.Columns() {
- cols[fields[j].Name] = c.GetOneForMarshal(i)
+ if rec.Schema().Field(j).Nullable && c.IsNull(i) {
Review Comment:
Per this: https://github.com/serramatutu/arrow-internal-nulls
In C++, it looks like the general approach is "validate all data in", then
assume it's OK/consistent when "writing out". I.e it is an invariant that the
data is correct when writing out.
If the user has messed around with the data:
- by tweaking memory directly: they need to ensure their code respects
invariants OR call ValidateFull
- by using a public API: the API will always leave the array in a consistent
internal state
This is my rationale for calling GetOneForMarshal() here: we assume the data
is correct, if it's not then it's UB.
If we're very pedantic about this, we should just revert this change and use
`c.GetOneForMarshal(i)` as we should assume `IsNull(i)` will always return
false. This is what C++ does actually, so here we're doing even more validation
by checking `rec.Schema().Field(j).Nullable`.
Sources:
- `JsonWriter::WriteArray` uses an `ArrayWriter`:
https://github.com/apache/arrow/blob/b12755a1cc41ee5e9b1874ece3bcc92d6d3e3e78/cpp/src/arrow/integration/json_internal.cc#L2079
- `ArrayWriter::WriteDataValues` does not check for the schema:
https://github.com/apache/arrow/blob/b12755a1cc41ee5e9b1874ece3bcc92d6d3e3e78/cpp/src/arrow/integration/json_internal.cc#L505
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