debugmiller opened a new pull request, #9021:
URL: https://github.com/apache/arrow-rs/pull/9021
# Which issue does this PR close?
Closes #8987
# What changes are included in this PR?
This incorporates feedback from the discussion on #8998 and includes #7442
with some small adjustments.
With this change you can now register a custom decoder on arrow-json reader.
As a motivating example, this PR also provides the
`VariantArrayDecoderFactory` which allows for Variant annotated Fields to be
deserialized into Variant columns.
For example
```rust
let variant_array = VariantArrayBuilder::new(0).build();
let struct_field = Schema::new(vec![
Field::new("id", DataType::Int32, false),
// call VariantArray::field to get the correct Field
variant_array.field("var"),
]);
let builder = ReaderBuilder::new(Arc::new(struct_field.clone()));
let result = builder
.with_struct_mode(StructMode::ObjectOnly)
.with_decoder_factory(Arc::new(VariantArrayDecoderFactory))
.build(Cursor::new(b"{\"id\": 1, \"var\": [\"mixed data\", 1]}"));
```
This includes #7442 with only two minor changes:
- removed the default implementation of `make_default_decoder` in the
`DecoderFactory` trait, which seemed redundant
- adds `field` as a parameter to `make_decoder` which is necessary to
extract the extension information, although it is somewhat redundant.
@scovich I incorporated your review feedback from #8998, except where noted
inline in the code.
# Are these changes tested?
Unit test was added. Open to feedback on whether that test is adequate or
more is expected.
# Are there any user-facing changes?
Yes, users can now register custom decoders with arrow-json Reader, and use
`VariantArrayDecoderFactory` to deserialize json into Variant columns.
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