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58 lines
2.2 KiB
Markdown
58 lines
2.2 KiB
Markdown
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# Package `jsonw`
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Package `jsonw` implements JSON output writers.
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Note that there are three implementations of `output.RecordWriter`.
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- `NewStdRecordWriter` returns a writer that outputs in "standard" JSON.
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- `NewArrayRecordWriter` outputs each record on its own line as an element of a JSON array.
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- `NewObjectRecordWriter` outputs each record as a JSON object on its own line.
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These `RecordWriter`s correspond to the `--json`, `--jsona`, and `--jsonl` flags (where `jsonl` means "JSON Lines"). There are also other writer implementations, such as an `output.ErrorWriter` and an `output.MetadataWriter`.
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#### Standard JSON `--json`:
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```json
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[
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{
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"actor_id": 1,
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"first_name": "PENELOPE",
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"last_name": "GUINESS",
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"last_update": "2020-06-11T02:50:54Z"
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},
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{
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"actor_id": 2,
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"first_name": "NICK",
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"last_name": "WAHLBERG",
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"last_update": "2020-06-11T02:50:54Z"
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}
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]
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```
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#### JSON Array `--jsona`:
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```json
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[1, "PENELOPE", "GUINESS", "2020-06-11T02:50:54Z"]
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[2, "NICK", "WAHLBERG", "2020-06-11T02:50:54Z"]
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```
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#### Object aka JSON Lines `--jsonl`:
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```json
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{"actor_id": 1, "first_name": "PENELOPE", "last_name": "GUINESS", "last_update": "2020-06-11T02:50:54Z"}
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{"actor_id": 2, "first_name": "NICK", "last_name": "WAHLBERG", "last_update": "2020-06-11T02:50:54Z"}
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```
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## Notes
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At the time of development there was not a JSON encoder library available that provided the functionality that `sq` required. These requirements:
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- Optional colorization
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- Optional pretty-printing (indentation, spacing)
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- Preservation of the order of record fields (columns).
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For the `RecordWriter` implementations, given the known "flat" structure of a record, it was relatively straightforward to create custom writers for each type of JSON output.
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For general-purpose JSON output (such as metadata output), it was necessary to modify an existing JSON library to provide colorization (and also on-the-fly indentation). After benchmarking, the [segmentio.io encoder](https://github.com/segmentio/encoding) was selected as the base library. Rather than a separate forked project (which probably would not make sense to ever merge with its parent project), the modified encoder is found in `jsonw/internal/jcolorenc`.
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