bigquery: support for nested JSON types

[leclark]

Is your feature request related to a problem? Please describe.

This PR added initial json support to the bigquery managedwriter/adapt pkg.

Unfortunately, it doesn't support using a json object as a field value. It errors if a regular nested json object is passed in.

The current test is using strings as the field values instead of json objects.

	sampleJSONData := [][]byte{
		[]byte(`{"json_type":"{\"foo\": \"bar\"}"}`),
		[]byte(`{"json_type":"{\"key\": \"value\"}"}`),
		[]byte(`{"json_type":"\"a string\""}`),
	}

Describe the solution you'd like

Add support for nested json objects that aren't strings and update the test to include a mix of types including nested json objects.

e.g.

	sampleJSONData := [][]byte{
		[]byte(`{"json_type":{"foo": "bar"}}`),
		[]byte(`{"json_type":{"key": "value"}}`),
		[]byte(`{"json_type":"a string"}`),
		[]byte(`{"json_type":{"outer": {"a": "value", "b": true, "c": 1, "d":[1, 2, 3]}}}`),
	}

Describe alternatives you've considered

Converting json objects to strings, but that requires custom data handling per message type.

Additional context

N/A

[alvarowolfx]

@leclark thanks for the report.

BigQuery JSON fields should be set with a valid JSON String, which is the same format that we need to send via the Storage Write API (some details on field conversions). For nested JSON objects to work in the example that was provided, the protobuf field type would have to be google.protobuf.Any or message, which would not be accepted by the Storage Write API, as it would be a mismatch from the table schema.

A workaround would be to have a custom type to insert data that converts the given field from a map[string]any to a escaped string like this:

package main

import (
	"encoding/json"
	"fmt"
)

type Example struct {
	JsonField JsonFieldType `json:"json_field"`
}

type JsonFieldType map[string]any

func (f JsonFieldType) MarshalJSON() ([]byte, error) {
	out, err := json.Marshal(map[string]any(f))
	if err != nil {
		return nil, err
	}
	// escape string
	return json.Marshal(string(out))
}

func main() {
	value := map[string]any{
		"outer": map[string]any{
			"a": "value",
			"b": true,
			"c": 1,
			"d": []int{1, 2, 3, 4},
		},
	}
	ex := &Example{JsonField: value}
	out, _ := json.Marshal(ex)
	fmt.Println(string(out))
}
// OUTPUT: {"json_field":"{\"outer\":{\"a\":\"value\",\"b\":true,\"c\":1,\"d\":[1,2,3,4]}}"}