Not able to create query with dataSource as type query

[saketbairoliya2]

I'm trying to run following query:

{
	"queryType": "timeseries",
	"dataSource": {
		"type": "query",
		"query": {
			"aggregations": [
				{
					"fieldName": "count",
					"name": "count",
					"type": "longSum"
				}
			],
			"dataSource": {
				"name": "dc_94b4f5fdfde940979b79c50539d8322a_b42fde98efed4e638a0016b34b3c10cf_dataset_pre",
				"type": "table"
			},
			"dimension": {
				"dimension": "string_value",
				"type": "default"
			},
			"filter": {
				"fields": [
					{
						"dimension": "_split_name__",
						"type": "selector",
						"value": "train"
					},
					{
						"dimension": "column_name",
						"type": "selector",
						"value": "addressState"
					}
				],
				"type": "and"
			},
			"granularity": "day",
			"intervals": {
				"intervals": [
					"${__from:date:iso}/${__to:date:iso}"
				],
				"type": "intervals"
			},
			"metric": {
				"metric": "count",
				"type": "numeric"
			},
			"queryType": "topN",
			"threshold": 100
		}
	},
	"intervals": {
		"type": "intervals",
		"intervals": [
			"${__from:date:iso}/${__to:date:iso}"
		]
	},
	"granularity": "day"
}

Getting error for query to be null - Looks like we're always returning null here: https://github.com/grafadruid/go-druid/blob/master/builder/datasource/query.go#L24

[bourbonkk]

@saketbairoliya2
I fixed this bug in #82 PR

There were code modifications.
Query struct : "-,omitempty" -> "query,omitempty"

type Query struct {
	Base
	Query builder.Query `json:"query,omitempty"`
}

This is necessary to make a subquery.

And I wrote the test code for the subquery, so please check it out.