Golang上的JSON-解组石墨数据

Question

I am playing around with Golang and JSON trying to do some calculations with data extracted from Graphite API.

For simplicity, a snippet of the data sent by Graphite is:

[
{
    "target": "server1.loadavg.1min",
    "datapoints": [
        [
            0.16,
            1422770850
        ],
        [
            0.16,
            1422770880
        ],
        [
            null,
            1422771120
        ]
    ]
},
{
    "target": "server2.loadavg.1min",
    "datapoints": [
        [
            0.19,
            1422770850
        ],
        [
            null,
            1422771390
        ],
        [
            0.14,
            1422771420
        ]
    ]
}
]

I've been reading through the go json tutorial about how to use a generic interface{} for JSON arbitrary data, but I'm struggling with some aspects of the process.

I've tried to define a structure that will hold this data, read the file contents and unmarshal it to this structure:

type Graphite struct {
  Metric struct {
    Target     string      `json:"target"`
    Datapoints [][]float64 `json:"datapoints"`
  }
}

var results []Graphite
err = json.Unmarshal(d, &r)
if err != nil {
    panic(err)
}
fmt.Printf("%v
", r)

But the result is:

[{{ []}} {{ []}}]

I could do it of course with a generic interface{} but I would like to know what am I missing here.

Could you please help me?

Thank you!

Answer 1

I like to start at the simplest type and work my way out. First you need to represent your data point.

type DataPoint []float64

Then a metric is just a target and a series of data points.

type Metric struct {
    Target string      `json:"target"`
    Points []DataPoint `json:"datapoints"`
}

There is no need for your Graphite struct. Your JSON is just a JSON array of Metrics.

var results []Metric
err := json.Unmarshal([]byte(data), &results)

Here's a playground link with a complete example.