How to convert postgresql json type to golang native?

Question

I am trying to convert a postgres column that is of type json to golang json object.

type MY_JSON struct {
  MY_ID string `json:"my_id"`
  MY_INFO []MY_INNER_JSON `json:"my_info"`
}

type MY_INNER_JSON struct {
    SOME_ID   string `json:"some_id"`
    SOME_NUM  int64 `json:"some_num"`
    SOME_OPTIONAL  string `json:"some_optional,omitempty"`
}

rows, err := db.Query("SELECT my_json FROM my_json_table LIMIT 1;")

for rows.Next() {
    var mycolumn MY_JSON
    err = rows.Scan(&mycolumn)
    fmt.Println(mycolumn)
}

This is what the json looks like

{
    "my_id": "this is my_id",
    "my_info": [
        {
            "some_id": "some_id",
            "some_num": 123
        },
        {
            "some_id": "some_id",
            "some_num": 123,
            "some_optional": "sometimes more"
        },
    ]
}

I am getting panic from golang during runtime.

Can someone point me a direction and tell me where I am doing wrong?

Have the MY_JSON type implement the sql.Scanner interface using json.Unmarshal. (make sure to implement the Scanner on a pointer type) — mkopriva
– mkopriva, Commented Jan 12, 2019 at 16:45
You would do well to rename your variables to be more Go idiomatic. Take a look at the naming suggestions in Effective Go. — Jonathan Hall
– Jonathan Hall, Commented Jan 12, 2019 at 16:50

ford · Accepted Answer · 2019-01-12 17:02:53Z

3

By implementing the sql.Scanner interface on MY_JSON, your code should work as is. To do this, you need only to add the Scan method on the MY_JSON type (with pointer receiver).

func (m *MY_JSON) Scan(src interface{}) error {
    bs, ok := src.([]byte)
    if !ok {
        return errors.New("not a []byte")
    }
    return json.Unmarshal(bs, m)
}

answered Jan 12, 2019 at 17:02

ford

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