Storing Golang JSON into Postgresql

Question

I want to store a certain struct into my database that has a JSON field within it.

type Comp struct {
    CompId               int64           `db:"comp_id" json:"comp_id"`
    StartDate            time.Time       `db:"start_date" json:"start_date"`
    EndDate              time.Time       `db:"end_date" json:"end_date"`
    WeeklySchedule       json.RawMessage `db:"weekly_schedule" json:"weekly_schedule"`
}

The schema for the table is:

CREATE TABLE IF NOT EXISTS Tr.Comp(
    comp_id                 SERIAL,
    start_date              timestamp NOT NULL,
    end_date                timestamp NOT NULL,
    weekly_schedule         json NOT NULL,
    PRIMARY KEY (comp_id)
);

I am using sqlx and lib/pq driver in my project and the following will not execute. Instead it panics saying there is a nil pointer. DB is a global *sqlx.DB struct

    tx := DB.MustBegin()

    compFixture := Comp{
        StartDate:            time.Now(),
        EndDate:              time.Now().AddDate(1, 0, 0),
        WeeklySchedule:       json.RawMessage([]byte("{}")),
    }
    _, err = tx.NamedExec(
        `INSERT INTO 
            Tr.Comp(comp_id, 
                start_date, end_date, weekly_schedule) 
            VALUES (DEFAULT, 
                :start_date, :end_date, :weekly_schedule)  
            RETURNING comp_id;`, compFixture)
    if err != nil {
        t.Fatal("Error creating fixture.", err)
    }

When I remove weekly_schedule from the schema and fixture things run fine. But for some reason, the when this field is included, the program panics. Any idea as to how I should define the weekly_schedule field in both my DB schema and Go struct?

Answer 1

sqlx has a type JSONText in github.com/jmoiron/sqlx/types that will do what you need

doc for JSONText

Answer 2

I don't know how clean of a solution this is but I ended up making my own data type JSONRaw . The DB driver sees it as a []btye but it can still be treated like a json.RawMessage in the Go Code.

type JSONRaw json.RawMessage

func (j JSONRaw) Value() (driver.Value, error) {
    byteArr := []byte(j)

    return driver.Value(byteArr), nil
}

func (j *JSONRaw) Scan(src interface{}) error {
    asBytes, ok := src.([]byte)
    if !ok {
        return error(errors.New("Scan source was not []bytes"))
    }
    err := json.Unmarshal(asBytes, &j)
    if err != nil {
        return error(errors.New("Scan could not unmarshal to []string"))
    }

    return nil
}

func (m *JSONRaw) MarshalJSON() ([]byte, error) {
    return *m, nil
}

func (m *JSONRaw) UnmarshalJSON(data []byte) error {
    if m == nil {
        return errors.New("json.RawMessage: UnmarshalJSON on nil pointer")
    }
    *m = append((*m)[0:0], data...)
    return nil
}

This is copy paste reimplementation of MarshalJSON and UnmarshalJSON from the encoding/json library.

Answer 3

from the go documentation:

json.RawMessage is a raw encoded JSON object. It implements Marshaler and Unmarshaler and can be used to delay JSON decoding or precompute a JSON encoding.

if you log.Printf("%#", colors) in the example provided at package json json.RawMessage you can see that after unmarshalling the json object 'Point'-member isn't unmarshalled but left in []byte format until the color-format is fixed and 'Point' is unmarshalled explicitly.

Did you try something like unmarshal WeeklySchedule before putting it into the DB?