doupao1530
2014-09-10 05:48 浏览 128

将Golang JSON存储到Postgresql中

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?

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3条回答 默认 最新

  • 已采纳
    doulv8162 doulv8162 2014-09-11 21:43

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

    doc for JSONText

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  • douda5227 douda5227 2014-09-10 06:29

    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.

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  • dosc9472 dosc9472 2014-09-10 08:39

    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?

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