How can I insert a golang map into PostgreSQL

Question

I have a json object sent from a mobile application, looks like this:

{
    "product_id": "0123456789",
    "name": "PRODUCT_NAME",
    "manufacturer": "PRODUCT_MANUFACTURER",
    "image_url": "IMAGE_URL",
    "additional_info": "",
    "store_id": "STORE_ID",
    "store_name": "STORE_NAME",
    "owner_id": "OWNER_ID",
    "quantities": {
        "1000": 10.0,
        "1500": 12.0,
    }
}

The key value in quantities is a for example, can be grams, and the value is a representes a price. So for example, 1000 grams of rice will cost 10$, and 1500 grams of rice will cost 12.0$ (as a sale or something)

I have a Model Object in my Go code, that has the quantities filed as map[int]float32 I'm trying to find a way to insert this map into a PostgreSQL database I have, but can't figure out how.

This is my Go Model:

type Product struct {
    ID             string          
    UUID           string          
    Name           string         
    Manufacturer   string         
    ImageURL       string         
    AdditionalInfo string          
    StoreID        string         
    StoreName      string          
    OwnerID        string          
    Quantities     map[int]float32
}

I read about JSONB but won't it return a json when I retrieve the data? I need it to return a map[int]float32 and not json.

Eklavya · Accepted Answer · 2020-06-12 18:11:24Z

2

You need to implement driver.Valuer and sql.Scanner interface for save as JSONB

The driver.Valuer interface, such that it marshals the object into a JSON byte slice that can be understood by the database.

The sql.Scanner interface, such that it unmarshals a JSON byte slice from the database into the struct fields.

And for json Marshal you need to convert map[int]float32 into map[string]float32

type cusjsonb map[int]float32

// Returns the JSON-encoded representation
func (a cusjsonb) Value() (driver.Value, error) {
    // Convert to map[string]float32 from map[int]float32 
    x := make(map[string]float32)
    for k, v := range a {
       x[strconv.FormatInt(int64(k), 10)] = v
    }
    // Marshal into json 
    return json.Marshal(x)
}

// Decodes a JSON-encoded value
func (a *cusjsonb) Scan(value interface{}) error {
    b, ok := value.([]byte)
    if !ok {
        return errors.New("type assertion to []byte failed")
    }
    // Unmarshal from json to map[string]float32
    x := make(map[string]float32)
    if err := json.Unmarshal(b, &x); err != nil {
       return err
    }
    // Convert to map[int]float32 from  map[string]float32
    *a = make(cusjsonb, len(x))
    for k, v := range x {
      if ki, err := strconv.ParseInt(k, 10, 32); err != nil {
         return err
      } else {
         (*a)[int(ki)] = v
      }
    }
    return nil
}

edited Jun 12, 2020 at 18:11

answered Jun 12, 2020 at 18:02

Eklavya

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1 Comment

John Doah Over a year ago

Thank you very much!

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