invalid sql type (map) for postgres

Question

I'm trying to save a nested struct into postgres using gorm, but I'm hitting some issues with my map[string]*InnerStruct type.

I want to store my map type as JSONB in postgres, so I've defined a Scanner/Valuer like so as suggested in similar questions:

type SomeMapType map[string]*InnerStruct

type StoreStruct struct {
    gorm.Model
    Id               string `gorm:"type:uuid;primary_key"`
    AccountID        string
    SomeMapType      SomeMapType `gorm:"column:cache,type:jsonb"`
}

var _ driver.Valuer = SomeMapType{}
var _ sql.Scanner = &SomeMapType{}

func (smt SomeMapType) Value() (driver.Value, error) {
    return json.Marshal(smt)
}

func (smt *SomeMapType) Scan(value interface{}) error {
    b, ok := value.([]byte)
    if !ok {
        return errors.New("type assertion to []byte failed")
    }

    return json.Unmarshal(b, &smt)
}

but when I try to create a table like so:

err := db.
        CreateTable(StoreStruct{}).
        Table(tableName).Error)

A panic occurs: panic: invalid sql type SomeMapType (map) for postgres [recovered]

It looks like this happens even before my Valuer/Scanner implementations are called.

Is it just not possible to store a map field on a struct you want to save to a DB with gorm?
I believe I've seen examples that seem to be working with map[string]interface{} so I'm not sure why my scenario is different?

Make sure to add a closing " to your struct tags for SomeMapType. — John
– John, Commented Aug 6, 2020 at 19:01
@User-Upvotedon'tsayThanks that link isn't that relevant because it's not dealing with a map[string]SomeType, I'm able to implement Scanner/Valuer for other types fine. — Arash Outadi
– Arash Outadi, Commented Aug 6, 2020 at 22:17

Arash Outadi · Accepted Answer · 2020-08-07 19:50:29Z

1

My problem was not including the SQL type tag annotation.

Making the changes below fixed my issue:

type StoreStruct struct {
    gorm.Model
    Id               string `gorm:"type:uuid;primary_key"`
    AccountID        string
    SomeMapType      SomeMapType `gorm:"column:cache" sql:"type:jsonb"`
}

edited Aug 7, 2020 at 19:50

answered Aug 7, 2020 at 17:27

Arash Outadi

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