Golang Gorm 使用 slices 和 postgres 的 jsob 字段

Question

I have a requirement to save either [] or a list with different integer values like [1, 7, 8]. These values can be anything between 1-31.

My struct for this field (DateOfMonth) is:

type Subscription struct {
    gorm.Model
    Enabled            bool    `gorm:"DEFAULT:True"`
    Deleted            bool    `gorm:"DEFAULT:False"`
    UserID             uint    `gorm:"not null"`
    Cap                int     `gorm:"DEFAULT:-1"`
    DateOfMonth        []int64 `gorm:"type:json default '[]'::json"`
}

Now, I need to read this value in an API and compare it with the current_date.

For this, I have tried:

type Result struct {
        ID               uint
        Email            string
        UniqueIdentifier string
        Cap              int
        DateOfMonth      []uint8
    }
    var subscriptions []Result
    if err := db.Table("users").Select("users.id, users.email, users.unique_identifier, subscriptions.cap, subscriptions.date_of_month").Joins("join subscriptions on users.id = subscriptions.user_id").Where("subscriptions.subscription_type_id=? and users.is_verified=? and subscriptions.enabled=?", subscription_type_id, true, true).Find(&subscriptions).Error; err != nil {
        c.JSON(http.StatusNotFound, gin.H{"error": true, "reason": "Subscribers not found!", "code": http.StatusBadRequest, "status": "failure"})
        return
    }

If I change DateOfMonth []uint8 to DateOfMonth []int64 , it gives error. The value that I receive in this field is a list of byte values For example, [] -> [91 93] and [6] -> [91 54 93]

If I do, bytes.NewBuffer(s.DateOfMonth) , I get the correct value but then I need to iterate over this slice to compare it with today's date. I have tried a lot of ways to get the actual value (6) in the loop (dom value) but to no avail.

// if len(s.DateOfMonth) > 0 {
        //  // date_of_month_new := binary.BigEndian.Uint64(date_of_month)
        //  todays_date_of_month := time.Now().Day()
        //  fmt.Println(todays_date_of_month) //, date_of_month, reflect.TypeOf(date_of_month))
        //  for _, dom := range s.DateOfMonth {
        //      fmt.Println("help", reflect.TypeOf(dom), dom, todays_date_of_month)
        //      // if dom == todays_date_of_month {
        //      //  fmt.Println("matching", dom, todays_date_of_month)
        //      // }
        //  }
        // }

I have even tried suggestions from various answers like this , this , this

What am I missing here? Your help will be highly appreciated.

Some of the errors that I got:

invalid sql type DateOfMonth (slice) for postgres
Golang cannot range over pointer to slice
cannot range over bytes.NewBuffer(s.DateOfMonth) (type *bytes.Buffer)
sql: Scan error on column index 4, name "date_of_month": unsupported Scan, storing driver.Value type []uint8 into type *[]int 

Answer 1

Golang cannot range over pointer to slice

You are iterating over a pointer to a slice, instead of a slice. This means you will have to first de-reference your variable and then loop over it. Check out this example .

 cannot range over bytes.NewBuffer(s.DateOfMonth) (type *bytes.Buffer)

You cannot range over type *bytes.Buffer . You can instead access the bytes of the type by using the method Buffer.Bytes() . Check out this example .

 sql: Scan error on column index 4, name "date_of_month": unsupported Scan, storing driver.Value type []uint8 into type *[]int

Judging by the error I'm guessing this happens when you use type []int64 while scanning DateOfMonth . One of the possibilities for this error is your database storing the values as []uint8 instead of []int64 .

invalid sql type DateOfMonth (slice) for postgres

I'll try and update my answer after I am able to reproduce this error successfully.