Preventing null (or empty string values in the db)

Question

I'm using PostgreSQL and GORM in my Go app.

I thought that using the sql tab of sql:"not null" would do the trick of preventing a null entry, but when go initializes structs with a string type then it defaults to an empty string which is not the same as null in the db.

I am wondering if there is a way to prevent this from happening in a struct definition so I wouldn't have to strictly enforce it at all levels in the application code.

Mcmullan

An empty string is the "not null" version of a string, no? – Colombia

its not enforcing it for me..If I got to my db manually and try to enter a null field then it says it violates not null constraint, but if I enter '' then it accepts it – Mcmullan

@deltaskelta: That's exactly what it should do. What's your question? – Rejoin

the last line of my question is what I am asking. Is there a way to prevent an empty string from being valid without strictly enforcing it through application code? – Mcmullan

No, there's no way within a struct definition to specify that some specific value is invalid. – Rejoin

why don't you declare your field as sql.NullString? – Upgrade

Use defaults instead gorm:"default:'empty'". Or prevent calls to db.Create at application level. – Atheroma

Answer 1

You can solve this problem of preventing '' (empty) string insertion into the database by using default: null and not null constraint together. SO if Struct field values are empty it will be consider as default value null and gorm will throw an error.

gorm:"unique;not null;type:varchar(100);default:null"

Example is:

type User struct {
    gorm.Model
    Email  string    `gorm:"unique;not null;type:varchar(100);default:null"`

}

SO gorm for empty User.Email will throw an error.

Straw

This works nicely. Nice way to solve this! Setting it this way, trying to pass in empty Email would create an error similar to: ERROR: null value in column "email" of relation "users" violates not-null constraint (SQLSTATE 23502) – Exorbitance

This works for sqllite but mysql throws an error that Error 1067 (42000): Invalid default value for – Subbasement

Answer 2

type User struct {
    gorm.Model
    Email  string    `gorm:"unique;not null;type:varchar(100);default:null"`

}

When I use like this it works but when I automigrate I did had error from migration gorm

Subsequence

Answer is a comment on another answer – Poland

This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review – Braque

Answer 3

Add a isValid() function to your model that returns false if a not null field is in its defalt (0 for int, "" for string, etc), and before insert, check if valid, return an error if not valid, else, nil.

Assiduous

Answer 4

A reasonable approach is using a BeforeCreate hook to validate the Email field and return an error if it is empty string. This way, you can ensure that object is only created when the required fields are properly populated.

// BeforeCreate hook to validate email field
func (u *User) BeforeCreate(tx *gorm.DB) (err error) {
    if u.Email == ""  {
        return errors.New("email cannot be empty")
    }
    return nil
}

Gotland