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Unable to Use String Type as sql.NullString
When creating a GORM model, you may encounter an error if you try to use a string type for a field that needs to be nullable. The issue arises when using sql.NullString for nullable fields.
Problem:
The error you're getting, "cannot use "a string goes here", (type string) as type sql.NullString in field value," indicates that you're trying to assign a string directly to a sql.NullString field. However, sql.NullString is not a string type, but a struct type designed to represent nullable strings.
Solution:
To resolve this issue, you need to initialize the sql.NullString field correctly. It should be initialized as:
<code class="go">db.Create(&Day{ Nameday: "Monday", Dateday: "23-10-2019", Something: sql.NullString{String: "a string goes here", Valid: true}, Holyday: false, })</code>
Alternative Solution:
If you prefer using a simplified syntax for nullable strings, you can create your own nullable string type by implementing the sql.Scanner and driver.Valuer interfaces, and leveraging the null byte to signal a NULL value.
<code class="go">type MyString string const MyStringNull MyString = "\x00" // implements driver.Valuer, will be invoked automatically when written to the db func (s MyString) Value() (driver.Value, error) { if s == MyStringNull { return nil, nil } return []byte(s), nil } // implements sql.Scanner, will be invoked automatically when read from the db func (s *MyString) Scan(src interface{}) error { switch v := src.(type) { case string: *s = MyString(v) case []byte: *s = MyString(v) case nil: *s = MyStringNull } return nil }</code>
With this type, you can initialize the Something field as follows:
<code class="go">db.Create(&Day{ Nameday: "Monday", Dateday: "23-10-2019", Something: "a string goes here", Holyday: false, })</code>
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