How can I read/write an array of objects inside a PostgreSQL row? (GoLang)

I defined this types in GoLang:

type Comment struct {
	Id          int
	User        string
	Email       string
	Date        string
	Comment     string
}

type Post struct {
	Id          int
	Special     bool
	Title       string
	Date        string
	Content     string
	Image       string
	Comments    []Comment
}

I need to know how to modify this code:

OpenDB()
rows, _ := cn.Query(`SELECT id, date, title, special, content, image
			FROM posts ORDER BY date DESC LIMIT $1
			OFFSET $2`, fmt.Sprint(limit), fmt.Sprint(offset))
posts := []Post{}
for rows.Next() {
  post := Post{}
  e := rows.Scan(&post.Id, &post.Date, &post.Title,
				&post.Special, &post.Content, &post.Image)
  if e != nil {
	panic(e)
  }
  posts = append(posts, post)
}

To allow reading comments. And also, how I can modify:

OpenDB()
_, e = cn.Exec(`INSERT INTO
				posts(date, title, special, content, image)
				VALUES ($1, $2, $3, $4, $5)`, date, title, special, content, image)
if e != nil {
	panic(e)
}
defer CloseDB()

To allow writting an empty array of comments.

Finally I would be grateful if someone tell me how can I write single comments into an existing post.

This depends on your database schema.

If Comment has its own table you will have to loop over all comments in a Post and insert them after you have have inserted the Post. cn.Exec should return a Result which can be used to get the last inserted ID like:

result, err := cn.Exec(...)
if err != nil {
  panic(err)
}

id, err := result.LastInsertId()
if err != nil {
  panic(err)
}

You can now use the ID of your post as a foreign key.

If you are using a JSON column to store your comments you should define a custom type as alias for []Comment and make the type implement sql.Scanner and driver.Valuer.

type Comment struct {
    Id          int
    User        string
    Email       string
    Date        string
    Comment     string
}

type Comments []Comment

// Make the Comments type implement the driver.Valuer interface. This method
// simply returns the JSON-encoded representation of the struct.
func (c Comments) Value() (driver.Value, error) {
    return json.Marshal(c)
}

// Make the Comments type implement the sql.Scanner interface. This method
// simply decodes a JSON-encoded value into the struct fields.
func (c *Comments) Scan(value interface{}) error {
    var b []byte
    switch t := value.(type) {
    case []byte:
        b = t
    case string:
        b = string(t)
    default:
        return errors.New("unknown type")
    }

    return json.Unmarshal(b, &c)
}