Datetime precision breaks autoUpdateTime:nano

[pboguslawski]

Description

Column defined with

ModTime      int64       `gorm:"column:mod_time;not null;autoUpdateTime:nano;index:,composite:mod_time"`

is populated correctly with nano timestamps in sqlite3 but in mysql values are rounded to ms i.e. you get 1689751262515000000 instead of 1689751262515828345 in mysql column.

Workaround that works for us is to set datetimePrecision = 9 or force NowFunc i.e.

&gorm.Config{
 NowFunc: func() time.Time {
    return time.Now() // Here we use monotonic clock to avoid clock synchronization diffs see https://pkg.go.dev/time#hdr-Monotonic_Clocks
},
})

Adding ;precision:9 nor ;precision=9 field tag to ModTime column definition as above does not work.

Datetime precision logic should not be used probably for autoCreateTime nor autoUpdateTime columns because it defines time resolution on its own.