qgis - How to convert a string field to a date field

I have a layer with points which represent the fatal road accidents and the field "dates_14_D" contains their date but its type is string. I would like to convert this string field to date field but the OK button is inactive. What's the problem? I use QGis. Look the below picture

Answer

I'm surprised I haven't seen this before. Maybe I'm overlooking something obvious :)

Although you're using a different locale to me, you're using the same date format as I do in the UK, dd/MM/yyyy. I get a slightly different error (on QGIS 2.16.1) but it doesn't like that date format.

You can get around this by creating a short python script in the function editor tab of the expression editor.

• Go into the function editor tab in the expression editor


• Create a new function ("New file" button)


• paste the following into the code window. You may get indentation errors, so manually re-indent with spaces if needed


• click on "Load" button to save the changes


• switch back to the expression tab


• look under the python heading, should now see a function called parse_date_dmy

---

from qgis.core import *
from qgis.gui import *

from PyQt4.QtCore import QDate

@qgsfunction(args="auto", group='Python')
def parse_date_dmy(fromval, feature, parent):
    return QDate.fromString(fromval, 'dd/MM/yyyy')

You can then enter an expression like so, using your field name :-

parse_date_dmy("mydate") 

If all is well, you should see something like this...