In QGIS, there is this nice tool "Refactor Fields" in the Processing Toolbox :

Refactor Fields tool

Using it on a single layer is fairly straightforward.

However, when you plan on using it in a batch mode, one can see the "Fields mapping" textbox. I'm looking for an example of the syntax to be used there. I haven't found any specific documentation yet.

Refactor batched

  • After run a refactoring from the GUI, you can watch the command in the Processing -> History menu (Ctrl+Alt+H)
    – kadarivan
    Jul 17, 2018 at 6:02

2 Answers 2


It is not very comfortable to do, but the following is the required syntax for that textbox (I write it in several lines only for the sake of clearness):

{'expression': u'type the expression here',
 'length': <type the length>,
 'type': <code of the type>,
 'name': u'type the field name here',
 'precision': <type the precision>}

For example (remeber to use curly brackets):

{'expression': u'"FLAG1"+"FLAG2"',
 'length': 20, 'type': 6,
 'name': u'FLAG1',
 'precision': 5}

You need to write as many lines like the one above as the number of input fields, separated by commas. For example, if your layer contains three fields:

{'expression': u'"FLAG1"+"FLAG2"', 'length': 20, 'type': 6, 'name': u'FLAG1', 'precision': 5}, {'expression': u'100*"FLAG2"', 'length': 20, 'type': 6, 'name': u'FLAG2', 'precision': 5}, {'expression': u'"100-"FLAG2"', 'length': 20, 'type': 6, 'name': u'FLAG3', 'precision': 5}

and it should work (it worked for me).

Please note that you may avoid to use this dictionary-oriented syntax and directly use the required values. For example, with reference to the first example, you may simply use:

{u'"FLAG1"+"FLAG2"', 20, 6, u'FLAG1', 5}

If you don't use this syntax, the following error will be shown:

Missing parameter value: Fields mapping (row 1)

  • 2
    Can you please explain what <code of the type> means? I tried using 3 assuming it is for string (as it is the 3rd in the dropdown options) but I got an error: 'int' object has no attribute 'getItem' See log for more details. The code I used is:{u'"FLAG"', 0, 3, u'FLAG', 0} for one of my layers where {'expression': u'"FLAG"', 'length': 0, 'type': 3, 'name': u'FLAG', 'precision': 0}.
    – JAT86
    Sep 11, 2017 at 8:27
  • @JAT86 It is the number that identifies the data type (i.e. int, string and so on). Unfortunately, I didn't find a reference for them, but I should remember the values for the most used types: 2 for int, 6 for double and 10 for string. In addition to this, maybe you should not specify 0 for the field length (at least 1!). Please, let me know if you solved the issue.
    – mgri
    Sep 11, 2017 at 10:08
  • Thanks for the prompt response. Perhaps the batch processing is much more complex than I had thought. I tried using at least 1 for the length and 10 for type of code: {u'"FLAG"', 1, 10, u'FLAG', 0} Still, the error shows up: 'int' object has no attribute 'getItem' See log for more details. My layer has the following attributes: name: flag,Type: string, Length: 0, Precision: 0, Expression: "flag"
    – JAT86
    Sep 11, 2017 at 12:30
  • @JAT86 Does running the tool from the GUI return any problem?
    – mgri
    Sep 11, 2017 at 14:23
  • If by GUI you mean a single layer, no it did not have any problems. The FLAG column was successfully deleted upon "clicking Delete selected field" and was saved into a new layer "Refactored".
    – JAT86
    Sep 11, 2017 at 19:00

There is another algorithm similar to this whose interface simplifies the batch process better.

enter image description here

  • 1
    English english
    – BERA
    Nov 10, 2017 at 13:44
  • The english translation for the menu item in question is "Add field to attribute table"
    – J. Taylor
    Mar 7, 2018 at 1:49

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