[Qgis-developer] Built-in attribute form validation

[bernhard.stroebl at jena.de]

Nathan,

I do like your idea, it in fact would reduce the need for custom Uis. 
How about saving the check as part of the project or qml file similar to 
the edit-widget option in the layer properties. Because for my feeling 
that would be the place where it belongs and I cannot be sure that 
anyone loading my qml file has the python file available in the same 
path as I do.
Probably there is only a limited number of checks which cover the 
majority of use cases e.g.
- NOT NULL
- range (for Numbers)
- range (for dates)
- max length (for strings)
- contains regex/string (for strings)
Multiple rules could be applied to any field in the fields tab of the 
layer properties. For special cases you would still need a custom Ui, 
though.

just my two cents

Bernhard



Am 20.12.2011 12:41, schrieb Nathan Woodrow:
> Hi all,
>
> I have been working on this idea over the last couple days which I think
> would be cool/handy to have in QGIS and I would be interested to get some
> feedback with what people think.
>
> The general idea is to add a form of field validation to the built-in
> attribute forms.  The use case for this is pretty clear I think, being able
> to let the user/admin of any layer define validation rules to check against
> the data entered on the attribute form when the user presses OK providing
> instant feedback.  I normally do this on my PostGIS tables but you don't
> get errors until you try and commit the data and even then it's a simple
> "there is a error", if you have added more then 1 item you have to check
> each one to work out what is wrong, and this method only applies to a
> PostGIS layer.  The idea I have been drafting would work on any layer, as
> it's at the QGIS level vs at the datasource level.
>
> My idea is to use simple a simple Python file with basic functions that
> will be called for each field in the attribute form that is editable.  I'm
> a big fan of convention over configuration so my idea uses conventions to
> define what functions are used to validate what fields.  The function will
> return False and an error message that can be shown to the user if
> something is wrong.
>
> The functions use the following syntax: validate{FieldName} or
> validate{FieldIndex} for naming (plus some other styles) e.g
>
> def validateName():
>     if value == "":
>        return (False,"Name can't be NULL")
>     return True
>
> You would place the function in a python file e.g PeopleRules.py and then
> tell QGIS to use this file to look for validation rules, pretty much the
> same as we do now for having custom Python forms.
>
> Overview of logic:
>
>     1. Define Python file with rules
>     2. Tell QGIS to use the rules file for the layer.
>     3. Open attribute form
>     4. Edit some values
>     5. Press OK
>     6. QGIS calls each function in the rules file to validate each field
>     that is defined with a rule
>     7. If there are errors: cancel the accept() action and show the errors.
>      If there are no errors go though like normal.
>
> My thoughts for using Python are:
>
>     - Easy to read and write
>     - Not limited to what we have in QgsExpression and easier to expand.
>     - Can add documentation to validation rules.
>     - Can add more complex validation rules e.g. regex, parsing, database
>     checks etc
>
> My overall goal with this is to reduce the need to create custom Python Qt
> forms when doing data entry, and doing validation is one of the reasons I
> tend to make custom Python Qt forms but then you loose the ease of QGIS
> doing most of the form work for you.
>
> I have attached two files which have a example of what the idea is.
>   fieldChecks.py is an example rules file with comments to explain each
> section, runMe.py has the logic for reading and executing the rules for
> each field.  Run: python runMe.py to see the running logic and output.
>
> What love to get peoples thoughts about this, users and devs a like.
>
> - Nathan
>
>
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