[Qgis-user] Conditional Value Mapping
ALT SHN
i.geografica at alt-shn.org
Thu Apr 23 05:06:47 PDT 2015
Muchas Gracias Victor!
I thought about something of that sort, but in my case having data in a
database is not an option.
Anyway your solution seems to work, I'll keep it for future reference.
Regards,
Andre
2015-04-23 14:00 GMT+02:00 Víctor Manuel Herreros Villanueva <
vherreros at ucm.es>:
> Dear André,
>
> I asked for the same problem months ago without obtaining any answer. As
> far as I know, there is no QGIS feature implemented that allows you to
> achieve what you are looking for.
>
> So I decided to dive into my underlying PostgreSQL databse structure. The
> solution I chose was the following: Two reference tables with data
> description and one table with data for the user affected by one constraint.
>
> *Reference table for attribute 1 (ATTR1_TABLE)*
> -- ----------------
> ID Textf
> -- ----------------
> 01 Agriculture (01)
> 02 Forest (02)
> -- ----------------
>
> *Reference table for attribute 2 (ATTR2_TABLE)*
> ----- --------------
> ID Textf
> ----- --------------
> 01.01 Corn (01.01)
> 01.02 Wheat (01.02)
> 02.01 Pines (02.01)
> 02.02 Olives (02.02)
> ----- --------------
>
> *Structure of the table containing the data to be shown to the final user
> (DATA_TABLE)*
> attrib1_cod: character varying(9)
> attrib1_desc: character varying(100)
> attrib2_cod: character varying(9)
> attrib2_desc: character varying(100)
>
> Then I stablished the appropriate *database constraint*:
>
> ALTER TABLE DATA_TABLE
> ADD CONSTRAINT data_table_cc_attr2 CHECK (attrib2_cod IS NULL OR
> attrib2_cod::text = ''::text OR "substring"(attrib2_cod::text, '^..'::text)
> = attrib1_cod::text);
>
> With this constraint, you ensure that the data to be introduced in
> ATTR2_TABLE ID field must contain in the string beginning one of the values
> present in ATTRIB1_TABLE ID field. So, if your user has selected
> attrib1_cod/attrib1_desc 01/Agriculture (01) for DATA_TABLE, then, when
> fullfilling attrib2_cod field he only can choose the values 01.01 or 01.02,
> because both of them start with the string '01'.
>
> Well, he can really choose any value for attrib2_cod, but only the
> appropriate ones won't throw insertion errors.
>
> The problem with this workaround is that the user can choose any value for
> attr2_cod field. But, if you decide to show him just the descriptive text
> fields, he can easily see which ones are proper values (because in the tex
> field all records end with the numeric code).
>
> I've personally decided to use just the numeric values for my users. So,
> under QGIS, and through a widget (value map), I show my users the fields
> attrib1_cod and attrib2_cod, but with the values taken from the text fields:
>
> *Value map widget for attrib1_cod*
> ----- ----------------
> Value Description
> ----- ----------------
> 01 Agriculture (01)
> 02 Forest (02)
> -- ----------------
>
> When the user selects from the drop down list the description 'Agriculture
> (01)', he is really selecting the value '01' for attrib1_cod. The same
> applies to attrib2_cod:
>
> *Value map widget for attrib2_cod*
> ----- --------------
> Value Description
> ----- --------------
> 01.01 Corn (01.01)
> 01.02 Wheat (01.02)
> 02.01 Pines (02.01)
> 02.02 Olives (02.02)
> ----- --------------
>
> And finally, in order not to ask the user to fullfill the field
> attrib*_desc (cause he has previously fullfilled attrib*_cod but from
> descriptive values), I have two more triggers and trigger functions whose
> mission is to fill in the descriptive fields provided the code fields have
> been modified:
>
> *Trigger for attrib1_desc on table DATA_TABLE*
> CREATE TRIGGER update_attrib1_desc
> BEFORE INSERT OR UPDATE
> ON DATA_TABLE
> FOR EACH ROW
> EXECUTE PROCEDURE update_attrib1_desc();
>
> *Trigger function for called by the previous trigger*
> CREATE OR REPLACE FUNCTION update_attrib1_desc()
> RETURNS trigger AS
> $BODY$
> DECLARE
> BEGIN
> IF (TG_OP = 'INSERT' OR TG_OP = 'UPDATE' ) THEN
> NEW.attrib1_desc := (SELECT Textf FROM ATTR1_TABLE WHERE ID =
> NEW.attrib1_cod);
> RETURN NEW;
> ELSE
> RETURN NULL;
> END IF;
> END;
> $BODY$
> LANGUAGE plpgsql VOLATILE
> COST 100;
>
> So each time an attrib1_cod field is entered or updated, the trigger seeks
> for the appropriate attrib1_desc field and writes it into attrib1_desc
> field.
>
> And the same for attib2_desc:
>
> *Trigger for attrib2_desc on table DATA_TABLE*
> CREATE TRIGGER update_attrib2_desc
> BEFORE INSERT OR UPDATE
> ON DATA_TABLE
> FOR EACH ROW
> EXECUTE PROCEDURE update_attrib2_desc();
>
> *Trigger function for called by the previous trigger*
> CREATE OR REPLACE FUNCTION update_attrib2_desc()
> RETURNS trigger AS
> $BODY$
> DECLARE
> BEGIN
> IF (TG_OP = 'INSERT' OR TG_OP = 'UPDATE' ) THEN
> NEW.attrib2_desc := (SELECT Textf FROM ATTR2_TABLE WHERE ID =
> NEW.attrib2_cod);
> RETURN NEW;
> ELSE
> RETURN NULL;
> END IF;
> END;
> $BODY$
> LANGUAGE plpgsql VOLATILE
> COST 100;
>
>
> A little bit confusing, but I haven't found any other way to solve the
> problem...
>
> Best regards.
>
>
>
> 2015-04-23 12:19 GMT+02:00 ALT SHN <i.geografica at alt-shn.org>:
>
>> Hi,
>>
>> I am looking for a way to implement conditional value mapping in QGIS.
>> This means that the values available in attribute number 2 depend on the
>> value provided in attribute 1.
>>
>> Example:
>>
>> If the user enters "agriculture" in attribute 1, for attribute 2 only
>> "corn" or "wheat" will be available.
>>
>> Instead, if the user enters "forest" in attribute 1, for attribute 2 only
>> "pines" or "olives" will be available.
>>
>> And so on...
>>
>> Apparently this is not doable just using the QGIS widget expression
>> builder, but I am not sure. Here's a screencast to help visualize. The
>> problem is that if for "class" I pick other than "Agri_Field", for the
>> "color_aggri" attribute the same possible values appear.
>>
>> [image: enter image description here]
>>
>> Thanks in advance for any hints!
>>
>>
>> Regards,
>>
>>
>> Andre
>>
>>
>>
>>
>> --
>> ---------------------------------------------------------------
>>
>>
>> *Sociedade de História Natural*
>> Departamento de Informação Geográfica
>> Polígono Industrial do Alto do Amial
>> Pav.H02 e H06
>>
>> i.geografica at alt-shn.org <laboratorio at alt-shn.org>
>> www.shn.pt
>> www.alt-shn.blogspot.com
>> Facebook <https://www.facebook.com/SociedadeDeHistoriaNatural?ref=hl>
>>
>> TLM: 964138188
>>
>>
>> _______________________________________________
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>> http://lists.osgeo.org/mailman/listinfo/qgis-user
>>
>
>
>
> --
>
> <http://www.ucm.es/> *Universidad Complutense de Madrid*
> <http://www.ucm.es/> Dr. *Víctor Manuel Herreros Villanueva*
> Jefe de Proyecto
> *Gestión de EspaciosData Warehouse*
> Jardín Botánico
> Av. Complutense s/n
> 28040 Madrid
> *Tfn. (+34) 91 394 7275 Fax. (+34) 91 394 4773* vherreros at ucm.es
>
>
>
> _______________________________________________
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>
--
---------------------------------------------------------------
*Sociedade de História Natural*
Departamento de Informação Geográfica
Polígono Industrial do Alto do Amial
Pav.H02 e H06
i.geografica at alt-shn.org <laboratorio at alt-shn.org>
www.shn.pt
www.alt-shn.blogspot.com
Facebook <https://www.facebook.com/SociedadeDeHistoriaNatural?ref=hl>
TLM: 964138188
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