How to manage constraint and represent mutilple values in the same field

[demeringo]

Some fields may allow multiple values (e.g. the environmental_indicators column may need to accept several environmental indicators).

We need to understand how to represent this in the frictionless table schema. https://specs.frictionlessdata.io/table-schema/

We can already apply constraint the values of unitary fileds by using enums in the schema. But we may need to find a different way to model fields that have multiple values (i.e. collection / arrays)

💡 If this is too complex to model, edit or validate, an alternative would be to add more columns, one for each indicator and use it a a boolean (true/false) colum.

[demeringo]

https://github.com/frictionlessdata/datapackage/pull/38/files/3c2a9b421a967b638c27316b47f9302914b5ce97#diff-85c641a79af3c7529a7f7ab6b850399e37c504fe44516add84d7b4f5a6c39049

[demeringo]

The answer depends on the context !

When validating the data:

1. The field has to be modeled as a String.
2. We decide to use a custom separator (e.g. + or |char) between values
3. We use a custom validation pattern (regexp) to validate the content

See

ict-sustainability-tools/old-examples/project-list/data/project-list.resources.yaml

Line 39 in ebf0092

constraints:

When displaying / editing the data in the widget:

1. We declare the field (and its allowed values) as a string with an enum constraint in the table-schema .

   ict-sustainability-tools/old-examples/project-list/model/project-list.frictionless-table-schema.json

   Line 27 in ebf0092

   "constraints": {

2. We define the type of the field as tags (⚠ plural form) instead of tag (singular) in the widget config (custom field properties)

   ict-sustainability-tools/old-examples/project-list/widget/project-list.fields-custom-properties.json

   Line 19 in ebf0092

   "subtype": "tags",

3. We explicit the choosen separator in the widget config (custom field properties) We define the type of the field as tags (⚠ plural form) instead of tag (singular) in the widget config (custom field properties)

   ict-sustainability-tools/old-examples/project-list/widget/project-list.fields-custom-properties.json

   Line 20 in ebf0092

   "tagSeparator": "+"

[demeringo]

💡 Close this issue only after our choices of implementation are fully reported into the documentation.