Deprecate `primaryKey` in favour of `primaryKeys`

[peterdesmet]

For consistency, I think we should deprecate primaryKey in favour of primaryKeys:

I notice myself typing primaryKeys (plural), forgetting that is not a property of Table Schema.

[khusmann]

Hmmm isn't it more correct in the singular? Although the primary key for a table may be determined by multiple fields, there is only one primary key definition per table. Whereas many foreign key and unique key definitions can exist simultaneously in a given table, so the plural there makes sense.

I'm less familiar with DB design so maybe I'm missing something?

[roll]

I think I mentioned it a somewhere during the v2 work but I see it this way as it was designed after data base design:

primaryKey: array
uniqueKeys: array of arrays
foreignKeys array of arrays

In this terminology key = list of fields and keys = multiple lists of fields

[peterdesmet]

Makes sense, but isn't uniqueKeys and array just like primaryKey?

[roll]

No, array of arrays https://datapackage.org/standard/table-schema/#uniqueKeys - so it's possible to define multiple unique combinations