graphql: Filtering by a constant(s)

[Aklakan]

While it is possible to use the generic sparql inject mechanism to filter fields, there should also be one that works on simple strings - even if those introduce ambiguity.

{
  myField @sparql(inject: "FILTER(?s = <urn:foo:bar>)")
}

Consider the following example:

{
  myField @filter(value: "http://foobar")
}

It could in a first step be translated generically into

FILTER(?s = <http://foobar> || ?s = "http://foobar")

Afterwards, we can apply value space analysis, which might detect that e.g. ?s appears only in the subject position and thus cannot be a string, leading to the opportunity to eliminate the string comparison.

The same approach could be used for @filter(in: ["urn:some", "http://array", "of values"]).