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Fluree database library
https://fluree.github.io/db/
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SPARQL VALUES patterns #769

Closed dpetran closed 3 months ago

dpetran commented 4 months ago

In SPARQL, a VALUES pattern can appear inside a WHERE clause alongside other patterns. In FQL :values is its own clause. This mismatch makes translating directly awkward, since we need to insert our translated pattern at a different point in the parse tree than where we are at translation time.

We got around it by translating it into a :bind pattern. However, a :bind pattern can only bind a single value to a variable, so we limited the scope of a VALUES pattern to only a single value.

This gets around it by "tagging" the translated value pattern and then after the whole parsing is done, moving it to the correct place in the tree: see format-values. It's awkward, but it gives much more flexibility to the user.

bplatz commented 4 months ago

Should we move :values into the where clause? I'd imagine it is there because there could be multiple where clauses, or sub-queries which might have its own set of values.

dpetran commented 4 months ago

It's not a bad idea, and it clearly works for SPARQL. I don't think it would be too complex to support, just a new (defmethod match-pattern :values) that directly injects into the solution-ch, but there may be some finicky bits about pattern ordering. And it would save me from having to rearrange the translated query : )

dpetran commented 4 months ago

Rebased on https://github.com/fluree/db/pull/777

zonotope commented 3 months ago

We got around it by translating it into a :bind pattern. However, a :bind pattern can only bind a single value to a variable, so we limited the scope of a VALUES pattern to only a single value.

:bind patterns can take any number of mappings of values to variables.

dpetran commented 3 months ago

We got around it by translating it into a :bind pattern. However, a :bind pattern can only bind a single value to a variable, so we limited the scope of a VALUES pattern to only a single value.

:bind patterns can take any number of mappings of values to variables.

Right, maybe it is better stated that a :bind pattern can only bind a single value per variable, whereas :values can bind multiple values per variable.

dpetran commented 3 months ago

Rebased on https://github.com/fluree/db/pull/777