How to support negated where expression/condition

[brsanthu]

We have been working on a custom SQL DSL that is based off of SQL. That DSL should support negated where expression (not just not in operator) and conditions. Below are some examples that it should support and here is the simplified part playground.

where not id = 'test';

where (not id = 'test');

where (not (id = 'test' and name = 'test'));

where (not (id = 'test' and name = 'test')) or (name = 'test');

I have tried many iterations and I'm not getting where to place that negated expr grammar. We went through the langium-sql where clause but still not getting how to support this type of construct. So far EBNF has been very easy to follow except for where expressions due to its recursive nature.

[msujew]

Hey @brsanthu,

this is effectively just another type of primary expression, see this modified playground example.

[brsanthu]

Thank you, that looks so elegant after we pulling our hair to get it work :).

Can you please explain what does {infer NotExpr} means?

[cdietrich]

it basically means create an instance of NotExpr and infer its type.
see https://langium.org/docs/grammar-language/#simple-actions