On Thursday, November 1, 2018 at 3:56:30 PM UTC-7, cvss wrote:
>
> I have a model called Test
>
> class Test < Sequel::Model
>
>
> dataset_module do
> def a
> where{...}
> end
>
>
> def b
> where{...}
> end
>
>
> def c
> where{...}
> end
> end
> end
>
> I want to create a fourth dataset combining a and b. Apparently
> def c
> (a & b) | c
> end
>
> in dataset_module returns a Sequel::SQL::BooleanExpression object.
> I want to be able to retrieve combined scope records without having to
> rewrite the queries in each case.
> Am I able to do something like this in Sequel ?
>
You want the subset_conditions plugin:
class Test < Sequel::Model
plugin :subset_conditions
dataset_module do
where :a, :a=>1
where :b, :b=>2
where :c, :c=>3
def abnotc
where((Sequel[a_conditions] & b_conditions) | c_conditions)
end
end
end
The reason you can't do `where((a & b) | c)` is because a, b, and c return
datasets, not boolean expressions, and you use & (AND) and | (OR) to join
boolean expressions together.
AND and OR aren't defined on queries in SQL. If you have three queries,
and you want the combine them in the way you describe, in SQL you need to
use INTERSECT (~AND) and UNION (~OR), which Sequel supports:
def abnotc
a.intersect(b).union(c)
end
Thanks,
Jeremy
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