Dynamically build conditions

[MentiHelgi]

Hi. I am struggling with building (recursively) dynamic conditions (they can be nested).

I have a structure, parsed by an external library that looks something like this:

[ 'and', ['eq', 'field', 'value'], ['eq', 'other_field', 'other_value']]

The method I opted for was to do recursion, that is iterate over the array. When I meet a logical operator (and, or, not), I recurse and build the child expressions, which are then returned. This will look something like this:

exp = {
  "and"  => -> (expressions) { Sequel.&(expression) },
  "eq" => -> (field, value) { Sequel.lit("#{field} = ?", value) }
}
... # Array iteration
operator, *expressions = *filters
case op
when "and"
  exp[operator].call(expressions.map { |expression| parse(expression) })
when "eq"
  field, value = *expressions
  exp[operator].call(field, value)
...

The problem is that this only works for value operators. I can't get this to work for logical operators. I would have expected to be able to call some method like Sequel.and that takes an array of expressions and returns a Sequel AND object that would just translate to SQL such as: foo = 'bar' AND baz = 'qux'.

Anyone have any idea what I need to do for AND, OR and NOT to achieve this?

[janko]

It sounds like Sequel.&, Sequel.| and Sequel.~ are the methods you want, you can see their usage in Sequel for SQL Users guide.

[MentiHelgi]

For some reason, when I do that, ie. Sequel.&([Sequel.lit(....), Sequel.lit(...)]) the resulting boolean expression is a :NOOP (ex: WHERE (a = 'b', c = 'd'). Should I be doing: Sequel.&(*expressions) or something like that instead?

[jeremyevans]

Yes. Sequel.& and Sequel.| take multiple arguments and combine them with AND or OR. Passing a single argument returns the argument as-is.

[MentiHelgi]

Great. Thanks for clearing that out! 😸