Building a dynamic query using recursion

Questions & Help Questions
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2

I interpret that document as describing a different structure where both and and or take the terms they apply to in a list. For your example, start by writing the expression with explicit parentheses:

(a == 1 and (b == 4 and c == 3)) or (d == 2)

Rules:

  • %{variable_name: %{eq: value}} corresponds to variable_name == value
  • %{var1: %{eq: v1}, var2: %{eq: v2}} corresponds to (var1 == v1) and (var2 == v2)
  • %{and: [X, Y, Z]} corresponds to the expression (X and (Y and Z))
  • %{or: [X, Y, Z]} corresponds to the expression (X or (Y or Z))

so

%{
  a: %{eq: 1},
  b: %{eq: 4},
  c: %{eq: 3}
}

corresponds to (a == 1 and (b == 4 and c == 3)). So finally

%{
  or: [
    %{
      a: %{eq: 1},
      b: %{eq: 4},
      c: %{eq: 3}
    },
    %{
      d: %{eq: 2}
    }
  ]
}

corresponds to the original expression.

The recursion you’ll need to turn the map above into Ecto operations is the derivation in reverse. You’ll likely want to use explicit recursion for this, as it’s a depth-first traversal of the input.