Custom Array Converters

[zbaylin]

If I have a class Circle and a model Shapes, if I define a custom converter for Circle (CircleConverter) and do this:

class Shapes
  ...
  column circles : Array(Circle)
  ...
end

I get this error: Error: No converter found for Array(Circle).

How do I convert arrays of custom types/classes?

[anykeyh]

Hi,

You cannot use directly your circle converter with Array(Circle) because the way array is encoded might be different based on your implementation. You need to create a converter for Array(Circle) and add it like this:

Clear::Model::Converter.add_converter("Array(Circle)", ArrayCircleConverter)

[zbaylin]

How do you go about doing this? I have the Circle encoded as TEXT in the DB

[anykeyh]

I'm not sure about your data, but first you need to figure out what kind of data the pg gems detect.
It might be Slice or already Array(::PG::StringArray)

For that you can try a simple Select query like this:

# Assuming your column is living in models.circles
# I've not run this code so it might have some typo or errors :)
value = Clear::SQL.select.from("models").pluck_col("circles")
puts values.class.name
puts values

After that, just build your converter, based on the output you got; assuming it's a Array(::PG::StringArray) for example (code not tested but you get the idea):

module ArrayCircleConverter
  def self.to_column(x) : Array(Circle)?
    return nil unless x
    
    case x
    when ::Array(::PG::StringArray)
      return x.map{ |circle| CircleConverter.to_column(circle.to_s) } # Tricky `to_s` call here: circle could be a nested array but don't want to care about it.
    else
      raise "Cannot convert from #{x.class} to Array(Circle)"
    end
  end

  def self.to_db(arr : Array(Circle)? ) : Clear::SQL::Any
    return nil unless x
    arr.map do |c|
      Clear::Expression.unsafe({"Array[", CircleConverter.to_db(c), "]"}.join)
    end
  end

end

[zbaylin]

With some tweaking I got this to work, thanks!