Converters

Any type from PostgreSQL can be converted using converter objects. By default, Clear converts already the main type of PostgreSQL.

However, custom type may not be supported yet. Clear offers you the possibility to add a custom converter.

Declare a new converter

The example below with a converter for a Color structure should be straight-forward:

require "./base"
struct MyApp::Color
property r : UInt8 = 0
property g : UInt8 = 0
property b : UInt8 = 0
property a : UInt8 = 0
def to_s
# ...
end
def self.from_string(x : String)
# ...
end
def self.from_slice(x : Slice(UInt8))
# ...
end
end
class MyApp::ColorConverter
def self.to_column(x) : MyApp::Color?
case x
when Nil
nil
when Slice(UInt8)
MyApp::Color.from_slice(x)
when String
MyApp::Color.from_string(x)
else
raise "Cannot convert from #{x.class} to MyApp::Color"
end
end
def self.to_db(x : MyApp::Color?)
x.to_s #< css style output, e.g. #12345400
end
end
Clear::Model::Converter.add_converter("MyApp::Color", MyApp::ColorConverter)

Then you can use your mapped type in your model:

class MyApp::MyModel
include Clear::Model
#...
column color : Color #< Automatically get the converter
end

converter option

Optionally, you may want to use a converter which is not related to the type itself. To do so, you can pass the converter name as optional argument in the column declaration:

class MyApp::MyModel
include Clear::Model
#...
column s : String, converter: "my_custom_converter"
end

By convention, converters which map struct and class directly are named using CamelCase, while converters which are not automatic should be named using the underscore notation.