feat: PG::Numeric to Float64 field converter

spec/migration.sql

@@ -2,6 +2,7 @@
 
 DROP TABLE IF EXISTS posts;
 DROP TABLE IF EXISTS users;
+DROP TABLE IF EXISTS pg_numeric_model;
 
 CREATE TABLE users(
   id          SERIAL PRIMARY KEY,
@@ -20,3 +21,8 @@ CREATE TABLE posts(
   created_at  TIMESTAMPTZ NOT NULL,
   updated_at  TIMESTAMPTZ
 );
+
+CREATE TABLE pg_numeric_model(
+  id        SERIAL PRIMARY KEY,
+  a_number  NUMERIC(16, 8)
+)

spec/model/converters/db/pg/numeric_spec.cr

@@ -0,0 +1,24 @@
+require "../../../../spec_helper"
+require "../../../../../src/core/model/converters/db/pg/numeric"
+
+require "pg"
+
+db = DB.open(ENV["DATABASE_URL"] || raise "No DATABASE_URL is set!")
+query_logger = Core::QueryLogger.new(nil)
+repo = Repo.new(db, query_logger)
+
+class PGNumericModel < Core::Model
+  schema do
+    table_name "pg_numeric_model"
+    primary_key :id
+    field :a_number, Float64, db_converter: Converters::DB::PG::Numeric
+  end
+end
+
+describe Core::Model::Converters::DB::PG::Numeric do
+  repo.insert(PGNumericModel.new(a_number: 42.0))
+
+  it do
+    repo.query(Query(PGNumericModel).all).first.a_number.should be_a(Float64)
+  end
+end

src/core/model/converters/db/pg/numeric.cr

@@ -0,0 +1,34 @@
+require "../converter"
+require "pg/numeric"
+
+module Core
+  abstract class Model
+    module Converters::DB
+      # Allows to represent `PG::Numeric` values as `Float64`s in `Model`s.
+      #
+      # ```
+      # # SQL:
+      # # table users
+      # #   column balance NUMERIC(16, 8)
+      #
+      # require "core/model/converters/db/pg/numeric"
+      #
+      # class User < Core::Model
+      #   schema do
+      #     field :balance, Float64, db_converter: Converters::DB::PG::Numeric
+      #   end
+      # end
+      #
+      # user = repository.query(Query(User).last).first
+      # user.balance # => 42.0
+      # ```
+      module PG
+        class Numeric < Converter(::PG::Numeric)
+          def self.from_rs(rs)
+            rs.read(::PG::Numeric | Nil).try &.to_f64
+          end
+        end
+      end
+    end
+  end
+end