Adding new PG extension for auto converting Numeric to Float. Fixes #955

 (#958)

spec/avram/custom_sql_spec.cr

@@ -0,0 +1,10 @@
+require "../spec_helper"
+
+describe "Custom SQL" do
+  describe "PG::NumericFloatConverter extension" do
+    it "converts PG::Numeric to Float64" do
+      PriceFactory.create(&.in_cents(399).line_item_id(LineItemFactory.create.id))
+      CustomPriceQuery.total.should eq(3.99)
+    end
+  end
+end

spec/support/queries/custom_price_query.cr

@@ -0,0 +1,20 @@
+class CustomPriceQuery
+  class Result
+    include DB::Serializable
+
+    @[DB::Field(converter: PG::NumericFloatConverter)]
+    property total : Float64
+  end
+
+  def self.total : Float64
+    query = <<-SQL
+    SELECT SUM(in_cents) / 100.0 AS total
+    FROM prices
+    SQL
+
+    # Using `query_all` instead of scalar in order to map to
+    # the `CustomPriceQuery::Result` object instead of straight to Float64
+    result = TestDatabase.query_all(query, as: CustomPriceQuery::Result).first
+    result.total
+  end
+end

src/avram.cr

@@ -9,6 +9,7 @@ require "uuid"
 require "cadmium_transliterator"
 
 require "./ext/db/*"
+require "./ext/pg/*"
 require "./avram/object_extensions"
 require "./avram/criteria"
 require "./avram/type"

src/ext/pg/numeric_float_converter.cr

@@ -0,0 +1,12 @@
+# Extends the PG shard and adds a converter for
+# converting `PG::Numeric` columns to `Float64`. This
+# can be used with raw SQL queries.
+# ```
+# @[DB::Field(converter: PG::NumericFloatConverter)]
+# property average_amount : Float64
+# ```
+module PG::NumericFloatConverter
+  def self.from_rs(rs : DB::ResultSet)
+    rs.read(PG::Numeric).to_f
+  end
+end