Allow the use of enums (#168)

spec/database_spec.cr

@@ -8,7 +8,7 @@ describe DB::Database do
 
       db.setup_connection do |cnn|
         cnn_setup += 1
-        cnn.scalar("1").should eq "1"
+        cnn.scalar("a").should eq "a"
       end
 
       cnn_setup.should eq(2)

spec/dummy_driver.cr

@@ -187,7 +187,7 @@ class DummyDriver < DB::Driver
         return (@statement.as(DummyStatement)).params[0]
       end
 
-      return n
+      n.to_i64? || n
     end
 
     def next_column_index : Int32

spec/serializable_spec.cr

@@ -81,6 +81,29 @@ class ModelWithJSON
   property c1 : String
 end
 
+struct ModelWithEnum
+  include DB::Serializable
+
+  getter c0 : Int32
+  getter c1 : MyEnum
+  # Ensure multiple enum types work together
+  getter c2 : MyOtherEnum
+
+  enum MyEnum
+    Foo  = 0
+    Bar  = 1
+    Baz  = 2
+    Quux = 3
+  end
+
+  enum MyOtherEnum
+    OMG
+    LOL
+    WTF
+    BBQ
+  end
+end
+
 macro from_dummy(query, type)
   with_dummy do |db|
     rs = db.query({{ query }})
@@ -172,6 +195,17 @@ describe "DB::Serializable" do
     expect_model("1,a", ModelWithJSON, {c0: 1, c1: "a"})
   end
 
+  it "should initialize a model with an enum property" do
+    expect_model("1,2,LOL", ModelWithEnum, {
+      c0: 1,
+      c1: ModelWithEnum::MyEnum::Baz,
+      c2: ModelWithEnum::MyOtherEnum::LOL,
+    })
+    expect_raises DB::MappingException, "Unknown enum ModelWithEnum::MyEnum value: adsf" do
+      from_dummy("1,adsf,BBQ", ModelWithEnum)
+    end
+  end
+
   it "should initialize multiple instances from a single resultset" do
     with_dummy do |db|
       db.query("1,a 2,b") do |rs|

src/db/result_set.cr

@@ -96,6 +96,23 @@ module DB
       end
     end
 
+    # Read the value based on the given `enum` type, supporting both string and
+    # numeric column types.
+    #
+    # ```
+    # enum Status
+    #   Pending
+    #   Complete
+    # end
+    #
+    # db.query "SELECT 'complete'" do |rs|
+    #   rs.read Status # => Status::Complete
+    # end
+    # ```
+    def read(type : Enum.class)
+      type.new(self)
+    end
+
     # Reads the next columns and returns a tuple of the values.
     def read(*types : Class)
       internal_read(*types)
@@ -135,3 +152,24 @@ module DB
     # end
   end
 end
+
+struct Enum
+  def self.new(rs : DB::ResultSet) : self
+    index = rs.next_column_index
+
+    case value = rs.read
+    when String
+      parse value
+    when Int
+      from_value value
+    else
+      raise DB::ColumnTypeMismatchError.new(
+        context: "#{self}.new(rs : DB::ResultSet)",
+        column_index: index,
+        column_name: rs.column_name(index),
+        column_type: value.class.to_s,
+        expected_type: "String | Int",
+      )
+    end
+  end
+end