Allow precision option for postgresql datetimes

This patch addresses the difficulty of retrieving datetime fields. By default, the database holds a higher precision than the time as a String.

This issue is discussed at length at the following links:
- [#3519](https://github.com/rails/rails/issues/3519)
- [#3520](https://github.com/rails/rails/issues/3520)

Also, kudos to @mattscilipoti

1 files changed, 65 insertions, 0 deletions

diff --git a/activerecord/test/cases/adapters/postgresql/timestamp_test.rb b/activerecord/test/cases/adapters/postgresql/timestamp_test.rb
index 337f43c421..26507ad654 100644
--- a/activerecord/test/cases/adapters/postgresql/timestamp_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/timestamp_test.rb
@@ -27,4 +27,69 @@ class TimestampTest < ActiveRecord::TestCase
     d = Developer.create!(:name => 'aaron', :updated_at => -1.0 / 0.0)
     assert_equal(-1.0 / 0.0, d.updated_at)
   end
+
+  def test_default_datetime_precision
+    ActiveRecord::Base.connection.create_table(:foos)
+    ActiveRecord::Base.connection.add_column :foos, :created_at, :datetime
+    ActiveRecord::Base.connection.add_column :foos, :updated_at, :datetime
+    assert_nil activerecord_column_option('foos', 'created_at', 'precision')
+  end
+
+  def test_timestamp_data_type_with_precision
+    ActiveRecord::Base.connection.create_table(:foos)
+    ActiveRecord::Base.connection.add_column :foos, :created_at, :datetime, :precision => 0
+    ActiveRecord::Base.connection.add_column :foos, :updated_at, :datetime, :precision => 5
+    assert_equal 0, activerecord_column_option('foos', 'created_at', 'precision')
+    assert_equal 5, activerecord_column_option('foos', 'updated_at', 'precision')
+  end
+
+  def test_timestamps_helper_with_custom_precision
+    ActiveRecord::Base.connection.create_table(:foos) do |t|
+      t.timestamps :precision => 4
+    end
+    assert_equal 4, activerecord_column_option('foos', 'created_at', 'precision')
+    assert_equal 4, activerecord_column_option('foos', 'updated_at', 'precision')
+  end
+
+  def test_passing_precision_to_timestamp_does_not_set_limit
+    ActiveRecord::Base.connection.create_table(:foos) do |t|
+      t.timestamps :precision => 4
+    end
+    assert_nil activerecord_column_option("foos", "created_at", "limit")
+    assert_nil activerecord_column_option("foos", "updated_at", "limit")
+  end
+
+  def test_invalid_timestamp_precision_raises_error
+    assert_raises ActiveRecord::ActiveRecordError do
+      ActiveRecord::Base.connection.create_table(:foos) do |t|
+        t.timestamps :precision => 7
+      end
+    end
+  end
+
+  def test_postgres_agrees_with_activerecord_about_precision
+    ActiveRecord::Base.connection.create_table(:foos) do |t|
+      t.timestamps :precision => 4
+    end
+    assert_equal '4', pg_datetime_precision('foos', 'created_at')
+    assert_equal '4', pg_datetime_precision('foos', 'updated_at')
+  end
+
+  private
+
+    def pg_datetime_precision(table_name, column_name)
+      results = ActiveRecord::Base.connection.execute("SELECT column_name, datetime_precision FROM information_schema.columns WHERE table_name ='#{table_name}'")
+      result = results.find do |result_hash|
+        result_hash["column_name"] == column_name
+      end
+      result && result["datetime_precision"]
+    end
+
+    def activerecord_column_option(tablename, column_name, option)
+      result = ActiveRecord::Base.connection.columns(tablename).find do |column|
+        column.name == column_name
+      end
+      result && result.send(option)
+    end
+
 end