ActiveRecord support to PostgreSQL 9.2 JSON type

This implements the support to encode/decode JSON
data to/from database and creating columns of type
JSON using a native type [1] supported by PostgreSQL
from version 9.2.

[1] http://www.postgresql.org/docs/9.2/static/datatype-json.html

activerecord/CHANGELOG.md

@@ -14,6 +14,11 @@
 
     *Ian Lesperance*
 
+*   Allow JSON columns to be created in PostgreSQL and properly encoded/decoded
+    to/from database.
+
+    *Dickson S. Guedes*
+
 *   Fix time column type casting for invalid time string values to correctly return nil.
 
     *Adam Meehan*

activerecord/lib/active_record/connection_adapters/column.rb

@@ -124,6 +124,7 @@ def type_cast_code(var_name)
         when :boolean              then "#{klass}.value_to_boolean(#{var_name})"
         when :hstore               then "#{klass}.string_to_hstore(#{var_name})"
         when :inet, :cidr          then "#{klass}.string_to_cidr(#{var_name})"
+        when :json                 then "#{klass}.string_to_json(#{var_name})"
         else var_name
         end
       end

activerecord/lib/active_record/connection_adapters/postgresql/cast.rb

@@ -37,6 +37,22 @@ def string_to_hstore(string)
           end
         end
 
+        def json_to_string(object)
+          if Hash === object
+            ActiveSupport::JSON.encode(object)
+          else
+            object
+          end
+        end
+
+        def string_to_json(string)
+          if String === string
+            ActiveSupport::JSON.decode(string)
+          else
+            string
+          end
+        end
+
         def string_to_cidr(string)
           if string.nil?
             nil

activerecord/lib/active_record/connection_adapters/postgresql/oid.rb

@@ -145,6 +145,14 @@ def type_cast(value)
           end
         end
 
+        class Json < Type
+          def type_cast(value)
+            return if value.nil?
+
+            ConnectionAdapters::PostgreSQLColumn.string_to_json value
+          end
+        end
+
         class TypeMap
           def initialize
             @mapping = {}
@@ -244,6 +252,7 @@ def self.registered_type?(name)
         register_type 'polygon', OID::Identity.new
         register_type 'circle', OID::Identity.new
         register_type 'hstore', OID::Hstore.new
+        register_type 'json', OID::Json.new
 
         register_type 'cidr', OID::Cidr.new
         alias_type 'inet', 'cidr'

activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb

@@ -22,6 +22,7 @@ def quote(value, column = nil) #:nodoc:
           when Hash
             case column.sql_type
             when 'hstore' then super(PostgreSQLColumn.hstore_to_string(value), column)
+            when 'json' then super(PostgreSQLColumn.json_to_string(value), column)
             else super
             end
           when IPAddr
@@ -66,8 +67,11 @@ def type_cast(value, column)
             return super unless 'bytea' == column.sql_type
             { :value => value, :format => 1 }
           when Hash
-            return super unless 'hstore' == column.sql_type
-            PostgreSQLColumn.hstore_to_string(value)
+            case column.sql_type
+            when 'hstore' then PostgreSQLColumn.hstore_to_string(value)
+            when 'json' then PostgreSQLColumn.json_to_string(value)
+            else super
+            end
           when IPAddr
             return super unless ['inet','cidr'].includes? column.sql_type
             PostgreSQLColumn.cidr_to_string(value)

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -106,6 +106,9 @@ def self.extract_value_from_default(default)
           # Hstore
           when /\A'(.*)'::hstore\z/
             $1
+          # JSON
+          when /\A'(.*)'::json\z/
+            $1
           # Object identifier types
           when /\A-?\d+\z/
             $1
@@ -201,6 +204,9 @@ def simplified_type(field_type)
           # UUID type
           when 'uuid'
             :uuid
+        # JSON type
+        when 'json'
+          :json
           # Small and big integer types
           when /^(?:small|big)int$/
             :integer
@@ -267,6 +273,10 @@ def macaddr(name, options = {})
         def uuid(name, options = {})
           column(name, 'uuid', options)
         end
+
+        def json(name, options = {})
+          column(name, 'json', options)
+        end
       end
 
       ADAPTER_NAME = 'PostgreSQL'
@@ -290,7 +300,8 @@ def uuid(name, options = {})
         inet:        { name: "inet" },
         cidr:        { name: "cidr" },
         macaddr:     { name: "macaddr" },
-        uuid:        { name: "uuid" }
+        uuid:        { name: "uuid" },
+        json:        { name: "json" }
       }
 
       include Quoting

activerecord/test/cases/adapters/postgresql/json_test.rb

@@ -0,0 +1,69 @@
+# encoding: utf-8
+
+require "cases/helper"
+require 'active_record/base'
+require 'active_record/connection_adapters/postgresql_adapter'
+
+class PostgresqlJSONTest < ActiveRecord::TestCase
+  class JsonDataType < ActiveRecord::Base
+    self.table_name = 'json_data_type'
+  end
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+    begin
+      @connection.create_table('json_data_type') do |t|
+        t.json 'payload', :default => {}
+      end
+    rescue ActiveRecord::StatementInvalid
+      return skip "do not test on PG without json"
+    end
+    @column = JsonDataType.columns.find { |c| c.name == 'payload' }
+  end
+
+  def teardown
+    @connection.execute 'drop table if exists json_data_type'
+  end
+
+  def test_column
+    assert_equal :json, @column.type
+  end
+
+  def test_type_cast_json
+    assert @column
+
+    data = "{\"a_key\":\"a_value\"}"
+    hash = @column.class.string_to_json data
+    assert_equal({'a_key' => 'a_value'}, hash)
+    assert_equal({'a_key' => 'a_value'}, @column.type_cast(data))
+
+    assert_equal({}, @column.type_cast("{}"))
+    assert_equal({'key'=>nil}, @column.type_cast('{"key": null}'))
+    assert_equal({'c'=>'}','"a"'=>'b "a b'}, @column.type_cast(%q({"c":"}", "\"a\"":"b \"a b"})))
+  end
+
+  def test_rewrite
+    @connection.execute "insert into json_data_type (payload) VALUES ('{\"k\":\"v\"}')"
+    x = JsonDataType.first
+    x.payload = { '"a\'' => 'b' }
+    assert x.save!
+  end
+
+  def test_select
+    @connection.execute "insert into json_data_type (payload) VALUES ('{\"k\":\"v\"}')"
+    x = JsonDataType.first
+    assert_equal({'k' => 'v'}, x.payload)
+  end
+
+  def test_select_multikey
+    @connection.execute %q|insert into json_data_type (payload) VALUES ('{"k1":"v1", "k2":"v2", "k3":[1,2,3]}')|
+    x = JsonDataType.first
+    assert_equal({'k1' => 'v1', 'k2' => 'v2', 'k3' => [1,2,3]}, x.payload)
+  end
+
+  def test_null_json
+    @connection.execute %q|insert into json_data_type (payload) VALUES(null)|
+    x = JsonDataType.first
+    assert_equal(nil, x.payload)
+  end
+end

activerecord/test/cases/schema_dumper_test.rb

@@ -236,6 +236,13 @@ def test_schema_dump_includes_xml_shorthand_definition
       end
     end
 
+    def test_schema_dump_includes_json_shorthand_definition
+      output = standard_dump
+      if %r{create_table "postgresql_json_data_type"} =~ output
+        assert_match %r|t.json "json_data", :default => {}|, output
+      end
+    end
+
     def test_schema_dump_includes_inet_shorthand_definition
       output = standard_dump
       if %r{create_table "postgresql_network_address"} =~ output

activerecord/test/schema/postgresql_specific_schema.rb

@@ -1,7 +1,7 @@
 ActiveRecord::Schema.define do
 
   %w(postgresql_tsvectors postgresql_hstores postgresql_arrays postgresql_moneys postgresql_numbers postgresql_times postgresql_network_addresses postgresql_bit_strings postgresql_uuids
-      postgresql_oids postgresql_xml_data_type defaults geometrics postgresql_timestamp_with_zones postgresql_partitioned_table postgresql_partitioned_table_parent).each do |table_name|
+      postgresql_oids postgresql_xml_data_type defaults geometrics postgresql_timestamp_with_zones postgresql_partitioned_table postgresql_partitioned_table_parent postgresql_json_data_type).each do |table_name|
     execute "DROP TABLE IF EXISTS #{quote_table_name table_name}"
   end
 
@@ -82,6 +82,15 @@
 _SQL
   end
 
+  if 't' == select_value("select 'json'=ANY(select typname from pg_type)")
+  execute <<_SQL
+  CREATE TABLE postgresql_json_data_type (
+    id SERIAL PRIMARY KEY,
+    json_data json default '{}'::json
+  );
+_SQL
+  end
+
   execute <<_SQL
   CREATE TABLE postgresql_moneys (
     id SERIAL PRIMARY KEY,