Add json data type (#250)

* Added json data type

* Moved json type to sqlutil package

pkg/sqlutil/json.go

@@ -0,0 +1,58 @@
+package sqlutil
+
+import (
+	"database/sql/driver"
+	"encoding/json"
+	"fmt"
+)
+
+// JSON defined JSON data type, need to implements driver.Valuer, sql.Scanner interface
+type JSON json.RawMessage
+
+// Value return json value, implement driver.Valuer interface
+func (j JSON) Value() (driver.Value, error) {
+	if len(j) == 0 {
+		return nil, nil
+	}
+	bytes, err := json.RawMessage(j).MarshalJSON()
+	return string(bytes), err
+}
+
+// Scan scan value into Jsonb, implements sql.Scanner interface
+func (j *JSON) Scan(value interface{}) error {
+	if value == nil {
+		*j = JSON("null")
+		return nil
+	}
+	var bytes []byte
+	switch v := value.(type) {
+	case []byte:
+		bytes = v
+	case string:
+		bytes = []byte(v)
+	default:
+		return fmt.Errorf("Failed to unmarshal JSONB value: %+v", value)
+	}
+
+	result := json.RawMessage{}
+	err := json.Unmarshal(bytes, &result)
+	*j = JSON(result)
+	return err
+}
+
+// MarshalJSON to output non base64 encoded []byte
+func (j JSON) MarshalJSON() ([]byte, error) {
+	return json.RawMessage(j).MarshalJSON()
+}
+
+// UnmarshalJSON to deserialize []byte
+func (j *JSON) UnmarshalJSON(b []byte) error {
+	result := json.RawMessage{}
+	err := result.UnmarshalJSON(b)
+	*j = JSON(result)
+	return err
+}
+
+func (j JSON) String() string {
+	return string(j)
+}