Oj uses modes to switch the load and dump behavior. Initially Oj supported on the :object mode which uses a format that allows Ruby object encoding and decoding in a manner that lets almost any Ruby object be encoded and decoded without monkey patching the object classes. From that start other demands were made the were best met by giving Oj multiple modes of operation. The current modes are:
Since modes determine what the JSON output will look like and alternatively what Oj expects when the
Oj.load() method is called, mixing the output and input mode formats will most likely not behave as intended. If the object mode is used for producing JSON then use object mode for reading. The same is true for each mode. It is possible to mix but only for advanced users.
Strict mode follows the JSON specifications and only supports the JSON native types, Boolean, nil, String, Hash, Array, and Numbers are encoded as expected. Encountering any other type causes an Exception to be raised. This is the safest mode as it is just simple translation, no code outside Oj or the core Ruby is execution on loading. Very few options are supported by this mode other than formatting options.
Null mode is similar to the :strict mode except that a JSON null is inserted if a non-native type is encountered instead of raising an Exception.
:compat or :json Mode
:compat mode mimics the json gem. The json gem is built around the use of the
to_json(*) method defined for a class. Oj attempts to provide the same functionality by being a drop in replacement with a few exceptions. JsonGem includes more details on compatibility and use.
:rails mode mimics the ActiveSupport version 5 encoder. Rails and ActiveSupport are built around the use of the
as_json(*) method defined for a class. Oj attempts to provide the same functionality by being a drop in replacement with a few exceptions. Rails includes more details on compatibility and use.
Object mode is for fast Ruby object serialization and deserialization. That was the primary purpose of Oj when it was first developed. As such it is the default mode unless changed in the Oj default options. In :object mode Oj generates JSON that follows conventions which allow Class and other information such as Object IDs for circular reference detection to be encoded in a JSON document. The formatting follows the rules describe on the Encoding page.
Custom mode honors all options. It provides the most flexibility although it can not be configured to be exactly like any of the other modes. Each mode has some special aspect that makes it unique. For example, the
:object mode has it's own unique format for object dumping and loading. The
:compat mode mimic the json gem including methods called for encoding and inconsistencies between
JSON(). More details on the Custom page.
WAB mode ignores all options except the indent option. Performance of this mode is on slightly better than the :strict and :null modes. It is included to support the WABuR project. More details on the WAB page.
Not all options are available in all modes. The options matrix identifies the options available in each mode. An
x in the matrix indicates the option is supported in that mode. A number indicates the footnotes describe additional information.
:allow_blank an alias for :nilnil.
The :ascii_only options is an undocumented json gem option.
By default the bigdecimal_as decimal is not set and the default encoding for Rails is as a string. Setting the value to true will encode a BigDecimal as a number which breaks compatibility.
The integer indent value in the default options will be honored by since the json gem expects a String type the indent in calls to 'to_json()', 'Oj.generate()', or 'Oj.generate_fast()' expect a String and not an integer.
The max_nesting option is for the json gem and rails only. It exists for compatibility. For other Oj dump modes the maximum nesting is set to over
If reference loops exist in the object being dumped then using the
:circularoption is a far better choice. It adds a slight overhead but detects an object that appears more than once in a dump and does not dump that object a second time.
The quirks mode option is no longer supported in the most recent json gem. It is supported by Oj for backward compatibility with older json gem versions.