.. currentmodule:: riak.datatypes

Traditionally all data stored in Riak was an opaque binary type. Then in version 1.4 came the introduction of a :ref:`counter <legacy_counters>`, the first Convergent Data Type supported in Riak. In Riak 2.0, several additional Data Types were introduced. Riak "knows" about these data types, and conflicting writes to them will converge automatically without presenting :ref:`sibling values <siblings>` to the user.

Here is the list of current Data Types:

• :py:class:`~riak.datatypes.Counter` increments or decrements integer values
• :py:class:`~riak.datatypes.Set` allows you to store multiple distinct opaque binary values against a key
• :py:class:`~riak.datatypes.Map` is a nested, recursive struct, or associative array. Think of it as a container for composing ad hoc data structures from multiple Data Types. Inside a map you may store sets, counters, flags, registers, and even other maps
• :py:class:`~riak.datatypes.Register` stores binaries accoring to last-write-wins logic within :py:class:`~riak.datatypes.Map`
• :py:class:`~riak.datatypes.Flag` is similar to a boolean and also must be within :py:class:`~riak.datatypes.Map`

All Data Types must be stored in buckets bearing a :class:`~riak.bucket.BucketType` that sets the :attr:`~riak.bucket.BucketType.datatype` property to one of "counter", "set", or "map". Note that the bucket must have the allow_mult property set to true.

These Data Types are stored just like :class:`RiakObjects <riak.riak_object.RiakObject>`, so size constraints that apply to normal Riak values apply to Riak Data Types too.

An in-depth discussion of Data Types, also known as CRDTs, can be found at Data Types.

Examples of using Data Types can be found at Using Data Types.

Riak Data Types provide a further departure from Riak's usual operation, in that the API is operation-based. Rather than fetching the data structure, reconciling conflicts, mutating the result, and writing it back, you instead tell Riak what operations to perform on the Data Type. Here are some example operations:

• increment a :class:`Counter` by 10
• add 'joe' to a :class:`Set`
• remove the :class:`Set` field called 'friends' from a :class:`Map`
• enable the prepay :class:`Flag` in a :class:`Map`

Datatypes can be fetched and created just like :class:`~riak.riak_object.RiakObject` instances, using :meth:`RiakBucket.get <riak.bucket.RiakBucket.get>` and :meth:`RiakBucket.new <riak.bucket.RiakBucket.new>`, except that the bucket must belong to a bucket-type that has a valid datatype property. If we have a bucket-type named "social-graph" that has the datatype "set", we would fetch a :class:`Set` like so:

graph = client.bucket_type('social-graph')
graph.datatype  # => 'set'
myfollowers = graph.bucket('followers').get('seancribbs')
# => a Set datatype

Once we have a datatype, we can stage operations against it and then send those operations to Riak:

myfollowers.add('javajolt')
myfollowers.discard('roach')
myfollowers.update()

While this looks in code very similar to manipulating :class:`~riak.riak_object.RiakObject` instances, only mutations are enqueued locally, not the new value.

In order for Riak Data Types to behave well, you must have an opaque context received from a read when you:

• :meth:`disable <Flag.disable>` a :class:`Flag` (set it to false)
• remove a field from a :class:`Map`
• :meth:`remove <Set.discard>` an element from a :py:class:`Set`

The basic rule is "you cannot remove something you haven't seen", and the context tells Riak what you've actually seen, similar to the :ref:`vclock` on :class:`~riak.riak_object.RiakObject`. The Python client handles opaque contexts for you transparently as long as you fetch before performing one of these actions.

.. autoclass:: Datatype

   .. autoattribute:: value
   .. autoattribute:: context
   .. autoattribute:: modified

.. automethod:: Datatype.reload

.. automethod:: Datatype.update

.. function:: Datatype.store(**params)

    This is an alias for :meth:`~riak.datatypes.Datatype.update`.

.. automethod:: Datatype.delete

.. automethod:: Datatype.clear

.. autoclass:: Counter

.. attribute:: Counter.value

   The current value of the counter.

   :rtype: int

.. automethod:: Counter.increment

.. automethod:: Counter.decrement

.. autoclass:: Set

.. attribute:: Set.value

   An immutable copy of the current value of the set.

   :rtype: frozenset

.. automethod:: Set.add

.. automethod:: Set.discard

.. autoclass:: Map

.. autoattribute:: Map.value

.. attribute:: Map.counters

   Filters keys in the map to only those of counter types. Example::

        map.counters['views'].increment()
        del map.counters['points']

.. attribute:: Map.flags

   Filters keys in the map to only those of flag types. Example::

        map.flags['confirmed'].enable()
        del map.flags['attending']

.. attribute:: Map.maps

   Filters keys in the map to only those of map types. Example::

        map.maps['emails'].registers['home'].set("user@example.com")
        del map.maps['spam']

.. attribute:: Map.registers

   Filters keys in the map to only those of register types. Example::

        map.registers['username'].set_value("riak-user")
        del map.registers['access_key']

.. attribute:: Map.sets

   Filters keys in the map to only those of set types. Example::

        map.sets['friends'].add("brett")
        del map.sets['favorites']

Two of the new Data Types may only be embedded in :py:class:`Map <riak.datatypes.Map>` objects (in addition to :py:class:`Map <riak.datatypes.Map>` itself):

.. autoclass:: Register

.. autoattribute:: Register.value

.. automethod:: Register.assign

.. autoclass:: Flag

.. attribute:: Flag.value

   The current value of the flag.

   :rtype: bool, None

.. automethod:: Flag.enable

.. automethod:: Flag.disable