.. _read_write_data:

========================
Reading and Writing Data
========================


.. _read_attributes:

Reading Attributes
##################

Reading attributes is done with the *read* method. This method
exists for both the :ref:`client <client:read>` and the :ref:`server <server:read>`.

Read parameters
---------------

:NodeId | NodeID[]: (:ref:`NodeId<node_id_type>`)
  A signle identifier of a node or an array of node identifiers.
  it will try to read :ref:`all attributes <all_attributes>` of a node.
  For existing attributes will be returned value,
  for absent attrubutes of a noe will be returned status code BadAttributeIdInvalid.

:NodesToRead[]: An array of tables with the following fields:

  **NodeID** (:ref:`NodeId<node_id_type>`) The identifier of a node

  **AttributeId** (uint32) :ref:`attribute` Attribute of node to read

  With these parameters you can read exact attributes of a node, for example, the value of a variable.
  values of several variable nodes.

Read Attributes Of One Node
---------------------------

.. literalinclude:: examples/client/client_read.lua
    :language: lua
    :lines: 44-57

`Full source <_static/client/client_read.lua>`__

Read Attributes Of Several Nodes
--------------------------------

.. literalinclude:: examples/client/client_read.lua
    :language: lua
    :lines: 44-46, 59-69

`Full source <_static/client/client_read.lua>`__

Read Variables Values
---------------------

Variables in the OPCUA holds valuable data in the attribute Value.
It is possible to read several values at once.

.. literalinclude:: examples/client/client_read.lua
    :language: lua
    :lines: 73-96

`Full source <_static/client/client_read.lua>`__

Writing Attributes
##################

Changing the values of attributes is done with the Write method.

Write Parameters
----------------

+----------------------------------+---------------------------------------------------------------+
| **NodesToWrite**                 | Array of nodes and attributes to write                        |
+----------------+-----------------+-----------------------------------+---------------------------+
|                | **NodeId**      | :ref:`NodeId<node_id_type>`       | The identifier of a node  |
|                +-----------------+-----------------------------------+---------------------------+
|                | **AttributeId** | uint32                            | :ref:`attribute`          |
|                +-----------------+-----------------------------------+---------------------------+
|                | **Value**       | :ref:`DataValue<data_value_type>` | New value of the attribute|
+----------------+-----------------+-----------------------------------+---------------------------+


Write example
-------------

.. code-block:: lua

  local Server_ServerStatus_StartTime = "i=2257"

  local nodes = {
      NodesToWrite = {
        {
          NodeId = ua.NodeIds.Server_ServerStatus_StartTime,
          AttributeId = AttributeId.Value,
          Value = {   -- DataValue
            Type = ua.VariantType.DateTime,
            Value = 0.0,
            StatusCode = ua.StatusCode.Good
          }
        }
      }
    }

  local response = svc:write(nodes)
  if response.Results[1] ~= ua.StatusCode.Good then
    print(string.format("Changing attribute value failed: 0x%X", response.Results[1]))
    return
  end


.. _attribute:

Node Attribute
##############

Every node in the address space is represented by a set of attributes.


Base node attribute numbers
---------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   1    |  NodeId                  | nodeID            |
+--------+--------------------------+-------------------+
|   2    |  NodeClass               | uint32            |
+--------+--------------------------+-------------------+
|   3    |  BrowseName              | qualifiedName     |
+--------+--------------------------+-------------------+
|   4    |  DisplayName             | localizedText     |
+--------+--------------------------+-------------------+
|   5    |  Description             | localizedText     |
+--------+--------------------------+-------------------+
|   6    |  WriteMask               | uint32            |
+--------+--------------------------+-------------------+
|   7    |  UserWriteMask           | uint32            |
+--------+--------------------------+-------------------+
|   24   |  RolePermissions         | structure (TBD)   |
+--------+--------------------------+-------------------+
|   25   |  UserRolePermissions     | structure (TBD)   |
+--------+--------------------------+-------------------+
|   26   |  AccessRestrictions      | uint16            |
+--------+--------------------------+-------------------+


Object node attribute numbers
-----------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   *    |  Base attributes         |                   |
+--------+--------------------------+-------------------+
|   12   |  EventNotifier           | byte              |
+--------+--------------------------+-------------------+


Object Type node attribute numbers
----------------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   *    |  Base attributes         |                   |
+--------+--------------------------+-------------------+
|   8    |  IsAbstract              | boolean           |
+--------+--------------------------+-------------------+


Variable node attribute numbers
-------------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   *    |  Base attributes         |                   |
+--------+--------------------------+-------------------+
| 13     |  Value                   | DataValue         |
+--------+--------------------------+-------------------+
| 14     |  DataType                | NodeID            |
+--------+--------------------------+-------------------+
| 15     |  Rank                    | int32             |
+--------+--------------------------+-------------------+
| 16     |  ArrayDimensions         | int32[]           |
+--------+--------------------------+-------------------+
| 17     |  AccessLevel             | byte              |
+--------+--------------------------+-------------------+
| 18     |  UserAccessLevel         | byte              |
+--------+--------------------------+-------------------+
| 19     |  MinimumSamplingInterval | double            |
+--------+--------------------------+-------------------+
| 20     |  Historizing             | boolean           |
+--------+--------------------------+-------------------+
| 27     |  AccessLevelEx           | uint32            |
+--------+--------------------------+-------------------+


Variable Type node attribute numbers
------------------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   *    |  Base attributes         |                   |
+--------+--------------------------+-------------------+
| 8      |  IsAbstract              | boolean           |
+--------+--------------------------+-------------------+
| 13     |  Value                   | DataValue         |
+--------+--------------------------+-------------------+
| 14     |  DataType                | NodeID            |
+--------+--------------------------+-------------------+
| 15     |  Rank                    | int32             |
+--------+--------------------------+-------------------+
| 16     |  ArrayDimensions         | int32[]           |
+--------+--------------------------+-------------------+

Reference Type node attribute numbers
-------------------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   *    |  Base attributes         |                   |
+--------+--------------------------+-------------------+
| 8      |  IsAbstract              | boolean           |
+--------+--------------------------+-------------------+
| 9      |  Symmetric               | boolean           |
+--------+--------------------------+-------------------+
| 10     |  InverseName             | localizedText     |
+--------+--------------------------+-------------------+


Data Type node attribute numbers
--------------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   *    |  Base attributes         |                   |
+--------+--------------------------+-------------------+
| 8      |  IsAbstract              | boolean           |
+--------+--------------------------+-------------------+
| 23     |  DataTypeDefinition      | nodeID            |
+--------+--------------------------+-------------------+


Method node attribute numbers
-----------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   *    |  Base attributes         |                   |
+--------+--------------------------+-------------------+
| 21     |  Executable              | boolean           |
+--------+--------------------------+-------------------+
| 22     |  UserExecutable          | boolean           |
+--------+--------------------------+-------------------+


View node attribute numbers
---------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
|   *    |  Base attributes         |                   |
+--------+--------------------------+-------------------+
| 11     |  ContainsNoLoops         | boolean           |
+--------+--------------------------+-------------------+
| 12     |  EventNotifier           | byte              |
+--------+--------------------------+-------------------+

.. _all_attributes:

List of all attribute numbers
-----------------------------

+--------+--------------------------+-------------------+
| Number |  Attribute name          | Data type         |
+--------+--------------------------+-------------------+
| 1      |  NodeId                  | nodeID            |
+--------+--------------------------+-------------------+
| 2      |  NodeClass               | uint32            |
+--------+--------------------------+-------------------+
| 3      |  BrowseName              | qualifiedName     |
+--------+--------------------------+-------------------+
| 4      |  DisplayName             | localizedText     |
+--------+--------------------------+-------------------+
| 5      |  Description             | localizedText     |
+--------+--------------------------+-------------------+
| 6      |  WriteMask               | uint32            |
+--------+--------------------------+-------------------+
| 7      |  UserWriteMask           | uint32            |
+--------+--------------------------+-------------------+
| 8      |  IsAbstract              | boolean           |
+--------+--------------------------+-------------------+
| 9      |  Symmetric               | boolean           |
+--------+--------------------------+-------------------+
| 10     |  InverseName             | localizedText     |
+--------+--------------------------+-------------------+
| 11     |  ContainsNoLoops         | boolean           |
+--------+--------------------------+-------------------+
| 12     |  EventNotifier           | byte              |
+--------+--------------------------+-------------------+
| 13     |  Value                   | DataValue         |
+--------+--------------------------+-------------------+
| 14     |  DataType                | NodeID            |
+--------+--------------------------+-------------------+
| 15     |  Rank                    | int32             |
+--------+--------------------------+-------------------+
| 16     |  ArrayDimensions         | int32[]           |
+--------+--------------------------+-------------------+
| 17     |  AccessLevel             | byte              |
+--------+--------------------------+-------------------+
| 18     |  UserAccessLevel         | byte              |
+--------+--------------------------+-------------------+
| 19     |  MinimumSamplingInterval | double            |
+--------+--------------------------+-------------------+
| 20     |  Historizing             | boolean           |
+--------+--------------------------+-------------------+
| 21     |  Executable              | boolean           |
+--------+--------------------------+-------------------+
| 22     |  UserExecutable          | boolean           |
+--------+--------------------------+-------------------+
| 23     |  DataTypeDefinition      | nodeID            |
+--------+--------------------------+-------------------+
| 24     |  RolePermissions         | structure (TBD)   |
+--------+--------------------------+-------------------+
| 25     |  UserRolePermissions     | structure (TBD)   |
+--------+--------------------------+-------------------+
| 26     |  AccessRestrictions      | uint16            |
+--------+--------------------------+-------------------+
| 27     |  AccessLevelEx           | uint32            |
+--------+--------------------------+-------------------+