Reading and Writing Data

Reading Attributes

Reading attributes is done with the read method. This method exists for both the client and the server.

Read parameters

NodeId | NodeID[]:

(NodeId) A signle identifier of a node or an array of node identifiers. it will try to read 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 (NodeId) The identifier of a node

AttributeId (uint32) Node 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

local ObjectsFolder = "i=85"
local TypesFolder = "i=86"

-- Read all possible attributes of the any node
-- For part of attributes will be returned a valus
-- and for part of attributes will be returned a status code BadAttributeIdInvalid
resp,err = client:read(ObjectsFolder)
for i,result in ipairs(resp.Results) do
  if result.StatusCode == 0 then
    ua.Tools.printTable("result", result.Value)
  else
    trace(string.format("Read attributes error: 0x%X", result.StatusCode))
  end
end

Full source

Read Attributes Of Several Nodes

local ObjectsFolder = "i=85"
local TypesFolder = "i=86"

-- Read all possible attributes of several nodes
-- For part of attributes will be returned a valus
-- and for part of attributes will be returned a status code BadAttributeIdInvalid
resp,err = client:read({ObjectsFolder, TypesFolder})
for i,result in ipairs(resp.Results) do
  if result.StatusCode == 0 then
    ua.Tools.printTable("result", result.Value)
  else
    trace(string.format("Read value error: 0x%X", result.StatusCode))
  end
end

Full source

Read Variables Values

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

local Server_ServerStatus_BuildInfo_SoftwareVersion = "i=2260"

local readParams = {
  NodesToRead = {
    {
      NodeId = Server_ServerStatus_CurrentTime,
      AttributeId = ua.Types.AttributeId.Value
    },
    {
      NodeId = Server_ServerStatus_BuildInfo_SoftwareVersion,
      AttributeId = ua.Types.AttributeId.Value
    },
  }
}

resp,err = client:read(readParams)
for i,result in ipairs(resp.Results) do
  if result.StatusCode == 0 then
    ua.Tools.printTable("result", result.Value)
  else
    trace(string.format("Read value '%s' error: 0x%X", nodes.NodesToRead[i].NodeId, result.StatusCode))
  end
end

Full source

Writing Attributes

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

Write Parameters

NodesToWrite		Array of nodes and attributes to write
	NodeId	NodeId	The identifier of a node
	AttributeId	uint32	Node Attribute
	Value	DataValue	New value of the attribute

Write example

local Server_ServerStatus_StartTime = "i=2257"

local nodes = {
    NodesToWrite = {
      {
        NodeId = ua.NodeIds.Server_ServerStatus_StartTime,
        AttributeId = AttributeId.Value,
        Value = {   -- DataValue
          Value = { -- Variant
            DateTime = 0.0
          }
        }
      }
    }
  }

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

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

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