Accessing the environment tree

The environment tree is always created when the logical tree is created for an input message. However, the message flow neither populates it, nor uses its contents. You can use this tree for your own purposes, for example, to pass information from one node to another. You can use the whole tree as a scratchpad or working area.

The advantage of creating your own data in environment is that this data is propagated as part of the logical tree to subsequent nodes in the message flow. If you create a new output message in a Compute node, the environment tree is also copied from the input message to the new output message. (In contrast to the local environment tree, which is only included in the output message if you explicitly request that it is).

Only one environment tree is present for the duration of the message flow. Any data updates, or additions, that you make in one node are retained, and all of the nodes in the message flow have access to the latest copy of this tree. Even if the message flows back through the message flow (for example, if an exception is thrown, or if the message is processed through the second terminal of the FlowOrder node), the latest state is retained. (In contrast to the local environment tree, which reverts to its previous state if the message flows back through the message flow.)

SET Environment.Variables = 
      ROW('granary' AS bread, 'reisling' AS wine, 'stilton' AS cheese);
SET Environment.Variables.Colors[] = 
      LIST{'yellow', 'green', 'blue', 'red', 'black'};
SET Environment.Variables.Country[] = LIST{ROW('UK' AS name, 'pound' AS currency),
   	 ROW('USA' AS name, 'dollar' AS currency)};

This information is now available to all nodes to which a message is propagated, regardless of their relative position in the message flow.

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