The mem node

Flow wide value storage. mem values are available to any other node (in lambda expressions) within a flow.

There are 3 types of memories:

• 'single' holds a single value
• 'list' holds a list of values, value order is preserved within the list
• 'set' holds a list of values, where values have no duplicates

Here value can be any valid datatype that is supported in faxe, from a single scalar to a nested map and/or list.

The values will be held in a non persistent ets term storage.

Example 1

|mem()
.type('set')
.field('topic')
.key('topics_seen')

Holds a set of values from the field named topic. The set of values is available in lambda expression (within the same flow) with the key topics_seen.

The above set can be used in lambda expressions with the functions: ls_mem, ls_mem_list, ls_mem_set.

|where(
    lambda: member("topic", ls_mem_set('topics_seen')) 
)

This will filter out all points that have a topic field, which has already been stored in the mem set. Thus the where node will only output points with a unique topic value.

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Example 2

def default_map = 
    '{"key1":"topic/1/new", "key2":"topic/2/new", "key3":"topic/3/new"}'

|mem() 
.key('topic_lookup')
.default(default_map)
.default_json()

In the above example the mem node has no field parameter, but it is prepopulated with a json structure. The mem node is used as a lookup table here. The default value will stay in the storage as long as the node is running. With no field parameter given, a data_item coming in to the node will not overwrite the stored value.

The internal representation of the given json object is a map in faxe.

The stored map could then be use in a lambda expression:

|eval(lambda: map_get("some_field_name", ls_mem('topic_lookup'))).as('topic')

So based on the value of the field "some_field_name", the field topic will get the value of the corresponding map-key stored in the mem node.

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For a list of lambda_library functions see lambda_functions.

Parameters

Parameter	Description	Default
field( string )	field-path	undefined
key( string )	name of the value storage
type( string )	Type of mem storage, one of 'single', 'list' or 'set'	'single'
default( string | number )	Prefill the storage with this value	undefined
default_json( is_set)	When set, the default value will be interpreted as a json string	false (not set)

At least one of the parameters field and/or default has to be defined, otherwise this node will not be able to do anything useful.