make error_value global to metric and add error_expression #157
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Readme.md
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| error_value: 1 | ||
| # When specified, if the value cannot be parsed or expression fails, runs this expression as fallback | ||
| # if it fails, error_value will be returned | ||
| error_expression: "float(join(filter(split(a, ''), { # matches '^[0-9]$' }), ''))" |
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I wonder why we need an error_expression? Can't we just use a normal expression to implement parsing of strings like H20241227104456? The only reason I understand are message producers writing messages in inconsistent formats so that we have to apply two different parsing strategies. Is that the case?
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using expression is not possible because it runs after type conversion and it fails as it's not a bool, a float nor a static map string
I can see several options:
- make expression to run before type conversion. but this would break all current expression implementation because the
valuesent is the value after type conversion - create another expression that runs before type conversion. Like
expression_rawand if set, return a float from whatever value is read from MQTT bypassing the current type conversion/expression - add error_expression which is kind of the same of the previous one but seems more generic.
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I actually would like to prever the second solution:
create another expression that runs before type conversion. Like expression_raw and if set, return a float from whatever value is read from MQTT bypassing the current type conversion/expression
This is more logical having a parsing expression yourself instead of doing it after the fact. In that case, if the expression returns a string, we could enable the user to parse the string first, and then apply the mapping the user specified.
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agree,
i'll push another PR with raw_expression and only keep error_value in this one
* fail if both metric.error_value and metric.string_value_mapping.error_value are set * mark metric.string_value_mapping.error_value as deprecated
in order to better handle errors in config metric:
string_mapping_value.error_valueto upper levelstring_mapping_value.error_valueas deprecatedif there's an error during type conversion or during execution of
expressionthenerror_valueis returned (if set, otherwise an error is thrown and no metric is sent)