Set Feature Count to a Variable and later use it to conditionally terminate processing.

Question

I would like to save the feature count from a reader and later use it as a conditional check before writing the data back to the database. For example if the reader feature count is 600, I would like to make sure there are 600 features after processing and before writing the feature back to the database.

I have experimented with trying to connect StatisticsCalculators to get the count, VariableSetters /Retrievers and the Terminator, but cannot get everything to work and it seams overly complicated for something so simple. Especially since I can see the feature count on each connection line. Any input or suggestions?

virtualcitymatt · Accepted Answer

You can use a Counter followed by a Sampler to sample the last feature, this feature will hold the feature count, use this to set the variable. I guess the statistics calculator would also work.

You just need to repeat the same process before writing along with a tester to test the count against the variable.

You'll need to make sure the variable is set before any features reach the variable retriever. A FeatureHolder can help here.

Just be aware that VariableSetter/Retriever do not play well with partial runs and FeatureCaching

lance · Answer

You can use a Counter followed by a Sampler to sample the last feature, this feature will hold the feature count, use this to set the variable. I guess the statistics calculator would also work.

You just need to repeat the same process before writing along with a tester to test the count against the variable.

You'll need to make sure the variable is set before any features reach the variable retriever. A FeatureHolder can help here.

Just be aware that VariableSetter/Retriever do not play well with partial runs and FeatureCaching

so what you are proposing is something along the lines of the following:

Screenshot 2021-10-24 101114 I did find and use a FeatureCounter from the FME Hub that adds the total record count to each row. This is ran twice and two fields are added; startCount and endCount. The Tester looks at the first record and compares the two fields to confirm they are the same value. I also added a FeatureHolder to delay writing and allow for termination, if needed before writing.

Set Feature Count to a Variable and later use it to conditionally terminate processing.

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