What version of NiFi are you using? Is the "value" column in your database table a String or a Float/Double? What processor(s) are you using to read from the database? If using ExecuteSQL, could you do something like the following? SELECT metric, CAST(value AS DOUBLE) AS value, timestamp, tags from myTable Alternatively, as of NiFi 1.2.0 (HDF 3.0) you can use the JoltTransformJSON processor to do type conversion (see an example here). Also if you know what the schema is supposed to be, you could use ConvertRecord with a JsonRecordSetWriter which is associated with the "correct" schema. The reader can be an AvroReader which uses the Embedded Schema. ... View more

It appears you want to set the destination path to the value of type, followed by the value of id, followed by data.txt, and in the content of that file you want the single-element JSON array containing the object that provided the values. If that is the case: As of NiFi 1.3.0, there is a PartitionRecord processor which will do most of what you want. You can create a JsonReader using the following example schema: {"type":"record","name":"test","namespace":"nifi", "fields": [ {"name":"type","type":"string"}, {"name":"id","type":"string"}, {"name":"content","type":"string"} ] } You can also create a JsonRecordSetWriter that inherits the schema (as of NiFi 1.4.0) or uses the same one (prior to NiFi 1.4.0). Then in PartitionRecord you would create two user-defined properties, say record.type and record.id, configured as follows: Given your example data, you will get 4 flow files, each containing the data from the 4 groups you mention above. Additionally you have record.type and record.id attributes on those flow files. You can route them to UpdateAttribute where you set filename to data.txt and absolute.path to /${type}/${id}. Then you can send them to PutHDFS where you set the Directory to ${absolute.path}. ... View more