All examples of Apex say that the first operator of the DAG should be an input operator. Can this operator appear in the middle of the DAG somewhere.
Consider a case in which I have data to be fetched from the database, based on some data that has just been processed by a previous operator, this would mean that an input operator will come in the middle of the DAG somewhere.
According to the definition of an input operator it is one which does not have any input stream. But it also does the work of fetching data if a connector is used. So will it work if I fetch data somewhere in-between a DAG ?
This is an interesting use-case. You should be able to extend an input operator (say JdbcInputOperator since you want to read from a database) and add an input port to it. This input port receives data (tuples) from another operator from your DAG and updates the "where" clause of the JdbcInputOperator so it reads the data based on that. Hope that is what you were looking for.