Schema alias issue

[pavlis]

I was revising the Metadata tutorial and ran across something that is either a gap in the implementation of Schema or something you (Ian) may have decided to omit.

In MetadataDefinitions we had this method:

  /*! \brief Apply a set of aliases to data.

  This method should be called in processing workflows to apply a series
  of defined aliases to data.  The method uses the is_alias method to
  verify if an alias name is valid.  It will not change the key if the name is
  not defined as a valid alias.   The keys that fail that test will be
  posted to the std::list that is returned.   Callers should test the
  size of the return and if it is not empty take appropriate action.

    \param d is the data to alter (usually actually a TimeSeries of Seismogram)
    \param aliaslist is a list of aliases names to apply.

    \return std::list of srings of failed changes.  Callers should
     test the size of this return and take action if needed.
    */
std::list<std::string> apply_aliases(mspass::utility::Metadata& d,
          const std::list<std::string> aliaslist);

The idea of this method was to automate the process of applying a standard set of aliases like obspy or SAC. That method is not found in schema.py. In fact, I just realized it is noted in the file as "TODO".

What is the plan for that? We might want to consider a different design than the C++ code. Seems to me a useful signature for the implementation in python would be this:

def apply_aliases(self,md,alias_name='SAC',alias_to_apply=None):

md is the Metadata container to apply the aliases to, alias_name would refer to a defined name set like SAC and alias_to_apply would be a dict (might prefer a list of 2 element tuples) of a custom set of aliases to apply. The later would provide a mechanism to define aliases on the fly without having to define the aliases in the schema. That functionality might be a problem thought. Not sure enough about what is cached in the current schema.py implementation.

[wangyinz]

I just had that implemented in 89adaf3. It uses dict as the input and will automatically reference of all the aliases in its internal container, so users can call the clear_alias method from the same schema object to reverse the change. I think that should work.

[pavlis]

Cool, useful addition.