[mythtv] Missed recordings caused by EIT guide update

[Klaas de Waal]

As discussed, the problem of missed single recordings is caused by the starttime
of programs being changed by the guide updates from the EIT.

I am now testing a fix that does the following.
In addition to updating the starttime in database table program (and in the
associated tables credits, programrating and programgenres) the starttime
is now also updated in table record when the program is present there.

However, there may be a better solution possible.
The underlying problem, as I understand it, is that the programs, i.e.
the records in table program, can only be identified by the fields
chanid plus starttime. This means there is no way to identify a
program when the starttime of the program can have been changed.

It is possible to give tables a separate field to be used as the
primary key, independent of the content of the rest of the record.
This is done in table record which has field recordid as primary key.
Same for table capturecard with primary key cardid.

If the table program would also have a independent primary key then it
would be possible to refer to programs (records in table program) using
that key instead of using the starttime. This then makes it possible to
have a reference to a program in which all fields including the starttime
can be changed.

The advantage of the fix currently being tested is that it does not require
a change in the database schema and that it comprises only a few lines of code.
Nevertheless, when and if there is a database schema change forthcoming it might
be a good moment to add a field programidx to table program and to all
other tables that contain references to table program so that the code
can be cleaned up.

Or maybe there is a very good reason why not to use a separate primary
key but use startttime pluls chanid instead. Performance?

Comments are very much appreciated. In the meantime I keep on testing the fix!

Cheers,
Klaas.

N.B. There is a field programid in table program but that is used
for other purposes so that fieldname cannot be used for the primary index.

N.B. The code in programdata.cpp that does the updates is used by
mythfilldatabase as well as far as I know so anything that works with the
guide updates from EIT  should work for mythfilldatabase as well.

N.B. There is no field manualid in table record so I assume the manual records
are dealt with in another place.