Re: dblink_ora - a first shot on Oracle ...

Hans-Jürgen Schönig wrote:
> Thanks a lot. I will integrate named connections as proposed by the most 
> recent version of dblink as soon as possible.
> Thanks for doing the configure stuff. What we need is Oracle's OCI 
> interface and libsqlora (http://www.poitschke.de/libsqlora8/).

I was thinking that we should be merging dblink_ora (and eventually 
jdbclink) into dblink. If you wanted to start down that road, here are 
my thoughts on how that should be done.

dblink functions can be roughly divided into three groups. I'll address 
each one separately:

1) connection related

    SQL interface:
    --------------
    1.a dblink_connect (text <conn_str>)
    1.b dblink_connect (text <conn_name>, text <conn_str>)
    1.c dblink_disconnect ()
    1.d dblink_disconnect (text <conn_name>)

    To these I would add:
    1.e  dblink_connect (text <name>, text <conn_str>, text <conn_type>)

    Acceptable values for <conn_type> would be 'postgres', 'oracle', and
    eventually 'jdbc', non-case-sensitive. New types could be added to
    this list later if/when other connection types are developed.

    1.a and 1.b would default to type 'postgres'. Hence the only way to
    get a non-postgres connection would be to use a named persistent
    connection, but I think that makes sense anyway.

    Implementation:
    ---------------
    There are actually only two underlying functions, dblink_connect()
    and dblink_disconnect(). Both of these should be modified so that
    the mode (i.e. unnamed_default, named_default, named_with_type) is
    discovered based on the arguments, then the real work farmed out to
    connection type specific functions. I'm not entirely sure how it
    should be handled when, for instance, the oracle library is not found
    by configure. I suppose in that case you can use #ifdef's to provide
    stubs with appropriate error messages.

2) connection consumers

    SQL interface:
    --------------
    2.a dblink_open (text <cursor_name>, text <sql>)
    2.b dblink_fetch (text <cursor_name>, int <num>)
    2.c dblink_close (text <cursor_name>)
    2.d dblink (text <sql>)
    2.e dblink_exec (text <sql>)
    2.f dblink_open (text <conn_name>, text <cursor_name>, text <sql>)
    2.g dblink_fetch (text <conn_name>, text <cursor_name>, int <num>)
    2.h dblink_close (text <conn_name>, text <cursor_name>)
    2.i dblink (text <conn_name_or_str>, text <sql>)
    2.j dblink_exec (text <conn_name_or_str>, text <sql>)

    2.a - 2.e all use the unnamed connection and therefore only apply
    to connections of type 'postgres'

    2.f - 2.h all use named connections

    2.i and 2.j can use named connections or connection strings

    The existing named connections functions can be made to work with
    <conn_type> == 'oracle', etc. It probably makes sense to add two
    functions:
    2.k dblink (text <conn_str>, text <conn_type>, text <sql>)
    2.l dblink_exec (text <conn_str>, text <conn_type>, text <sql>)
    This would allow dynamic specification of connections to
    connection types other than 'postgres'.

    Implementation:
    ---------------
    Similar to the above, there is only one underlying function for each
    SQL function name. These should be modified in a similar manner as
    the connection functions.

3) miscellaneous utility functions

    SQL interface:
    --------------
    3.a dblink_get_pkey
    3.b dblink_build_sql_insert
    3.c dblink_build_sql_delete
    3.d dblink_build_sql_update
    3.e dblink_current_query

    These functions don't use libpq, they use SPI or other internals.
    I wouldn't try to support other types of databases for them.


> Joe, you have told me some time ago that you are planning some sort of 
> connection table which tells dblink to establish some connections 
> automatically. Did you work on that?
No, I wouldn't worry too much about that right now.

Comments?

Joe