KDb/Drivers/Loopback

Design document

started: may 2005 by jstaniek
status: idea and some design, volunteers needed

The Loopback driver is a higher-level driver that performs introspection into plugged-in data sources and returns available information in a form of db views.

Example

Most important db views can look like the Schema Table of SQLite https://sqlite.org/schematab.html

CREATE TABLE sqlite_schema(
 type text,
 name text,
 tbl_name text,
 rootpage integer,
 sql text
);

Then, you can perform SELECT queries on the table.

Why?

This feature gives the overview of database objects and fields, eg. for creating a design report without a need for custom coding. As a consequence, e.g. KEXI can display data from this table as from any other tables, if this KDb driver is accessible.

We also get alternative way for schema introspection: by running a query, like:

SELECT * FROM TABLES WHERE name="foobar"

instead of using the KDb API (pseudocode):

KDbConnection::tableSchema("foobar")

How would it be used in KEXI?

A KDbConnection can be allocated but note the differences between Loopback connection and "regular" one:

the driver will not be generally available within KEXI GUI (not in connection dialog's list of drivers)
despite above, it's possible to provide a project-wide option called "Show system objects" (MSA has this option as well)
the connection is read only (at least that's the assumption for now)
the connection is tied to an opened project: there is one such connection (we can make it available within a KexiProject object in a global space.

Dependencies

Implementation of the driver depends:

Database Views in KDb (not yet available, but that's similar to table schemas)
Multiple opened connections within a single project instance (not yet available)
Optional dependency: linking native databases to a project.