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.