DESCRIPTION

Tangram has taken a concept very familiar to programmers in Java land to its logical completion.

This document is an attempt by the coders of Tangram to summarise the major problems that are inherant in the design, describe cases for which the Tangram metaphor does not work well, and list long standing TO-DO items.

DESIGN CAVEATS

query language does not cover all SQL expressions

Whilst there is no underlying fault with the query object metaphor per se, there are currently lots of queries that cannot be expressed in current versions of Tangram, and adding new parts to the language is not easy.

some loss of encapsulation with queries

It could be said this is not a problem. After all, adding properties to a schema of an object is akin to declaring them as ``public''.

Some people banter on about data access patterns, which the Tangram schema represents. But OO terms like that are usually treated as buzzwords anyway.

HARD PROBLEMS

partial column select

This optimisation has some serious dangers associated with it.

It could either be

no support for SQL UPDATE

It may be possible to write a version of "$storage->select()" that does this, which would look something like:

  $storage->update
      ( $r_object,
        set => [ $r_object->{bar} == $r_object->{baz} + 2 ],
        filter => ($r_object->{frop} != undef)
      );

no explicit support for re-orgs

The situation where you have a large amount of schema reshaping to do, with a complex enough data structure can turn into a fairly difficult problem.

It is possible to have two Tangram stores with different schema and simply load objects from one and put them in the other - however the on-demand autoloading combined with the automatic insertion of unknown objects will result in the entire database being loaded into core if it is sufficiently interlinked.

replace SQL expression core

The whole SQL expression core needs to be replaced with a SQL abstraction module that is a little better planned. For instance, there should be placeholders used in a lot more places where the code just sticks in an integer etc.

support for `large' collections

Where it is impractical or undesirable to load all of a collection into memory, when you are adding a member and then updating the container, it should be possible to do this without loading the entire collection into memory.

This could actually be achieved with a new Tangram::Type.

MISSING FEATURES

concise query expressions

For simple selects, the query syntax is too long. Getting remote objects should take less code.

non-ID joins

We can't join on anything but ``ID'' values

tables with no primary key

We can't map tables unless they have a primary key, and it is called ``id'' (or, at least, the same name as the rest of the schema).

tables with multi-column primary keys

We can't map tables when they have multiple primary keys. Well, you can, but only if you make a view with an ID column which is functionally derived from the multi-part keys. But that sucks.

tables with auto_increment keys

These suck, but Tangram could still support them without requiring schema hacks.

tables without a `type' column

The 'type' column is unneeded for base tables which do not have sub-classes.

tables with custom `type' columns

For mapping schemata where some clever person has invented their own special way of representing types using discrete column values.

tables with implicit (presence) `type' columns

It should be possible to infer the type value based on knowledge of the schema, and the tables which have rows.

fully symmetric relationships

back-refs are read-only.

bulk inserts

Inserting lots of similar objects should be more efficient. Right now it generates a new DBI statement handler for each object.

`empty subclass' schema support

You should not need to explicitly add new classes to a schema if a superclass of them is already in the schema.

warn about column redefinitions

Defining a column twice should be an error. Reported by Mark Lawrence.