I was reading madermans post about Composing a SQL statement and I was reminded of some very peculiar software architecture I saw last year. As I started writing this I realised I had gone way offtopic, but I still wanted the monastary's opinion.

This system I was working on had introduced 'SQL abstraction layer' between the database functions layer and the database itself:

webserver
CGI layer
processing
DB functions layer
SQL abstraction layer
DBI/DBD
database

The DB functions layer defined commonly used functions like 'add_user' 'add_transaction'. Such layers are common, and they allow you to cleanly change the database backend without worrying about the front. But in this case the DB functions layer didn't directly use SQL... Instead it called from an array of new functions derived from the level below, eg:

&my_db_connection->update(
    table_name  => $table_name,
    keys        => &my_db_connection->select(
        table_name   => $table_name,
        return_field => 'userID',
        select_field => 'userName',
        value        => $username),
    update_field => 'userAddress',
    update_value => $new_address);
[download]

The select and update methods would generate and execute the SQL. I was expecting to find a more direct generation of SQL, eg:

 $sql = "UPDATE users SET userAddress='$new_address' WHERE userName='$
+username'"
[download]

The only advantages of this approach (IMHO) are:

• Security - malicious code has to navigate an extra layer of obscurity
• Safe development - Once the abstraction layer is written, developers working on higher levels are limited in the damage they can do (can't "DROP TABLE")

Whereas the disadvantages are:

• New set of functions - Developers had to learn these new functions, their SQL knowledge was useless.
• Extra complexity - extra bugs
• Less Efficient
• Less Flexibility
• Database locked to code - (yes, major rewrites were required if you added a DB column)

And of course all of the other issues that arise simply by virtue of writing an extra 2000 lines of code

Has anyone got ANY ideas why the original developers might have done this ? ? ?

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