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    Fey - Better SQL Generation Through Perl

      use Fey::Literal::Function;
      use Fey::Placeholder;
      use Fey::Schema;
      use Fey::SQL;

      my $schema = hand_waving();

      my $user  = $schema->table('User');
      my $group = $schema->table('Group')

      my $select = Fey::SQL->new_select();

      my $func = Fey::Literal::Function->new( 'LCASE', $user->column('username') );

      $select->select( $user->columns( 'user_id', 'username' ) )
             ->from( $user, $group )
             ->where( $group->group_id, 'IN', 1, 2, 3 )
             ->and  ( $func, 'LIKE', 'smith%' );

      print $select->sql($dbh);

    The `Fey' distribution contains a set of modules for representing the
    components of a DBMS schema, and for dynamically generating SQL queries
    based on that schema.

    Loading this module does nothing. It's just here to provide docs and a
    version number for the distro.

    You'll want to take a look at Fey::Schema, Fey::Table, and other modules
    in the distro for more details.

    The goal of the core `Fey' distro is to provide a simple, flexible way
    of *dynamically* generating complex SQL queries in Perl. Other packages
    build on top of this functionality to create a complete ORM

    If you're interested in an ORM, take a look at the `Fey::ORM' distro.

    To generate SQL with Fey, you first need to create a set of objects
    representing the tables and foreign keys in your schema. The simplest
    way to do this is to use the `Fey-Loader' distro, which will connect to
    an existing schema and generate a set of objects for you.

    Alternatively, you can create these objects via Fey's API. You would
    first create a Fey::Schema object. This object will hold all of your
    tables and foreign keys. If you want to create your schema this way, you
    should start with the Fey::Schema, Fey::Table, and Fey::FK APIs. You'll
    also want to use the Fey::Column API.

    Once you have a schema, you can generate SQL using Fey::SQL, or a
    DBMS-specific subclass of Fey::SQL.

    The emphasis in the core Fey distro is on dynamic queries, particularly
    on the tables/columns/etc involved in the query, not just the bound

    This is *not* what I mean by a dynamic query ...

     SELECT user_id FROM User where username = ?

    While this is dynamic in the sense that the username is parameterized
    and may change on each invocation, it is still easily handled by a
    phrasebook class. If that is all you need, I suggest checking out any of
    `Class::Phrasebook::SQL', `Data::Phrasebook', or `SQL::Library' on CPAN.

    Imagine that we have a database with a User table and a Message table,
    where each message has a user who is that message's creator. We might
    want to grab all the users in the database, in which case we would do a
    simple `SELECT' against the User table ...

     SELECT * FROM User

    But maybe we want to get all the users who have created a message in the
    last week:

     SELECT User.*
       FROM User JOIN Message
            USING (user_id)
      WHERE Message.creation_date >= ?

    The resultset for our query is still the same (0+ users) but the
    constraints of the query are more complex. Now imagine another dozen or
    so permutations on how we search for users. This is what I mean by
    "dynamically" generating queries.

    You probably don't need to read this if you just wanted to know how to
    use Fey.

  Why Not Use a Phrasebook?
    Let's assume we have a simple User table with the following columns:


    Limiting ourselves to queries of equality ("username = ?", "state = ?"),
    we would still need 32 (1 + 5 + 10 + 10 + 5 + 1) entries to handle all
    the possible combinations of columns. Now imagine adding in variants
    like allowing for wildcard searches using LIKE or regexes, or more
    complex variants involving an "OR" in a subclause.

    This gets even more complicated if you start adding in joins, outer
    joins, and so on. It's plain to see that a phrasebook gets too large to
    be usable at this point. You'd probably have to write a program just to
    generate the phrasebook and keep it up to date!

  Why Not String Manipulation?
    The next idea that might come to mind is to dump the phrasebook in favor
    of string manipulation. This is simple enough at first, but quickly gets
    ugly. Handling all of the possible options correctly requires lots of
    fiddly code that has to concatenate bits of SQL in the correct order,
    taking into account where to put in commas, `WHERE' vs `AND', and so on
    and so forth. I've been there, and trust me, it's madness.

  The Solution
    The core Fey modules provide a solution to the dynamic SQL problem.
    Using Fey, you can specify queries in the form of *Perl methods and
    objects*. Fey provides a set of objects to represent the parts of a
    schema, specifically tables, columns, and foreign keys. Using these
    objects along with Fey::SQL, you can easily generate very complex

    This core distro is also intended to be the foundation for building
    higher-level tools like an ORM. See `Fey::ORM' for just such a thing.

    This module comes from my experience writing and using Alzabo. Alzabo
    does everything this module does, and a lot more. The fact that Alzabo
    does so many things has become a fairly problematic in its maintenance,
    and Alzabo was over 6 years old at the time this project was begun
    (August of 2006).

    Rather than coming up with a very smart solution that allows us to use
    80% of a DBMS's functionality, I'd rather come up with a solution that's
    dumber but supports all (or at least 99%) of the DBMS's features. It's
    easy to add smarts on top of a dumb layer, but it can be terribly hard
    to add that last 20% once you've got something really smart.

    The goals for Fey, based on my experience with Alzabo, are the

    *   Provide a simple way to generate queries dynamically. I really like
        how this works with Alzabo conceptually, but Alzabo is not as
        flexible as I'd like and it's "build a data structure" approach to
        query building can become very cumbersome.

        Rather than complex data structures, with Fey you call methods on a
        `Fey::SQL' object to build up a query. This turns out to be simpler
        to work with.

        Fey, unlike Alzabo, can be used to generate multi-row updates and
        deletes, and it supports sub-selects, unions, etc. and all that
        other good stuff.

    *   Fey supports complex query creation with less fiddliness than
        Alzabo. This means that the class to represent queries is a little
        smarter and more flexible about the order in which bits are added.

        For example, in using Alzabo I often came across cases where I
        wanted to add a table to a query's join *if it hasn't already been
        added*. With Alzabo, there's no nice clean way to do this. Simply
        adding the table to the join parameter twice will cause an error. It
        would be nice to simply be able to do this

          $select->join( $foo_table => $bar_table );

        and have it do the right thing if that join already exists (where
        the right thing is just do nothing). `Fey::SQL' does exactly that.

    *   Provide the core for an RDBMS-OO mapper similar to a combination of
        `Alzabo::Runtime::Row' and `Class::AlzaboWrapper'.

        At the same time, query generation and the ORM are decoupled. You
        can use Fey::SQL to generate queries without having to every use the
        `Fey::ORM' ORM.

    *   Be declarative like Moose. In particular, the `Fey::ORM' ORM is as
        declarative as possible, and aims to emulate Moose's declarative
        sugar style where possible.

    *   Leverage the API user's SQL knowledge. Building up queries with Fey
        looks enough like SQL that you shouldn't have to think *too* hard
        about it. This means join support is baked in at a core level, as
        are subselects and ideally anything else you can do in SQL.

  Problems with Alzabo
    Here are some of the problems I've had with Alzabo over the years which
    inspired me to create Fey ...

    *   Adding support for a new DBMS to Alzabo is a lot of work, so it only
        supports MySQL and Postgres. Alzabo tries to be really smart about
        preventing users from shooting themselves in the foot, and requires
        a lot of DBMS-specific code to achieve this.

        In retrospect, being a lot dumber and allowing for foot-shooting
        makes supporting a new DBMS much easier. People generally know how
        their DBMS works, and if they generate an invalid query or table
        name, it will throw an error.

        For example, while Fey can accommodate per-DBMS query (sub)classes,
        it does not include any by default, and is capable of supporting
        many DBMS-specific features without per-DBMS classes.

    *   Alzabo has too much DBMS-specific knowledge. If you want to use a
        SQL function in a query, you have to import a corresponding Perl
        function from the appropriate `Alzabo::SQLMaker', which limits you
        to what's already defined, or forces you to go through a cumbersome
        API to define a new SQL function for use in your Perl code.

        By contrast, Fey has simple generic support for arbitrary functions
        via the `Fey::Literal::Function' class. If you need more flexibility
        you can use the `Fey::Literal::Term' subclass to generate an
        arbitrary snippet to insert into your SQL.

        A related problem is that Alzabo doesn't support multiple versions
        of a DBMS very well. Either it doesn't work with an older version at
        all, or it doesn't support some enhanced capability of a newer
        version. It mostly supports whatever version I happened to be using
        when I wrote a specific piece of functionality.

    *   There are now free GUI design tools for specific databases that do a
        better job of supporting the database in question than Alzabo ever

    *   Alzabo separates its classes into Create (for generation of DDL) and
        Runtime (for DML) subclasses, which might have been worth the memory
        savings six years ago, but just makes for an extra hassle now.

    *   When I originally developed Alzabo, I included a feature for
        generating high-level application object classes which subclass the
        Alzabo classes and add "business logic" methods. This is what is
        provided by `Alzabo::MethodMaker'.

        Nowadays, I prefer to have my business logic classes simple use the
        Alzabo classes. In other words, I now prefer "has-a" and "uses-a"
        versus "is-a" object design for this case.

        Method auto-generation based on a specific schema can be quite
        handy, but it should be done in the domain-specific application
        classes, not as a subclass of the core functionality.

    *   Storing schemas in an Alzabo-specific format is problematic for many
        reasons. It's simpler to simply get the schema definition from an
        existing schema, or to allow users to define it in code.

    *   Alzabo's referential integrity checking code was really cool back
        when I mostly used MySQL with MYISAM tables. Now it's just a
        maintenance burden and a barrier for new features.

    *   I didn't catch the testing bug until quite a while after I'd started
        working on Alzabo. Alzabo's test suite is nasty. Fey is built with
        testability in mind, and high test coverage is part of my ongoing
        goals for the project.

    *   Alzabo does too many things, which makes it hard to explain and

    When I first started working on Fey, it was named "Q". This was a nice
    short name to type, but obviously unsuitable for releasing on CPAN. I
    wanted a nice short name that could be used in multiple distributions,
    like John Siracusa's "Rose" modules.

    I was standing in the shower one day and had the following series of
    thoughts leading to Fey. Reading this will may give you an unpleasant
    insight into my mind. You have been warned.

    * SQLy
        This module is "SQL-y", as in "related to SQL". However, this name
        is bad for a number of reasons. First, it's not clear how to
        pronounce it. It may make you think of a YACC grammar ("SQL.y").
        It's a weird combo of upper- and lower-case letters.

    * SQLy => Squall
        "SQLy" and "Squall" share a number of letters, obviously.

        Squall is a single short word, which is good. However, it's a bit
        awkward to type and has a somewhat negative meaning to me, because a
        storm can mean trouble.

    * Squall => Lionheart => Faye
        Squall Lionheart is a character in Final Fantasy VIII, which IMO is
        the best Final Fantasy game before the PS2.

        The inimitable Faye Wong sang the theme song for FF VIII. I love
        Faye Wong.

    * Faye => Fey
        And thus we arrive at "Fey". It's nice and short, easy to type, and
        easy to say.

        Some of its meanings are "otherworldly" or "magical". Attempting to
        combine SQL and OO in any way is certainly unnatural, and if done
        right, perhaps magical. Fey can also mean "appearing slightly
        crazy". This project is certainly that.

    Yes, I'm a nerd, I know.

    Dave Rolsky, <>

    Please report any bugs or feature requests to `', or
    through the web interface at I will be notified, and
    then you'll automatically be notified of progress on your bug as I make

    Copyright 2006-2009 Dave Rolsky, All Rights Reserved.

    This program is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself. The full text of the license can be
    found in the LICENSE file included with this module.