NAME
    SQL::Schema::Versioned - Routine and convention to create/update your
    application's DB schema

VERSION
    This document describes version 0.237 of SQL::Schema::Versioned (from
    Perl distribution SQL-Schema-Versioned), released on 2019-01-13.

DESCRIPTION
    To use this module, you typically run the "create_or_update_db_schema"()
    routine at the start of your program/script, e.g.:

     use DBI;
     use SQL::Schema::Versioned qw(create_or_update_db_schema);
     my $spec = {...}; # the schema specification
     my $dbh = DBI->connect(...);
     my $res = create_or_update_db_schema(dbh=>$dbh, spec=>$spec);
     die "Cannot run the application: cannot create/upgrade database schema: $res->[1]"
         unless $res->[0] == 200;

    This way, your program automatically creates/updates database schema
    when run. Users need not know anything.

BEST PRACTICES
    It is recommended that after you create the second and subsequent
    version ("upgrade_to_v2", "upgrade_to_v3", and so on) you create and
    keep "install_v1" so you can test migration from v1->v2, v2->v3, and so
    on.

FUNCTIONS
  create_or_update_db_schema
    Usage:

     create_or_update_db_schema(%args) -> [status, msg, payload, meta]

    Routine and convention to create/update your application's DB schema.

    With this routine (and some convention) you can easily create and update
    database schema for your application in a simple way using pure SQL.

    *Version*: version is an integer and starts from 1. Each software
    release with schema change will bump the version number by 1. Version
    information is stored in a special table called "meta" (SELECT value
    FROM meta WHERE name='schema_version').

    You supply the SQL statements in "spec". "spec" is a hash which at least
    must contain the key "latest_v" (an integer) and "install" (a series of
    SQL statements to create the schema from nothing to the latest version).

    There should also be zero or more "upgrade_to_v$VERSION" keys, the value
    of each is a series of SQL statements to upgrade from ($VERSION-1) to
    $VERSION. So there could be "upgrade_to_v2", "upgrade_to_v3", and so on
    up the latest version. This is used to upgrade an existing database from
    earlier version to the latest.

    For testing purposes, you can also add one or more "install_v<VERSION>"
    key, where "XXX" is an integer, the lowest version number that you still
    want to support. So, for example, if "latest_v" is 5 and you still want
    to support from version 2, you can have an "install_v2" key containing a
    series of SQL statements to create the schema at version 2, and
    "upgrade_to_v3", "upgrade_to_v4", "upgrade_to_v5" keys. This way
    migrations from v2 to v3, v3 to v4, and v4 to v5 can be tested.

    You can name "install_v1" key as "upgrade_to_v1" (to upgrade from
    'nothing' a.k.a. v0 to v1), which is basically the same thing.

    This routine will check the existence of the "meta" table and the
    current schema version. If "meta" table does not exist yet, the SQL
    statements in "install" will be executed. The "meta" table will also be
    created and a row "('schema_version', 1)" is added. The
    ("schema_summary", <SUMMARY>) row will also be added if your spec
    specifies a "summary".

    If "meta" table already exists, schema version will be read from it and
    one or more series of SQL statements from "upgrade_to_v$VERSION" will be
    executed to bring the schema to the latest version.

    Aside from SQL statement, the series can also contain coderefs for more
    complex upgrade process. Each coderef will be called with $dbh as
    argument and must not die (so to signify failure, you can die from
    inside the coderef).

    Currently only tested on MySQL, Postgres, and SQLite. Postgres is
    recommended because it can do transactional DDL (a failed upgrade in the
    middle will not cause the database schema state to be inconsistent, e.g.
    in-between two versions).

   Modular schema (components)
    This routine supports so-called modular schema, where you can separate
    your database schema into several *components* (sets of tables) and then
    declare dependencies among them.

    For example, say you are writing a stock management application. You
    divide your application into several components: "quote" (component that
    deals with importing stock quotes and querying stock prices),
    "portfolio" (component that deals with computing the market value of
    your portfolio, calculating gains/losses), "trade" (component that
    connects to your broker API and perform trading by submitting buy/sell
    orders).

    The "quote" application component manages these tables: "daily_price",
    "spot_price". The "portfolio" application component manages these
    tables: "account" (list of accounts in stock brokerages), "balance"
    (list of balances), "tx" (list of transactions). The "trade" application
    component manages these tables: "order" (list of buy/sell orders).

    The "portfolio" application component requires price information to be
    able to calculate unrealized gains/losses. The "trade" component also
    needs information from the "daily_price" e.g. to calculate 52-week
    momentum, and writes to the "spot_price" to record intraday prices, and
    reads/writes from the "account" and "balance" tables. Here are the
    "spec"s for each component:

     # spec for the price application component
     {
         component_name => 'price',
         summary => "Price application component",
         latest_v => 1,
         provides => ['daily_price', 'spot_price'],
         install => [...],
         ...
     }
 
     # spec for the portfolio application component
     {
         component_name => 'portfolio',
         summary => "Portfolio application component",
         latest_v => 1,
         provides => ['account', 'balance', 'tx'],
         deps => {
             'daily_price' => 1,
             'spot_price'  => 1,
         },
         install => [...],
         ...
     }
 
     # spec for the trade application component
     {
         component_name => 'trade',
         summary => "Trade application component",
         latest_v => 1,
         provides => ['order'],
         deps => {
             'daily_price' => 1,
             'spot_price'  => 1,
             'account'     => 1,
             'balance'     => 1,
         },
         install => [...],
         ...
     }

    You'll notice that the three keys new here are the "component_name",
    "provides", and "deps".

    When "component_name" is set, then instead of the "schema_version" key
    in the "meta" table, your component will use the
    "schema_version.<COMPONENT_NAME>" key. When "component_name" is not set,
    it is assumed to be "main" and the "schema_version" key is used in the
    "meta" table. The component "summary", if specified, will also be
    written to "schema_summary.<COMPONENT_NAME>" key.

    "provides" is an array of tables to help this routine know which
    table(s) your component create and maintain. If unset, this routine will
    try to guess from looking at "CREATE TABLE" SQL statements.

    This routine will create "table.<TABLE_NAME>" keys in the "meta" table
    to record which components currently maintain which tables. The value of
    the key is "<COMPONENT_NAME>:<VERSION>". When a component no longer
    maintain a table in the newest version, the corresponding
    "table.<TABLE_NAME>" row in the "meta" will also be removed.

    "deps" is a hash. The keys are table names that your component requires.
    The values are integers, meaning the minimum version of the required
    table (= component version). In the future, more complex dependency
    relationship and version requirement will be supported.

    This function is not exported by default, but exportable.

    Arguments ('*' denotes required arguments):

    *   create_from_version => *int*

        Instead of the latest, create from this version.

        This can be useful during testing. By default, if given an empty
        database, this function will use the "install" key of the spec to
        create the schema from nothing to the latest version. However, if
        this option is given, function wil use the corresponding
        "install_v<VERSION>" key in the spec (which must exist) and then
        upgrade using the "upgrade_to_v<VERSION>" keys to upgrade to the
        latest version.

    *   dbh* => *obj*

        DBI database handle.

    *   spec* => *hash*

        Schema specification, e.g. SQL statements to create and update the
        schema.

        Example:

         {
             latest_v => 3,
 
             # will install version 3 (latest)
             install => [
                 'CREATE TABLE IF NOT EXISTS t1 (...)',
                 'CREATE TABLE IF NOT EXISTS t2 (...)',
                 'CREATE TABLE t3 (...)',
             ],
 
             upgrade_to_v2 => [
                 'ALTER TABLE t1 ADD COLUMN c5 INT NOT NULL',
                 sub {
                     # this subroutine sets the values of c5 for the whole table
                     my $dbh = shift;
                     my $sth_sel = $dbh->prepare("SELECT c1 FROM t1");
                     my $sth_upd = $dbh->prepare("UPDATE t1 SET c5=? WHERE c1=?");
                     $sth_sel->execute;
                     while (my ($c1) = $sth_sel->fetchrow_array) {
                         my $c5 = ...; # calculate c5 value for the row
                         $sth_upd->execute($c5, $c1);
                     }
                 },
                 'CREATE UNIQUE INDEX i1 ON t2(c1)',
             ],
 
             upgrade_to_v3 => [
                 'ALTER TABLE t2 DROP COLUMN c2',
                 'CREATE TABLE t3 (...)',
             ],
 
             # provided for testing, so we can test migration from v1->v2, v2->v3
             install_v1 => [
                 'CREATE TABLE IF NOT EXISTS t1 (...)',
                 'CREATE TABLE IF NOT EXISTS t2 (...)',
             ],
         }

    Returns an enveloped result (an array).

    First element (status) is an integer containing HTTP status code (200
    means OK, 4xx caller error, 5xx function error). Second element (msg) is
    a string containing error message, or 'OK' if status is 200. Third
    element (payload) is optional, the actual result. Fourth element (meta)
    is called result metadata and is optional, a hash that contains extra
    information.

    Return value: (any)

FAQ
  Why use this module instead of other similar solution?
    Mainly simplicity. I write simple application which is often
    self-contained in a single module/script. This module works with
    embedded SQL statements instead of having to put SQL in separate
    files/subdirectory.

  How do I see each SQL statement as it is being executed?
    Try using Log::ger::DBI::Query, e.g.:

     % perl -MLog::ger::DBI::Query -MLog::ger::Output=Screen -MLog::ger::Level::trace yourapp.pl ...

HOMEPAGE
    Please visit the project's homepage at
    <https://metacpan.org/release/SQL-Schema-Versioned>.

SOURCE
    Source repository is at
    <https://github.com/perlancar/perl-SQL-Schema-Versioned>.

BUGS
    Please report any bugs or feature requests on the bugtracker website
    <https://rt.cpan.org/Public/Dist/Display.html?Name=SQL-Schema-Versioned>

    When submitting a bug or request, please include a test-file or a patch
    to an existing test-file that illustrates the bug or desired feature.

SEE ALSO
    Some other database migration tools on CPAN:

    *   DBIx::Migration

        Pretty much similar to this module, with support for downgrades. OO
        style, SQL in separate files/subdirectory.

    *   Database::Migrator

        Pretty much similar. OO style, SQL in separate files/subdirectory.
        Perl scripts can also be executed for each version upgrade. Meta
        table is configurable (default recommended is 'AppliedMigrations').

    *   sqitch

        A more proper database change management tool with dependency
        resolution and VCS awareness. No numbering. Command-line script and
        Perl library provided. Looks pretty awesome and something which I
        hope to use for more complex applications.

AUTHOR
    perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2019, 2018, 2017, 2015, 2014, 2013 by
    perlancar@cpan.org.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

