NAME

       SQL::Translator::Diff - determine differences between two schemas

DESCRIPTION

       Takes two input SQL::Translator::Schemas (or SQL files) and produces ALTER statements to
       make them the same

SNYOPSIS

       Simplest usage:

        use SQL::Translator::Diff;
        my $sql = SQL::Translator::Diff::schema_diff($source_schema, 'MySQL', $target_schema, 'MySQL', $options_hash)

       OO usage:

        use SQL::Translator::Diff;
        my $diff = SQL::Translator::Diff->new({
          output_db     => 'MySQL',
          source_schema => $source_schema,
          target_schema => $target_schema,
          %$options_hash,
        })->compute_differences->produce_diff_sql;

OPTIONS

       ignore_index_names
           Match indexes based on types and fields, ignoring name.

       ignore_constraint_names
           Match constrains based on types, fields and tables, ignoring name.

       output_db
           Which producer to use to produce the output.

       case_insensitive
           Ignore case of table, field, index and constraint names when comparing

       no_batch_alters
           Produce each alter as a distinct "ALTER TABLE" statement even if the producer supports
           the ability to do all alters for a table as one statement.

       ignore_missing_methods
           If the diff would need a method that is missing from the producer, just emit a comment
           showing the method is missing, rather than dieing with an error

       producer_args
           Hash of extra arguments passed to "new" in SQL::Translator and the below "PRODUCER
           FUNCTIONS".

PRODUCER FUNCTIONS

       The following producer functions should be implemented for completeness. If any of them
       are needed for a given diff, but not found, an error will be thrown.

       •   "alter_create_constraint($con, $args)"

       •   "alter_drop_constraint($con, $args)"

       •   "alter_create_index($idx, $args)"

       •   "alter_drop_index($idx, $args)"

       •   "add_field($fld, $args)"

       •   "alter_field($old_fld, $new_fld, $args)"

       •   "rename_field($old_fld, $new_fld, $args)"

       •   "drop_field($fld, $args)"

       •   "alter_table($table, $args)"

       •   "drop_table($table, $args)"

       •   "rename_table($old_table, $new_table, $args)" (optional)

       •   "batch_alter_table($table, $hash, $args)" (optional)

           If the producer supports "batch_alter_table", it will be called with the table to
           alter and a hash, the keys of which will be the method names listed above; values will
           be arrays of fields or constraints to operate on. In the case of the field functions
           that take two arguments this will appear as an array reference.

           I.e. the hash might look something like the following:

            {
              alter_create_constraint => [ $constraint1, $constraint2 ],
              add_field   => [ $field ],
              alter_field => [ [$old_field, $new_field] ]
            }

       •   "preprocess_schema($schema)" (optional)

           "preprocess_schema" is called by the Diff code to allow the producer to normalize any
           data it needs to first. For example, the MySQL producer uses this method to ensure
           that FK constraint names are unique.

           Basicaly any changes that need to be made to produce the SQL file for the schema
           should be done here, so that a diff between a parsed SQL file and (say) a parsed
           DBIx::Class::Schema object will be sane.

           (As an aside, DBIx::Class, for instance, uses the presence of a "preprocess_schema"
           function on the producer to know that it can diff between the previous SQL file and
           its own internal representation. Without this method on th producer it will diff the
           two SQL files which is slower, but known to work better on old-style producers.)

AUTHOR

       Original Author(s) unknown.

       Refactor/re-write and more comprehensive tests by Ash Berlin "ash@cpan.org".

       Redevelopment sponsored by Takkle Inc.