Provided by: libalzabo-perl_0.92-6_all 
NAME
Alzabo::Create::Schema - Schema objects for schema creation
SYNOPSIS
use Alzabo::Create::Schema;
DESCRIPTION
This class represents the whole schema. It contains table objects, which in turn contain columns,
indexes, etc. It contains methods that act globally on the schema, including methods to save it to disk,
create itself in an RDBMS, create relationships between tables, etc.
Instantiation
Every schema keeps track of whether it has been instantiated or not. A schema that is instantiated is
one that exists in an RDBMS backend. This can be done explicitly by calling the schema's "create()"
method. It is also implicitly set when a schema is created as the result of reverse engineering.
The most important effect of instantiation is that once a schema is instantiated, the way it generates
SQL for itself changes. Before it is instantiated, if you ask it to generate SQL via the "make_sql()"
the method, it will generate the set of SQL statements that are needed to create the schema from scratch.
After it is instantiated, the schema will instead generate the SQL necessary to convert the version in
the RDBMS backend to match the object's current state. This can be thought of as a SQL 'diff'.
While this feature is quite useful, it can be confusing too. The most surprising aspect of this is that
if you create a schema via reverse engineering and then call the "make_sql()" method, you will not get
any SQL. This is because the schema knows that it is instantiated and it also knows that it is the same
as the version in the RDBMS, so no SQL is necessary.
You can use the "set_instantiated()" method method to change whether or not the schem thinks it is
instantiated.
INHERITS FROM
"Alzabo::Schema"
Note: all relevant documentation from the superclass has been merged into this document.
METHODS
Constructors
new
This constructor takes the following parameters:
• name => $name
This is the name of the schema, and will be the name of the database in the RDBMS.
• rdbms => $rdbms
This is a string identifying the RDBMS. The allowed values are returned from the
"Alzabo::RDBMSRules->available" method. These are values such as 'MySQL', 'PostgreSQL', etc.
It returns a new "Alzabo::Create::Schema" object.
Throws: "Alzabo::Exception::Params", "Alzabo::Exception::System"
load_from_file
This constructor takes the following parameters:
• name => $schema_name
Returns a schema object previously saved to disk, as specified by the "name" parameters.
Throws: "Alzabo::Exception::Params", "Alzabo::Exception::System"
reverse_engineer
Attempts to connect to a database and instantiate a new schema object based on information in the
specified database. The returned object will have its instantiated value set to true so that subsequent
changes will lead to SQL diffs, as opposed to SQL to create the database from scratch.
The schema object returned by this method will have its instantiated attribute set as true.
It takes the following parameters:
• name => $name
The name of the database with which to connect.
• rdbms => $rdbms
See the "new" method documentation for an explanation of this parameter.
In addition, this method takes any parameters that can be used when connecting to the RDBMS, including
"user", "password", "host", and "port".
Returns a new "Alzabo::Create::Schema" object.
Other Methods
name
Returns a string containing the name of the schema.
set_name ($name)
Changes the schema name. Since schemas are saved on disk with filenames based on the schema name, this
deletes the files for the old name. Call "save_to_file()" immediately afterwards if you want to make
sure you have a copy of the schema saved.
Throws: "Alzabo::Exception::Params", "Alzabo::Exception::RDBMSRules", "Alzabo::Exception::System"
table ($name)
Returns an "Alzabo::Create::Table" object representing the specified table.
An "Alzabo::Exception::Params" exception is throws if the schema does not contain the table.
tables (@optional_list)
If no arguments are given, this method returns a list of all "Alzabo::Create::Table" objects in the
schema, or in a scalar context the number of such tables. If one or more arguments are given, returns a
list of table objects with those names, in the same order given (or the number of such tables in a scalar
context, but this isn't terribly useful).
An "Alzabo::Exception::Params" exception is throws if the schema does not contain one or more of the
specified tables.
has_table ($name)
Returns a boolean value indicating whether the table exists in the schema.
make_table
This method makes a new table and adds it to the schema, the parameters given are passed directly to the
"Alzabo::Create::Table->new()" method. The "schema" parameter is filled in automatically.
If a "before" or "after" parameter is given then the "move_table()" method will be called to move the new
table to the appropriate position.
Returns a new "Alzabo::Create::Table" object.
Throws: "Alzabo::Exception::Params", "Alzabo::Exception::RDBMSRules"
delete_table ("Alzabo::Create::Table" object)
Removes the given table from the schema. This method will also delete all foreign keys in other tables
that point at the given table.
Throws: "Alzabo::Exception::Params"
add_table
Add a table to the schema.
This methods takes the following parameters:
• table => "Alzabo::Create::Table" object
• after => "Alzabo::Create::Table" object (optional)
... or ...
• before => "Alzabo::Create::Table" object (optional)
Returns a new "Alzabo::Create::Table" object.
Throws: "Alzabo::Exception::Params"
move_table
Allows you to change the order of the tables as they are stored in the schema.
This method takes the following parameters:
• table => "Alzabo::Create::Table" object
The table to move.
and either ...
• before => "Alzabo::Create::Table" object
Move the table before this table
... or ...
• after => "Alzabo::Create::Table" object
Move the table after this table.
Throws: "Alzabo::Exception::Params"
add_relationship
Creates a relationship between two tables. This involves creating "Alzabo::Create::ForeignKey" objects
in both tables. If the "columns_from" and "columns_to" parameters are not specified then the schema
object attempts to calculate the proper values for these attributes.
To do this, Alzabo attempts to determine the dependencies of the tables. If you have specified a
cardinality of 1..1, or n..1, in cases where both tables are independent, or where they are both
dependent then the "table_from" is treated as being the dependent table for the purposes of determining
If no columns with the same names exist in the other table, then columns with those names will be
created. Otherwise, "add_relationship()" changes the dependent columns so that their
"Alzabo::Create::ColumnDefinition" objects are the same as the columns in the table upon which they are
dependent, meaning that changes to the type of one column affects both at the same time.
If you want to make a multi-column relationship, the assumption is that the order of the columns is
significant. In other words, the first column in the "columns_from" parameter should correspond to the
first column in hte "columns_to" parameter and so on.
The number of columns given in "columns_from" and "columns_to" must be the same except when creating a
many to many relationship.
If the cardinality is many to many then a new table will be created to link the two tables together.
This table will contain the primary keys of both the tables passed into this function. It will contain
foreign keys to both of these tables as well, and these tables will be linked to this new table.
This method takes the following parameters:
• table_from => "Alzabo::Create::Table" object (optional if columns_from is provided)
• table_to => "Alzabo::Create::Table" object (optional if columns_to is provided)
• columns_from => "Alzabo::Create::Column" object (optional if table_from is provided)
• columns_to => "Alzabo::Create::Column" object (optional if table_to is provided)
• cardinality => [1, 1], [1, 'n'], ['n', 1], or ['n', 'n']
• name => $name
If provided, and if the specified cardinality requires the creation of a linking table, this string
will be used to name that linking table. Otherwise, the new table's name will be synthesized from the
names of those it's linking.
• from_is_dependent => $boolean
• to_is_dependent => $boolean
• comment => $comment
Throws: "Alzabo::Exception::Params"
create
This method causes the schema to connect to the RDBMS, create a new database if necessary, and then
execute whatever SQL is necessary to make that database match the current state of the schema object. If
the schema has been instantiated previously, then it will generate the SQL necessary to change the
database. This may be destructive (dropping tables, columns, etc) so be careful. This will cause the
schema to be marked as instantiated.
Wherever possible, existing data will be preserved.
This method takes any parameters that can be used when connecting to the RDBMS, including "schema_name",
"user", "password", "host", and "port".
If a "schema_name" parameter is given, then this will be the name given to the schema in the RDBMS.
Warning: Every time you call "create()" or "sync_backend()", the schema will consider itself to have been
instantiated. This will affect how schema diffs are generated. After this, you will almost certainly
need to use "sync_backend()" to sync the RDBMS schema, since the schema's internal notion of it's state
may be incorrect.
instantiated
Returns a boolean value indicating whether the schema has been created in an RDBMS backend, otherwise it
is false.
set_instantiated ($bool)
Set the schema's instantiated attribute as true or false.
Throws: "Alzabo::Exception::Params"
make_sql
Returns an array containing the SQL statements necessary to either create the database from scratch or
update the database to match the schema object. See the "create()" method for more details.
drop
Drops the database/schema from the RDBMS. This will cause the schema to be marked as not instantiated.
This method does not delete the Alzabo files from disk. To do this, call the "delete()" method.
This method takes any parameters that can be used when connecting to the RDBMS, including "schema_name",
"user", "password", "host", and "port".
Throws: "Alzabo::Exception::Driver"
sync_backend
This method will look at the schema as it exists in the RDBMS backend, and make any changes that are
necessary in order to make this backend schema match the Alzabo schema object. If there is no
corresponding schema in the RDBMS backend, then this method is equivalent to the "create()" method.
After this method is called, the schema will be considered to be instantiated.
This method will never be perfect because some RDBMS backends alter table definitions as they are
created. For example, MySQL has default column "lengths" for all of its integer columns. Alzabo tries
to account for these.
In the end, this means that Alzabo may never think that a schema in the RDBMS exactly matches the state
of the Alzabo schema object. Even immediately after running this method, running it again may still
cause it to execute SQL commands. Fortunately, the SQL it generates will not cause anything to break.
This method takes any parameters that can be used when connecting to the RDBMS, including "schema_name",
"user", "password", "host", and "port".
Throws: "Alzabo::Exception::Driver"
sync_backend_sql
If there is no corresponding schema in the RDBMS backend, then this method returns the SQL necessary to
create the schema from scratch.
This method takes any parameters that can be used when connecting to the RDBMS, including "schema_name",
"user", "password", "host", and "port".
Throws: "Alzabo::Exception::Driver"
delete
Removes the schema object from disk. It does not delete the database from the RDBMS. To do this you
must call the "drop" method first.
Throws: "Alzabo::Exception::System"
clone
This method creates a new object identical to the one that the method was called on, except that this new
schema has a different name, it does not yet exist on disk, its instantiation attribute is set to false.
It takes the following parameters:
• name => $name
This method returns a new Alzabo::Create::Schema object.
Throws: "Alzabo::Exception::Params", "Alzabo::Exception::RDBMSRules"
save_to_file
Saves the schema to a file on disk.
Throws: "Alzabo::Exception::System"
runtime_clone
Returns a new "Alzabo::Runtime::Schema" object based on the current schema.
is_saved
Returns true if the schema has been saved to disk.
begin_work
Starts a transaction. Calls to this function may be nested and it will be handled properly.
rollback
Rollback a transaction.
commit
Finishes a transaction with a commit. If you make multiple calls to "begin_work()", make sure to call
this method the same number of times.
run_in_transaction ( sub { code... } )
This method takes a subroutine reference and wraps it in a transaction.
It will preserve the context of the caller and returns whatever the wrapped code would have returned.
driver
Returns the "Alzabo::Driver" object for the schema.
rules
Returns the "Alzabo::RDBMSRules" object for the schema.
sqlmaker
Returns the "Alzabo::SQLMaker" object for the schema.
AUTHOR
Dave Rolsky, <autarch@urth.org>
perl v5.34.0 2022-06-14 Alzabo::Create::Schema(3pm)