/ 
Alzabo-0.79_04
River stage one • 2 direct dependents • 3 total dependents
/ Alzabo::Create::Schema

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

METHODS

Constructors

new

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.

Returns

A new Alzabo::Create::Schema object.

Throws

Alzabo::Exception::Params Alzabo::Exception::System

load_from_file

Parameters

  • name => $schema_name

Returns a schema object previously saved to disk.

Returns

The Alzabo::Create::Schema object specified by the name parameter.

Throws

Alzabo::Exception::Params

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. This means that calling the make_sql method on the object won't generate any SQL. To do this you'd have to first call $schema->set_instantiated(0) and then $schema->make_sql.

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

set_name ($name)

Change 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.

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.

Returns

The Alzabo::Create::Table object created.

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. 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.

Parameters

  • table => Alzabo::Create::Table object

  • after => Alzabo::Create::Table object (optional)

    ... or ...

  • before => Alzabo::Create::Table object (optional)

Returns

The Alzabo::Create::Table object created.

Throws

Alzabo::Exception::Params

move_table

Allows you to change the order of the tables as they are stored in the schema.

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 (which makes little sense, but it's your code, so...) 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 is assumed to 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.

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.

Parameters

This method takes any parameters that can be used when connecting to the RDBMS, including user, password, host, and port.

instantiated

Returns

The value of the schema's instantiated attribute. It is true if 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.

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.

Parameters

This method takes any parameters that can be used when connecting to the RDBMS, including user, password, host, and port.

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.

Parameters

This method takes any parameters that can be used when connecting to the RDBMS, including user, password, host, and port.

sync_backend_sql

Parameters

This method takes any parameters that can be used when connecting to the RDBMS, including user, password, host, and port.

Returns

This method returns an array containing the set of SQL statements that would be used by the sync_backend_sql method.

If there is no corresponding schema in the RDBMS backend, then this method returns the SQL necessary to create the schema from scratch.

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.

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.

Parameters

  • name => $name

Returns

A new Alzabo::Create::Schema object.

save_to_file

Saves the schema to a file on disk.

is_saved

Returns true if the schema has been saved to disk.

AUTHOR

Dave Rolsky, <autarch@urth.org>