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# Bugzilla::DB::Schema

- NAME
- SYNOPSIS
- DESCRIPTION
- NEW TO SCHEMA.PM?
- CONSTANTS
  - Referential Integrity
- METHODS
- SERIALIZATION/DESERIALIZATION
- CLASS METHODS
- ABSTRACT DATA TYPES
- SEE ALSO

# NAME

Bugzilla::DB::Schema - Abstract database schema for Bugzilla

# SYNOPSIS

      # Obtain MySQL database schema.
      # Do not do this. Use Bugzilla::DB instead.
      use Bugzilla::DB::Schema;
      my $mysql_schema = new Bugzilla::DB::Schema('Mysql');

      # Recommended way to obtain database schema.
      use Bugzilla::DB;
      my $dbh = Bugzilla->dbh;
      my $schema = $dbh->_bz_schema();

      # Get the list of tables in the Bugzilla database.
      my @tables = $schema->get_table_list();

      # Get the SQL statements need to create the bugs table.
      my @statements = $schema->get_table_ddl('bugs');

      # Get the database-specific SQL data type used to implement
      # the abstract data type INT1.
      my $db_specific_type = $schema->sql_type('INT1');

# DESCRIPTION

This module implements an object-oriented, abstract database schema. It should be considered package-private to the Bugzilla::DB module. That means that CGI scripts should never call any function in this module directly, but should instead rely on methods provided by Bugzilla::DB.

# NEW TO SCHEMA.PM?

If this is your first time looking at Schema.pm, especially if you are making changes to the database, please take a look at http://www.bugzilla.org/docs/developer.html#sql-schema to learn more about how this integrates into the rest of Bugzilla.

# CONSTANTS

`SCHEMA_VERSION`

  The 'version' of the internal schema structure. This version number is incremented every time the the fundamental structure of Schema internals changes.

  This is NOT changed every time a table or a column is added. This number is incremented only if the internal structures of this Schema would be incompatible with the internal structures of a previous Schema version.

  In general, unless you are messing around with serialization and deserialization of the schema, you don't need to worry about this constant.

`ABSTRACT_SCHEMA`

  The abstract database schema structure consists of a hash reference in which each key is the name of a table in the Bugzilla database.

  The value for each key is a hash reference containing the keys `FIELDS` and `INDEXES` which in turn point to array references containing information on the table's fields and indexes.

  A field hash reference should must contain the key `TYPE`. Optional field keys include `PRIMARYKEY`, `NOTNULL`, and `DEFAULT`.

  The `INDEXES` array reference contains index names and information regarding the index. If the index name points to an array reference, then the index is a regular index and the array contains the indexed columns. If the index name points to a hash reference, then the hash must contain the key `FIELDS`. It may also contain the key `TYPE`, which can be used to specify the type of index such as UNIQUE or FULLTEXT.

## Referential Integrity

Bugzilla::DB::Schema supports "foreign keys", a way of saying that "Column X may only contain values from Column Y in Table Z". For example, in Bugzilla, bugs.resolution should only contain values from the resolution.values field.

It does this by adding an additional item to a column, called `REFERENCES`. This is a hash with the following members:

`TABLE`

  The table the foreign key points at

`COLUMN`

  The column pointed at in that table.

`DELETE`

  What to do if the row in the parent table is deleted. Choices are `RESTRICT`, `CASCADE`, or `SET NULL`.

  `RESTRICT` means the deletion of the row in the parent table will be forbidden by the database if there is a row in this table that still refers to it. This is the default, if you don't specify `DELETE`.

  `CASCADE` means that this row will be deleted along with that row.

  `SET NULL` means that the column will be set to `NULL` when the parent row is deleted. Note that this is only valid if the column can actually be set to `NULL`. (That is, the column isn't `NOT NULL`.)

`UPDATE`

  What to do if the value in the parent table is updated. You can set this to `CASCADE` or `RESTRICT`, which mean the same thing as they do for "DELETE". This variable defaults to `CASCADE`, which means "also update this column in this table."

# METHODS

Note: Methods which can be implemented generically for all DBs are implemented in this module. If needed, they can be overridden with DB-specific code in a subclass. Methods which are prefixed with `_` are considered protected. Subclasses may override these methods, but other modules should not invoke these methods directly.

`new`

       Description: Public constructor method used to instantiate objects of this
                    class. However, it also can be used as a factory method to
                    instantiate database-specific subclasses when an optional
                    driver argument is supplied.
       Parameters:  $driver (optional) - Used to specify the type of database.
                    This routine C<die>s if no subclass is found for the specified
                    driver.
                    $schema (optional) - A reference to a hash. Callers external
                        to this package should never use this parameter.
       Returns:     new instance of the Schema class or a database-specific subclass

`_initialize`

       Description: Protected method that initializes an object after
                    instantiation with the abstract schema. All subclasses should
                    override this method. The typical subclass implementation
                    should first call the C<_initialize> method of the superclass,
                    then do any database-specific initialization (especially
                    define the database-specific implementation of the all
                    abstract data types), and then call the C<_adjust_schema>
                    method.
       Parameters:  $abstract_schema (optional) - A reference to a hash. If
                        provided, this hash will be used as the internal
                        representation of the abstract schema instead of our
                        default abstract schema. This is intended for internal
                        use only by deserialize_abstract.
       Returns:     the instance of the Schema class

`_adjust_schema`

       Description: Protected method that alters the abstract schema at
                    instantiation-time to be database-specific. It is a generic
                    enough routine that it can be defined here in the base class.
                    It takes the abstract schema and replaces the abstract data
                    types with database-specific data types.
       Parameters:  none
       Returns:     the instance of the Schema class

`get_type_ddl`
  Description

    Public method to convert abstract (database-generic) field specifiers to database-specific data types suitable for use in a `CREATE TABLE` or `ALTER TABLE` SQL statment. If no database-specific field type has been defined for the given field type, then it will just return the same field type.

  Parameters
    `$def` - A reference to a hash of a field containing the following keys: `TYPE` (required), `NOTNULL` (optional), `DEFAULT` (optional), `PRIMARYKEY` (optional), `REFERENCES` (optional)
  Returns

    A DDL string suitable for describing a field in a `CREATE TABLE` or `ALTER TABLE` SQL statement

`_get_fk_ddl`
  Description

    Protected method. Translates the `REFERENCES` item of a column into SQL.

  Params
    `$table` - The name of the table the reference is from.
    `$column` - The name of the column the reference is from
    `$references` - The `REFERENCES` hashref from a column.
  Returns

    SQL for to define the foreign key, or an empty string if `$references` is undefined.

`convert_type`

  Converts a TYPE from the "ABSTRACT_SCHEMA" format into the real SQL type.

`get_column($table, $column)`

       Description: Public method to get the abstract definition of a column.
       Parameters:  $table - the table name
                    $column - a column in the table
       Returns:     a hashref containing information about the column, including its
                    type (C<TYPE>), whether or not it can be null (C<NOTNULL>),
                    its default value if it has one (C<DEFAULT), etc.
                    Returns undef if the table or column does not exist.

`get_table_list`

       Description: Public method for discovering what tables should exist in the
                    Bugzilla database.

       Parameters:  none

       Returns:     An array of table names, in alphabetical order.

`get_table_columns`

       Description: Public method for discovering what columns are in a given
                    table in the Bugzilla database.
       Parameters:  $table - the table name
       Returns:     array of column names

`get_table_ddl`

       Description: Public method to generate the SQL statements needed to create
                    the a given table and its indexes in the Bugzilla database.
                    Subclasses may override or extend this method, if needed, but
                    subclasses probably should override C<_get_create_table_ddl>
                    or C<_get_create_index_ddl> instead.
       Parameters:  $table - the table name
       Returns:     an array of strings containing SQL statements

`_get_create_table_ddl`

       Description: Protected method to generate the "create table" SQL statement
                    for a given table.
       Parameters:  $table - the table name
       Returns:     a string containing the DDL statement for the specified table

`_get_create_index_ddl`

       Description: Protected method to generate a "create index" SQL statement
                    for a given table and index.
       Parameters:  $table_name - the name of the table
                    $index_name - the name of the index
                    $index_fields - a reference to an array of field names
                    $index_type (optional) - specify type of index (e.g., UNIQUE)
       Returns:     a string containing the DDL statement

`get_add_column_ddl($table, $column, \%definition, $init_value)`

       Description: Generate SQL to add a column to a table.
       Params:      $table - The table containing the column.
                    $column - The name of the column being added.
                    \%definition - The new definition for the column,
                        in standard C<ABSTRACT_SCHEMA> format.
                    $init_value - (optional) An initial value to set
                                  the column to. Should already be SQL-quoted
                                  if necessary.
       Returns:     An array of SQL statements.

`get_add_index_ddl`

       Description: Gets SQL for creating an index.
                    NOTE: Subclasses should not override this function. Instead,
                    if they need to specify a custom CREATE INDEX statement,
                    they should override C<_get_create_index_ddl>
       Params:      $table - The name of the table the index will be on.
                    $name  - The name of the new index.
                    $definition - An index definition. Either a hashref
                                  with FIELDS and TYPE or an arrayref
                                  containing a list of columns.
       Returns:     An array of SQL statements that will create the
                    requested index.

`get_alter_column_ddl($table, $column, \%definition)`

       Description: Generate SQL to alter a column in a table.
                    The column that you are altering must exist,
                    and the table that it lives in must exist.
       Params:      $table - The table containing the column.
                    $column - The name of the column being changed.
                    \%definition - The new definition for the column,
                        in standard C<ABSTRACT_SCHEMA> format.
                    $set_nulls_to - A value to set NULL values to, if
                        your new definition is NOT NULL and contains
                        no DEFAULT, and when there is a possibility
                        that the column could contain NULLs. $set_nulls_to
                        should be already SQL-quoted if necessary.
       Returns:     An array of SQL statements.

`get_drop_index_ddl($table, $name)`

       Description: Generates SQL statements to drop an index.
       Params:      $table - The table the index is on.
                    $name  - The name of the index being dropped.
       Returns:     An array of SQL statements.

`get_drop_column_ddl($table, $column)`

       Description: Generate SQL to drop a column from a table.
       Params:      $table - The table containing the column.
                    $column - The name of the column being dropped.
       Returns:     An array of SQL statements.

`get_drop_table_ddl($table)`

       Description: Generate SQL to drop a table from the database.
       Params:      $table - The name of the table to drop.
       Returns:     An array of SQL statements.

`get_rename_column_ddl($table, $old_name, $new_name)`

       Description: Generate SQL to change the name of a column in a table.
                    NOTE: ANSI SQL contains no simple way to rename a column,
                          so this function is ABSTRACT and must be implemented
                          by subclasses.
       Params:      $table - The table containing the column to be renamed.
                    $old_name - The name of the column being renamed.
                    $new_name - The name the column is changing to.
       Returns:     An array of SQL statements.

`get_rename_table_sql`
  Description

    Gets SQL to rename a table in the database.

  Params
    `$old_name` - The current name of the table.
    `$new_name` - The new name of the table.
  Returns: An array of SQL statements to rename a table.
`delete_table($name)`

       Description: Deletes a table from this Schema object.
                    Dies if you try to delete a table that doesn't exist.
       Params:      $name - The name of the table to delete.
       Returns:     nothing

`get_column_abstract($table, $column)`

       Description: A column definition from the abstract internal schema.
                    cross-database format.
       Params:      $table - The name of the table
                    $column - The name of the column that you want
       Returns:     A hash reference. For the format, see the docs for
                    C<ABSTRACT_SCHEMA>.
                    Returns undef if the column or table does not exist.

`get_indexes_on_column_abstract($table, $column)`

       Description: Gets a list of indexes that are on a given column.
       Params:      $table - The table the column is on.
                    $column - The name of the column.
       Returns:     Indexes in the standard format of an INDEX
                    entry on a table. That is, key-value pairs
                    where the key is the index name and the value
                    is the index definition.
                    If there are no indexes on that column, we return
                    undef.

`get_index_abstract($table, $index)`

       Description: Returns an index definition from the internal abstract schema.
       Params:      $table - The table the index is on.
                    $index - The name of the index.
       Returns:     A hash reference representing an index definition.
                    See the C<ABSTRACT_SCHEMA> docs for details.
                    Returns undef if the index does not exist.

`get_table_abstract($table)`

       Description: Gets the abstract definition for a table in this Schema
                    object.
       Params:      $table - The name of the table you want a definition for.
       Returns:     An abstract table definition, or undef if the table doesn't
                    exist.

`add_table($name, \%definition)`

       Description: Creates a new table in this Schema object.
                    If you do not specify a definition, we will
                    simply create an empty table.
       Params:      $name - The name for the new table.
                    \%definition (optional) - An abstract definition for
                        the new table.
       Returns:     nothing

`rename_table`

  Renames a table from `$old_name` to `$new_name` in this Schema object.

`delete_column($table, $column)`

       Description: Deletes a column from this Schema object.
       Params:      $table - Name of the table that the column is in.
                             The table must exist, or we will fail.
                    $column  - Name of the column to delete.
       Returns:     nothing

`rename_column($table, $old_name, $new_name)`

       Description: Renames a column on a table in the Schema object.
                    The column that you are renaming must exist.
       Params:      $table - The table the column is on.
                    $old_name - The current name of the column.
                    $new_name - The new name of hte column.
       Returns:     nothing

`set_column($table, $column, \%new_def)`

       Description: Changes the definition of a column in this Schema object.
                    If the column doesn't exist, it will be added.
                    The table that you specify must already exist in the Schema.
                    NOTE: This does not affect the database on the disk.
                    Use the C<Bugzilla::DB> "Schema Modification Methods"
                    if you want to do that.
       Params:      $table - The name of the table that the column is on.
                    $column - The name of the column.
                    \%new_def - The new definition for the column, in
                        C<ABSTRACT_SCHEMA> format.
       Returns:     nothing

`set_fk($table, $column \%fk_def)`

  Sets the `REFERENCES` item on the specified column.

`set_index($table, $name, $definition)`

       Description: Changes the definition of an index in this Schema object.
                    If the index doesn't exist, it will be added.
                    The table that you specify must already exist in the Schema.
                    NOTE: This does not affect the database on the disk.
                    Use the C<Bugzilla::DB> "Schema Modification Methods"
                    if you want to do that.
       Params:      $table      - The table the index is on.
                    $name       - The name of the index.
                    $definition - A hashref or an arrayref. An index
                                  definition in C<ABSTRACT_SCHEMA> format.
       Returns:     nothing

`delete_index($table, $name)`

       Description: Removes an index definition from this Schema object.
                    If the index doesn't exist, we will fail.
                    The table that you specify must exist in the Schema.
                    NOTE: This does not affect the database on the disk.
                    Use the C<Bugzilla::DB> "Schema Modification Methods"
                    if you want to do that.
       Params:      $table - The table the index is on.
                    $name  - The name of the index that we're removing.
       Returns:     nothing

`columns_equal($col_one, $col_two)`

       Description: Tells you if two columns have entirely identical definitions.
                    The TYPE field's value will be compared case-insensitive.
                    However, all other fields will be case-sensitive.
       Params:      $col_one, $col_two - The columns to compare. Hash
                        references, in C<ABSTRACT_SCHEMA> format.
       Returns:     C<1> if the columns are identical, C<0> if they are not.

# SERIALIZATION/DESERIALIZATION

`serialize_abstract()`

       Description: Serializes the "abstract" schema into a format
                    that deserialize_abstract() can read in. This is
                    a method, called on a Schema instance.
       Parameters:  none
       Returns:     A scalar containing the serialized, abstract schema.
                    Do not attempt to manipulate this data directly,
                    as the format may change at any time in the future.
                    The only thing you should do with the returned value
                    is either store it somewhere (coupled with appropriate
                    SCHEMA_VERSION) or deserialize it.

`deserialize_abstract($serialized, $version)`

       Description: Used for when you've read a serialized Schema off the disk,
                    and you want a Schema object that represents that data.
       Params:      $serialized - scalar. The serialized data.
                    $version - A number. The "version"
                        of the Schema that did the serialization.
                        See the docs for C<SCHEMA_VERSION> for more details.
       Returns:     A Schema object. It will have the methods of (and work
                    in the same fashion as) the current version of Schema.
                    However, it will represent the serialized data instead of
                    ABSTRACT_SCHEMA.

# CLASS METHODS

These methods are generally called on the class instead of on a specific object.

`get_empty_schema()`

       Description: Returns a Schema that has no tables. In effect, this
                    Schema is totally "empty."
       Params:      none
       Returns:     A "empty" Schema object.

# ABSTRACT DATA TYPES

The size and range data provided here is only intended as a guide. See your database's Bugzilla module (in this directory) for the most up-to-date values for these data types. The following abstract data types are used:

`BOOLEAN`

  Logical value 0 or 1 where 1 is true, 0 is false.

`INT1`

  Integer values (-128 - 127 or 0 - 255 unsigned).

`INT2`

  Integer values (-32,768 - 32767 or 0 - 65,535 unsigned).

`INT3`

  Integer values (-8,388,608 - 8,388,607 or 0 - 16,777,215 unsigned)

`INT4`

  Integer values (-2,147,483,648 - 2,147,483,647 or 0 - 4,294,967,295 unsigned)

`SMALLSERIAL`

  An auto-increment "INT2"

`MEDIUMSERIAL`

  An auto-increment "INT3"

`INTSERIAL`

  An auto-increment "INT4"

`TINYTEXT`

  Variable length string of characters up to 255 (2^8 - 1) characters wide.

`MEDIUMTEXT`

  Variable length string of characters up to 4000 characters wide. May be longer on some databases.

`LONGTEXT`

  Variable length string of characters up to 16M (2^24 - 1) characters wide.

`LONGBLOB`

  Variable length string of binary data up to 4M (2^32 - 1) bytes wide

`DATETIME`

  DATETIME support varies from database to database, however, it's generally safe to say that DATETIME entries support all date/time combinations greater than 1900-01-01 00:00:00. Note that the format used is `YYYY-MM-DD hh:mm:ss` to be safe, though it's possible that your database may not require leading zeros. For greatest compatibility, however, please make sure dates are formatted as above for queries to guarantee consistent results.

Database-specific subclasses should define the implementation for these data types as a hash reference stored internally in the schema object as `db_specific`. This is typically done in overridden _initialize method.

The following abstract boolean values should also be defined on a database-specific basis:

`TRUE`
`FALSE`

# SEE ALSO

Bugzilla::DB

http://www.bugzilla.org/docs/developer.html#sql-schema

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