5.7.24. Bugzilla::DB::Schema¶
5.7.24.1. NAME¶
Bugzilla::DB::Schema - Abstract database schema for Bugzilla
5.7.24.2. 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');
5.7.24.3. 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.
5.7.24.4. 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.
5.7.24.5. 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
andINDEXES
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 includePRIMARYKEY
,NOTNULL
, andDEFAULT
.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 keyFIELDS
. It may also contain the keyTYPE
, 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
, orSET 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 specifyDELETE
.
CASCADE
means that this row will be deleted along with that row.
SET NULL
means that the column will be set toNULL
when the parent row is deleted. Note that this is only valid if the column can actually be set toNULL
. (That is, the column isn'tNOT NULL
.)
UPDATE
What to do if the value in the parent table is updated. You can set this toCASCADE
orRESTRICT
, which mean the same thing as they do for `DELETE`_. This variable defaults toCASCADE
, which means "also update this column in this table."
5.7.24.6. 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 aCREATE TABLE
orALTER 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 aCREATE TABLE
orALTER TABLE
SQL statement
_get_fk_ddl
Description
Protected method. Translates theREFERENCES
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
$references
- TheREFERENCES
hashref from a column.Returns
SQL for to define the foreign key, or an empty string if$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, $column \%fk_def)
Sets theREFERENCES
item on the specified column.
set_index($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, $col_two - The columns to compare. Hash references, in C<ABSTRACT_SCHEMA> format. Returns: C<1> if the columns are identical, C<0> if they are not.
5.7.24.7. SERIALIZATION/DESERIALIZATION¶
serialize_abstract()
Description: Serializes the "abstract" schema into a format that deserialize_abstract() can read in. This is a method, called on a Schema instance. Parameters: none Returns: A scalar containing the serialized, abstract schema. Do not attempt to manipulate this data directly, as the format may change at any time in the future. The only thing you should do with the returned value is either store it somewhere (coupled with appropriate SCHEMA_VERSION) or deserialize it.
deserialize_abstract($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.
5.7.24.8. 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.
5.7.24.9. 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 isYYYY-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