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SQL::Schema::Constraint

Section: User Contributed Perl Documentation (3)
Updated: perl v5.6.0
Index

NAME

SQL::Schema::Constraint - A constraint of a database table

SYNOPSIS

  my $constraint = SQL::Schema::Constraint->new(%attr);

  my $sql = $constraint->constraint_clause;  print $sql;

  print "$constraint";

DESCRIPTION

`SQL::Schema::Constraint' is a class for objects representing a databasetable's constraint. The methods of an instanciated object do allow to access theinformation within a database's data dictionary and to represent them as SQLcreate statements and the like using the proper SQL dialect.

Constructors

  $constraint = SQL::Schema::Constraint->new(%attr);

The new method instanciates a constraint object. The object isan in memory representation of a (possible) database table's constraint.The attributes are given as key value pairs by the hash `%attr'.Possible keys are:

  key                required?   value description

  constraint_name    yes         the constraint's name  constraint_type    yes         one of                                   C for check                                   P for primary key                                   U for unique key                                   R for referential integrity  search_condition   no          text of search condition for                                 table check  delete_rule        (*)         either `cascade' or `no action'                                 default: `no action'  status             no          either `enabled' or `disabled'                                 default: `enabled'  deferrable         no          either `deferrable' or `not deferrable'                                 default: `not deferrable'  deferred           no          either `immediate' or `deferred'                                 default: `immediate'  generated          no          either `generated name' or `user name'                                 default: `user name'  validated          no          either `validated' or `not validated'                                 default: `validated'

These keys (except columns) and their possible values correspondexactly to the data dictionary view `user_constraints' and aredescribed within Oracle's Server Reference.

Additionally the following keys are possible/required. They do notrelate to columns within the view `user_constraints'.

  key                required?   value description

  columns            no          a reference to a list with                                 column objects  r_schema           (*)         the referenced table's schema  r_table_name       (*)         the referenced table's name  r_columns          (*)         a reference to a list containing                                 column objects representing the                                 referenced columns

  (*) means: required for referential constrains otherwise not             allowed

  @columns = SQL::Schema::Constraint->select_columns($dbh,$schema,$name);

Returns a list of columns in the correct sequence. All the columnsbelonging to the constraint with the name `$schema.$name' are selectedfrom the database and returned. All the elements of the returned listare objects of the class `SQL::Schema::Table::Column'.

The method's arguments are as follows:

`$dbh': A database handle as defined by DBI(3).
`$schema': The name of the constraint's schema.
`$name': The constraint's name.

  $constraint = SQL::Schema::Constraint->select($dbh,$constraint_name);

The select method fetches the attributes required by newfrom the database and returns the constraint object. (It calls newinternally.)

If the constraint could not be found within the database, the methodreturns undef.

The method's arguments are as follows:

`$dbh': A database handle as defined by DBI(3).
`$constraint_name': The name of the constraint.

Methods

The following attribute methods do return the current valueof the attributes (as handed over to the new method):

  $constraint_name   = $constraint->name;  $constraint_type   = $constraint->type;  $search_condition  = $constraint->search_condition;  $delete_rule       = $constraint->delet_rule;  $status            = $constraint->status;  $deferrable        = $constraint->deferrable;  $deferred          = $constraint->deferred;  $generated         = $constraint->generated;  $validated         = $constraint->validated;  @columns           = $constraint->columns;  $r_schema          = $constraint->r_schema;  $r_table_name      = $constraint->r_table_name;  @r_columns         = $constraint->r_columns;

The return value of many of the above extra values is text with justtwo possible values. Sometimes it is more comfortable for programmersto have methods returning boolean values. The table below namesextra methods based on the methods above. They return `1' if thebase method returns the value shown within the 3rd column. Otherwisethe return `0'.

  extra method     base method    1 if eq          0 if eq

  cascade          delete_rule   cascade          no action  enabled          status        enabled          disabled  deferrable_b     deferrable    deferrable       not deferrable  deferred_b       deferred      deferred         immediate  generated_b      generated     generated name   user name  validated_b      validated     validated        not validated

Examples:

  $bool = $constraint->cascade;  $bool = $constraint->enabled;  $bool = $constraint->deferrable_b;  $bool = $constraint->deferred_b;  $bool = $constraint->generated_b;  $bool = $constraint->validated_b;

  $sql = $constraint->constraint_clause;  $sql = "$constraint";

Returns a string containing the constraint clause which could be usedas part of an SQL statements for creation of the corresponding constraint.This method is overloaded with the string operator. So the two examplesabove are equivalent.

AUTHOR AND COPYRIGHT

  SQL::Schema::Constraint is Copyright (C) 2000,    Torsten Hentschel    Windmuehlenweg 47    44141 Dortmund    Germany

    Email: toddAATTbayleys.ping.de

  All rights reserved.

  You may distribute this package under the terms of either the GNU  General Public License or the Artistic License, as specified in the  Perl README file.

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