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You are here: Home Documentation Previous versions OME Server Developer Perl API Adding Columns

Adding Columns

Adding columns

package OME::SemanticType;

use strict;
use OME;

use OME::DBObject;
use base qw(OME::DBObject);

__PACKAGE__->addColumn(name => 'name',
                        SQLType => 'varchar(64)',
                        NotNull => 1,
                        Unique  => 1,
__PACKAGE__->addColumn(granularity => 'granularity',
                        SQLType => 'char(1)',
                        NotNull => 1,
                        Check   => "(granularity in ('G','D','I','F'))",
__PACKAGE__->addColumn(description => 'description',{SQLType => 'text'});
                     'OME::SemanticType::Element' => 'semantic_type');
Listing 1 — OME::SemanticType definition

After these preliminary calls, the package defines the columns in the database table. These columns can fall into one of four categories: primary keys, standard columns, has-one foreign keys, and has-many foreign keys. Each column has at least one alias, which is how other pieces of code refer to the column. Most of the time, the alias and the name of the underlying database column are identical, but they don't have to be. Has-many foreign keys are defined by the hasMany method. Standard columns and has-one foreign keys are both defined by the addColumn method.

Primary keys are defined by the addPrimaryKey method. The only parameter to this method is the primary key's column name; the database column is automatically assigned an SQL type of integer (or a database-vendor-specific type appropriate to primary keys), and it is automatically given NOT NULL and PRIMARY KEY SQL clauses. The primary key's alias is always id.

Standard columns are defined by the addColumn method. This method defines a database column in the default table and creates an accessor/mutator method in the current package to read that column. The name of this method is the same as the column's alias. For standard columns, the addColumn method takes in three parameters: the column's alias, the name of the database column, and a hash of SQL options. These SQL options provide the necessary information to completely define the database column. A list of valid SQL options can be found in the OME::DBObject reference page.

The SQL options parameter can be left out; doing so adds an accessor/mutator method, but prevents the database creation code from modifying the table structure. This is use-ful if you want to define more than one accessor/mutator method for a given column. If the SQL options were specified for both, the database creation code would try to place both column definitions into the generated CREATE TABLE statement. Defining two col-umns with the same name is erroneous SQL, so the database creation code would throw an error trying to create the class.

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