---
name: "Alzabo::ForeignKey"
section: "3pm"
platform: "linux"
package: "libalzabo-perl"
version: "0.92-6"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Alzabo::ForeignKey"
---

# Alzabo::ForeignKey(3pm)

Foreign key (relation) objects

## NAME

Alzabo::ForeignKey - Foreign key (relation) objects

## SYNOPSIS

```
  use Alzabo::ForeignKey;
  foreach my $fk ($table->foreign_keys)
  {
      print $fk->cardinality;
  }
```

## DESCRIPTION

A foreign key is an object defined by several properties.  It represents a relationship from a column or columns in one table to a column or columns in another table.

This relationship is defined by its cardinality (one to one, one to many, or many to one) and its dependencies (whether or not table X is dependent on table Y, and vice versa).

Many to many relationships are not allowed.  However, you may indicate such a relationship when using the Alzabo::Create::Schema-\>add\_relation method method, and it will create the necessary intermediate linking table for you.

## METHODS

### table\_from

### table\_to

Returns the relevant `"Alzabo::Table"` object.

### columns\_from

### columns\_to

Returns the relevant `"Alzabo::Column"` object(s) for the property as an array.

### column\_pairs

Returns an array of array references.  The references are to two column array of `"Alzabo::Column"` objects.  These two columns correspond in the tables being linked together.

### cardinality

Returns a two element array containing the two portions of the cardinality of the relationship.  Each portion will be either '1' or 'n'.

### from\_is\_dependent

### to\_is\_dependent

Returns a boolean value indicating whether there is a dependency from one table to the other.

### is\_one\_to\_one

### is\_one\_to\_many

### is\_many\_to\_one

Returns a boolean value indicating what kind of relationship the object represents.

### is\_same\_relationship\_as ($fk)

Given a foreign key object, this returns true if the two objects represent the same relationship.  However, the two objects may represent the same relationship from different table's points of view.

### id

Returns a string uniquely identifying the foreign key.

### comment

Returns the comment associated with the foreign key object, if any.

## AUTHOR

Dave Rolsky, \<autarch@urth.org\>