sbf-dm-constraints

= dm-constraints

Plugin that adds foreign key constraints to associations. Currently supports only PostgreSQL and MySQL

All constraints are added to the underlying database, but constraining is implemented in pure ruby.

=== Constraints

• :protect returns false on destroy if there are child records
• :destroy deletes children if present
• :destroy! deletes children directly without instantiating the resource, bypassing any hooks Does not support 1:1 Relationships as #destroy! is not supported on Resource in dm-master
• :set_nil sets parent id to nil in child associations Not valid for M:M relationships as duplicate records could be created (see explanation in specs)
• :skip Does nothing with children, results in orphaned records

By default a relationship will PROTECT its children.

=== Cardinality Notes

• 1:1

• Applicable constraints: [:set_nil, :skip, :protect, :destroy]

• 1:M

• Applicable constraints: [:set_nil, :skip, :protect, :destroy, :destroy!]

• M:M

• Applicable constraints: [:skip, :protect, :destroy, :destroy!]

=== Examples

1:M Example

class Post has n, :comments # equivalent to: # has n, :comments, :constraint => :protect end

M:M Example

class Article has n, :tags, :through => Resource, :constraint => :destroy end

class Tags has n, :articles, :through => Resource, :constraint => :destroy end

Intermediary constraints for relationships using :through => Resource

are automatically inherited from the M:M relationship.

1:1 Example

class User has 1, :address, :constraint => :protect end