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DataMapper plugin constraining relationships

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dm-constraints.gemspec

README.rdoc

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 Farmer

has n, :pigs #equivalent to: has n, :pigs, :constraint => :protect

end

# M:M Example class Articles

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 Farmer

has 1, :beloved_sheep, :constraint => :protect

end

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