Method: Sequel::Database#create_join_table

Defined in:
lib/sequel/database/schema_methods.rb

#create_join_table(hash, options = OPTS) ⇒ Object

Create a join table using a hash of foreign keys to referenced table names. Example:

create_join_table(cat_id: :cats, dog_id: :dogs)
# CREATE TABLE cats_dogs (
#  cat_id integer NOT NULL REFERENCES cats,
#  dog_id integer NOT NULL REFERENCES dogs,
#  PRIMARY KEY (cat_id, dog_id)
# )
# CREATE INDEX cats_dogs_dog_id_cat_id_index ON cats_dogs(dog_id, cat_id)

The primary key and index are used so that almost all operations on the table can benefit from one of the two indexes, and the primary key ensures that entries in the table are unique, which is the typical desire for a join table.

The default table name this will create is the sorted version of the two hash values, joined by an underscore. So the following two method calls create the same table:

create_join_table(cat_id: :cats, dog_id: :dogs) # cats_dogs
create_join_table(dog_id: :dogs, cat_id: :cats) # cats_dogs

You can provide column options by making the values in the hash be option hashes, so long as the option hashes have a :table entry giving the table referenced:

create_join_table(cat_id: {table: :cats, type: :Bignum}, dog_id: :dogs)

You can provide a second argument which is a table options hash:

create_join_table({cat_id: :cats, dog_id: :dogs}, temp: true)

Some table options are handled specially:

:index_options

The options to pass to the index

:name

The name of the table to create

:no_index

Set to true not to create the second index.

:no_primary_key

Set to true to not create the primary key.



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# File 'lib/sequel/database/schema_methods.rb', line 119

def create_join_table(hash, options=OPTS)
  keys = hash.keys.sort
  create_table(join_table_name(hash, options), options) do
    keys.each do |key|
      v = hash[key]
      unless v.is_a?(Hash)
        v = {:table=>v}
      end
      v[:null] = false unless v.has_key?(:null)
      foreign_key(key, v)
    end
    primary_key(keys) unless options[:no_primary_key]
    index(keys.reverse, options[:index_options] || OPTS) unless options[:no_index]
  end
  nil
end