Why aren'y my associations created properly in Ruby/Sequel?

Question

I am trying to build a database that has two principal tables build from csv input and link them together, but the associations are seemingly not being made – that is querying Language to get the family they belong returns nil every time. I am either missing how Sequel works, or how should associations be construed in general.

My input data is:

language_families_csv

level	family_code	parent_code	meta_comment
1	INE		Indo-European
2	BAT	INE	Baltic
3	wes-BAT	BAT	Western Baltic
3	eas-BAT	BAT	Eastern Baltic
2	HYX	INE	Armenian
2	CEL	INE	Celtic
2	SLA	INE	Slavic
3	ZLE	SLA	East Slavic
3	ZLS	SLA	South Slavic
4	eas-ZLS	ZLS	Eastern South Slavic
4	wes-ZLS	ZLS	Western South Slavic
3	ZLW	SLA	West
4	leh-ZLW	ZLW	Lechitic
4	cze-ZLW	ZLW	Czech-Slovak
4	WEN	ZLW	Sorbian

languages_csv

language_code	parent_family	meta_comment
ENG	GMW	English
FRA	ROA	French
GER	GMW	German
SPA	ROA	Spanish
POL	leh-ZLW	Polish
CES	cze-ZLW	Czech
RUS	eas-ZLS	Russian
UKR	eas-ZLS	Ukrainian
BEL	eas-ZLS	Belarusian
CSB	leh-ZLW	Kashubian
POX	leh-ZLW	Polabian
SLK	cze-ZLW	Slovak

My schema:

module Language_to_LanguageFamily
    def self.included(base)
        base.one_to_many :languages, key: :parent_family, class: :Language
        base.many_to_one :parent_family, class: :LanguageFamily, key: :family_code, primary_key: :family_code
    end
end  


### Language_Families ###
MyDB.create_table :Language_Families do
    primary_key :language_family_id
    Integer :level, index: true, null: false
    String :family_code, size: 7, index: true, null: false, unique: true
    String :meta_comment, text: true
    
    # with a self-referential association to the primary key
    foreign_key :parent_code, :Language_Families, key: :language_family_id
end

class LanguageFamily < Sequel::Model
    plugin :timestamps, update_on_create: true, force: true
    plugin :json_serializer
    plugin :validation_helpers

    # self-referrential association
    one_to_many :children, class: :LanguageFamily, key: :parent_code
    many_to_one :parent, class: :LanguageFamily, key: :parent_code

    # external associations
    include Language_to_LanguageFamily
end

### Languages ###
MyDB.create_table :Languages do
    primary_key :language_id
    String :language_code, size: 7, index: true, null: false, unique: true
    String :meta_comment, text: true

    # ↓ optional association
    foreign_key :parent_family, :Language_Families, key: :family_code, null: true, default: nil
end

class Language < Sequel::Model
    plugin :timestamps, update_on_create: true, force: true
    plugin :json_serializer
    plugin :validation_helpers
    
    # external associations
    include Language_to_LanguageFamily

    # ↓ allows accessing foreign keys
    attr_accessor :parent_family
end

and my code:

require 'csv'
require 'sequel'

MyDB = Sequel.connect adapter: :sqlite, database: 'MirDB.sqlite'

MyDB.drop_table(*db.tables)

# Create an empty hash to store the id of each language family code
code_id = {}

# insert data into Language_Families DB
language_families_csv.each do |family|
    # Create a new LanguageFamily object
    language_family = LanguageFamily.new
    language_family.level = family["level"].to_i
    language_family.family_code = family["family_code"]
    language_family.meta_comment = family["meta_comment"]
    if parent_code = family["parent_code"]
        language_family.parent = LanguageFamily.find(parent_code: parent_code)
    end
    language_family.save
    code_id[language_family.family_code] = language_family.id
end

# insert data into Language DB
languages_csv.each do |lang_row|
    # Create a new Language object
    language = Language.new
    language.language_code = lang_row["language_code"]
    language.meta_comment = lang_row["meta_comment"]
    
    # set the association to the corresponding language family if present in languages
    if lang_row["parent_family"]    # ← if in languages
        lang_parent_family = LanguageFamily.first(family_code: lang_row["parent_family"])
        if lang_parent_family       # ← if such family exists
            language.parent_family = lang_parent_family
            # puts "#{language.parent_family} ↔ #{lang_parent_family.family_code}"
        else
            puts 'Family '.red + lang_parent_family.family_code.cyan + ' doesn’t exist!'.red
        end
    end
    
    language.save
end

Finally, when I run puts Language.all.to_s, all I get is:

[
    #<Language @values={:language_id=>1, :language_code=>"ENG", :meta_comment=>"English", :parent_family=>nil}>,
    #<Language @values={:language_id=>2, :language_code=>"FRA", :meta_comment=>"French", :parent_family=>nil}>,
    #<Language @values={:language_id=>3, :language_code=>"GER", :meta_comment=>"German", :parent_family=>nil}>,
    #<Language @values={:language_id=>4, :language_code=>"SPA", :meta_comment=>"Spanish", :parent_family=>nil}>,
    #<Language @values={:language_id=>5, :language_code=>"POL", :meta_comment=>"Polish", :parent_family=>nil}>,
    #<Language @values={:language_id=>6, :language_code=>"CES", :meta_comment=>"Czech", :parent_family=>nil}>,
    #<Language @values={:language_id=>7, :language_code=>"RUS", :meta_comment=>"Russian", :parent_family=>nil}>,
    #<Language @values={:language_id=>8, :language_code=>"UKR", :meta_comment=>"Ukrainian", :parent_family=>nil}>,
    #<Language @values={:language_id=>9, :language_code=>"BEL", :meta_comment=>"Belarusian", :parent_family=>nil}>,
    #<Language @values={:language_id=>10, :language_code=>"CSB", :meta_comment=>"Kashubian", :parent_family=>nil}>,
    #<Language @values={:language_id=>11, :language_code=>"POX", :meta_comment=>"Polabian", :parent_family=>nil}>,
    #<Language @values={:language_id=>12, :language_code=>"SLK", :meta_comment=>"Slovak", :parent_family=>nil}>,
    (…)
]

Answer 1

I've uncomplicated your set up a bit. You have to make sure your code works, before you start extracting modules, it makes it that much harder to figure out what's going on. Also this is my first time using Sequel.

require "sequel"
require "csv"

db = Sequel.connect("sqlite://language.db")
db.drop_table(*db.tables)

#     language_families             languages
#     .---------------.        .---------------.
# .-->| code       pk |<---.   | code       pk |
# |   | name          |    |   | name          |
# |   | level         |    `---| family_id  fk |
# `---| parent_id  fk |        `---------------`
#     `---------------`

db.create_table :language_families do
  String  :code, primary_key: true
  Integer :level
  String  :name      # `meta_comment` sure looks like `name` to me
  String  :parent_id # primary_key is a string so this is a string
end

db.create_table :languages do
  String :code, primary_key: true
  String :name
  String :family_id
end

# you should avoid unnecessary prefixes, if you can:
# `family_code` in LanguageFamily, just `code` is sufficient
# `language_code` in Language, just `code` is sufficient
# `parent_family` in Language, just `family` is sufficient
# otherwise everything will be `parent_something` and `something_code`

# so far, i've learned this much:                     ActiveRecord equivalent:
# one_to_many                                         has_many
#   key:         column from the other table            foreign_key
#   primary_key: column from the current table          primary_key
#
# many_to_one                                         belongs_to
#   key:         column from the current table          foreign_key
#   primary_key: column from the other table            primary_key 

# I don't see how `Language_to_LanguageFamily` can work for both models 

class LanguageFamily < Sequel::Model
  unrestrict_primary_key # because we need to assign primary key - `code`

  many_to_one :parent,   class: :LanguageFamily
  one_to_many :children, class: :LanguageFamily, key: :parent_id

  one_to_many :languages, key: :family_id

  # making a full tree structure is more involved than parent/children
  # relationships, this is just for a quick set up
  def descendants
    [self, children.map(&:descendants)].flatten
  end

  def descendant_languages
    Language.where(family_id: descendants.map(&:code)).all
  end
end

class Language < Sequel::Model
  unrestrict_primary_key

  many_to_one :family, class: :LanguageFamily

  # from included module, i'm not sure how language has more languages, but if
  # you mean other languages from the same family
  def sibling_languages
    return [] unless family 
    family.languages.reject { |lang| lang.code == self.code }
  end
end

puts "==> Loading language families"
CSV.table("language_families.csv").each do |row|
  language_family = LanguageFamily.new({
    code:   row[:family_code],
    level:  row[:level],
    name:   row[:meta_comment],
    # this will set `parent_id`
    parent: LanguageFamily.find(code: row[:parent_code])
  })

  p language_family.save
end

puts "==> Loading languages"
CSV.table("languages.csv").each do |row|
  language = Language.new({
    code:   row[:language_code],
    name:   row[:meta_comment],
    # this will set `family_id`
    family: LanguageFamily.find(code: row[:parent_family])
  })

  # # if you want to do this as a separate step
  # if (family = LanguageFamily.find(code: row[:parent_family]))
  #   language.family = family
  # else
  #   puts "Family #{row[:parent_family]} doesn't exist!"
  # end

  p language.save
end

Test:

>> LanguageFamily.last.parent
=> #<LanguageFamily @values={:code=>"ZLS", :level=>3, :name=>"South Slavic", :parent_id=>"SLA"}>

>> LanguageFamily.find(code: "leh-ZLW").languages
=> [#<Language @values={:code=>"POL", :name=>"Polish", :family_id=>"leh-ZLW"}>,
    #<Language @values={:code=>"CSB", :name=>"Kashubian", :family_id=>"leh-ZLW"}>,
    #<Language @values={:code=>"POX", :name=>"Polabian", :family_id=>"leh-ZLW"}>]

>> LanguageFamily.find(code: "ZLW").languages
=> [] # no languages in this family, but plenty in child families
>> LanguageFamily.find(code: "ZLW").descendant_languages
=> [#<Language @values={:code=>"POL", :name=>"Polish", :family_id=>"leh-ZLW"}>,
    #<Language @values={:code=>"CES", :name=>"Czech", :family_id=>"cze-ZLW"}>,
    #<Language @values={:code=>"CSB", :name=>"Kashubian", :family_id=>"leh-ZLW"}>,
    #<Language @values={:code=>"POX", :name=>"Polabian", :family_id=>"leh-ZLW"}>,
    #<Language @values={:code=>"SLK", :name=>"Slovak", :family_id=>"cze-ZLW"}>]
#                                i guess you can also do "LIKE '%-ZLW'" ^

>> LanguageFamily.find(code: "ZLW").parent.parent.descendants.count
=> 15

>> Language.find(code: "POL").sibling_languages
=> [#<Language @values={:code=>"CSB", :name=>"Kashubian", :family_id=>"leh-ZLW"}>, 
    #<Language @values={:code=>"POX", :name=>"Polabian", :family_id=>"leh-ZLW"}>]

---

Import test:

>> load "app.rb"
==> Loading language families
#<LanguageFamily @values={:code=>"INE", :level=>1, :name=>"Indo-European", :parent_id=>nil}>
#<LanguageFamily @values={:code=>"BAT", :level=>2, :name=>"Baltic", :parent_id=>"INE"}>
#<LanguageFamily @values={:code=>"wes-BAT", :level=>3, :name=>"Western Baltic", :parent_id=>"BAT"}>
#<LanguageFamily @values={:code=>"eas-BAT", :level=>3, :name=>"Eastern Baltic", :parent_id=>"BAT"}>
#<LanguageFamily @values={:code=>"HYX", :level=>2, :name=>"Armenian", :parent_id=>"INE"}>
#<LanguageFamily @values={:code=>"CEL", :level=>2, :name=>"Celtic", :parent_id=>"INE"}>
#<LanguageFamily @values={:code=>"SLA", :level=>2, :name=>"Slavic", :parent_id=>"INE"}>
#<LanguageFamily @values={:code=>"ZLE", :level=>3, :name=>"East Slavic", :parent_id=>"SLA"}>
#<LanguageFamily @values={:code=>"ZLS", :level=>3, :name=>"South Slavic", :parent_id=>"SLA"}>
#<LanguageFamily @values={:code=>"eas-ZLS", :level=>4, :name=>"Eastern South Slavic", :parent_id=>"ZLS"}>
#<LanguageFamily @values={:code=>"wes-ZLS", :level=>4, :name=>"Western South Slavic", :parent_id=>"ZLS"}>
#<LanguageFamily @values={:code=>"ZLW", :level=>3, :name=>"West", :parent_id=>"SLA"}>
#<LanguageFamily @values={:code=>"leh-ZLW", :level=>4, :name=>"Lechitic", :parent_id=>"ZLW"}>
#<LanguageFamily @values={:code=>"cze-ZLW", :level=>4, :name=>"Czech-Slovak", :parent_id=>"ZLW"}>
#<LanguageFamily @values={:code=>"WEN", :level=>4, :name=>"Sorbian", :parent_id=>"ZLW"}>

==> Loading languages
#<Language @values={:code=>"ENG", :name=>"English", :family_id=>nil}>
#<Language @values={:code=>"FRA", :name=>"French", :family_id=>nil}>
#<Language @values={:code=>"GER", :name=>"German", :family_id=>nil}>
#<Language @values={:code=>"SPA", :name=>"Spanish", :family_id=>nil}>
#<Language @values={:code=>"POL", :name=>"Polish", :family_id=>"leh-ZLW"}>
#<Language @values={:code=>"CES", :name=>"Czech", :family_id=>"cze-ZLW"}>
#<Language @values={:code=>"RUS", :name=>"Russian", :family_id=>"eas-ZLS"}>
#<Language @values={:code=>"UKR", :name=>"Ukrainian", :family_id=>"eas-ZLS"}>
#<Language @values={:code=>"BEL", :name=>"Belarusian", :family_id=>"eas-ZLS"}>
#<Language @values={:code=>"CSB", :name=>"Kashubian", :family_id=>"leh-ZLW"}>
#<Language @values={:code=>"POX", :name=>"Polabian", :family_id=>"leh-ZLW"}>
#<Language @values={:code=>"SLK", :name=>"Slovak", :family_id=>"cze-ZLW"}>
=> true