【问题标题】：ActiveRecord finding record by relations requiring all attributesActiveRecord 通过需要所有属性的关系查找记录
【发布时间】：2015-11-25 06:57:54
【问题描述】：

好的，所以我是 ruby 和 rails 的新手，我的问题可能会显示出来。

我正在编写一个有趣的应用程序，并且有一个关于在 HABTM 关系中查找记录的特别奇怪的问题。底层数据库是Postgresql

我的模型如下所示

class Family < ActiveRecord::Base
  has_and_belongs_to_many :persons
end

class Person < ActiveRecord::Base
  has_and_belongs_to_many :families
end

假设我有 4 个人“乔”、“简”、“玛丽”、“本”。他们都可以属于多个家庭。

Family 1 << 'Joe', 'Jane', 'Ben'

Family 2 << 'Jane', 'Ben'

Family 3 << 'Joe', 'Jane', 'Ben', 'Mary'

我希望能够通过搜索他们的名字找到家人

这就是我的查询当前的样子

Family.joins(:persons).where(persons: {name:['Joe','Jane','Ben']})

这非常适合查找包含 Joe、Jane 或 Ben（所有家庭）的所有记录，但不适用于返回只有 Joe、Jane 和 Ben 的记录。

在我的示例中，我只查找家庭 1，而不是其他 2。

我如何确保只找到包含所有名称的记录，不多也不少。

是否有更好的查询要编写或者我应该重新考虑我的数据库结构？

【问题讨论】：

标签： ruby-on-rails ruby postgresql activerecord

【解决方案1】：

我会这样设置模型：

class Family < ActiveRecord::Base
  has_many :persons
end

class Person < ActiveRecord::Base
  belongs_to :family
end

然后将family_id添加到family表中。

现在您可以拨打family.first.persons

或者

Family.where(id: 1).first.persons

另外，如果您觉得这种方法不合适，那么我建议您使用has_many :through 而不是has_many_and_belongs_to

【讨论】：

【解决方案2】：

所以在对#rubyonrails irc 进行了一些挖掘和一些帮助之后，我想出了这个解决方案。

class Family < ActiveRecord::Base

  def self.find_by_person_names(persons = [])
    family = nil
    families = Family.joins(:persons).where(persons: {name:persons})
    families.each do |f|
      if f.persons.names.sort == persons.sort
        family = f
      end
    end
    return family
  end
end

【讨论】：

【解决方案3】：

我也认为 has_many through 关系更适合：has_and_belongs_to_many vs has_many through

这是一个不需要在 ruby 中过滤结果的选项：

选择其中包含每个所需人员的所有 FamilyPerson 对象
选择所有 FamilyPerson 对象中的人不是所需的人
在第一个查询结果而不是第二个查询结果中选择所有具有 ID 的 Family 对象 - 换句话说，那些拥有所有必要人员但没有更多人的家庭

实施

app/models/family.rb

class Family < ActiveRecord::Base
  has_many :family_people
  has_many :people, through: :family_people

  def self.all_with_members members
    member_ids = members.collect {|m| m.id }

    # FamilyPersons that have each of the members in it
    enough = FamilyPerson.where(person_id: member_ids).group("family_id").having("count(person_id) >= ?", member_ids.count).collect { |fp| fp.family_id }

    # FamilyPersons that have no additional members
    too_many = FamilyPerson.where("person_id NOT IN(?)", member_ids).group("family_id").having("count(person_id) > 0").collect { |fp| fp.family_id }

    Family.find enough - too_many
  end
end

app/models/person.rb

class Person < ActiveRecord::Base
  has_many :family_people
  has_many :families, through: :family_people
end

app/models/family_person.rb

class FamilyPerson < ActiveRecord::Base
  belongs_to :family
  belongs_to :person
end

摘自 db/schema.rb

create_table "families", force: true do |t|
  t.string "name"
end

create_table "family_people", force: true do |t|
  t.integer "person_id"
  t.integer "family_id"
end

create_table "people", force: true do |t|
  t.string "name"
end

测试

spec/models/family_spec.rb

使用 RSpec 进行测试

require 'rails_helper'

describe Family do
  before :each do
    Rails.application.load_seed
  end

  describe "self.all_with_members" do
    it "returns all families that have each person in it" do
      people = [Person.find_by_name("Joe"), Person.find_by_name("Jane"), Person.find_by_name("Ben")]
      expect(Family.all_with_members(people).to_a).to eq Family.where(name: "Family 1").to_a
    end
  end
end

db/seeds.rb

种子数据

Family.destroy_all
Person.destroy_all
FamilyPerson.destroy_all

joe = Person.create name: "Joe"
jane = Person.create name: "Jane"
ben = Person.create name: "Ben"
mary = Person.create name: "Mary"

family_one = Family.create name: "Family 1"
family_two = Family.create name: "Family 2"
family_three = Family.create name: "Family 3"

family_one.people << joe
family_one.people << jane
family_one.people << ben
family_one.save!

family_two.people << jane
family_two.people << ben
family_two.people << mary
family_two.save!

family_three.people << joe
family_three.people << jane
family_three.people << ben
family_three.people << mary
family_three.save!

【讨论】：