我有一个预先存在的postgres数据库，我试图查询。我设置了两个模型，即客户和设备。我试图查询两个用非标准密钥连接它们的表。无论我尝试过什么，我只从一张桌子上取回结果。我尝试更改ActiveRecord行为以使用非标准密钥以及find_by_sql（）。由于现有的表结构，我还禁用了默认表复数。我错过了一些明显的东西吗？
ActiveRecord::Base.pluralize_table_names = false
class Customer < ActiveRecord::Base
self.primary_key = :acct
has_many :equipment, foreign_key: 'acct'
end
class Equipment < ActiveRecord::Base
self.primary_key = :acct
belongs_to :customer, foreign_key: 'acct'
end
me@nc:~/rails_workspace/pg_test$ rails c
Loading development environment (Rails 4.2.0.rc2)
2.2.1 :001 > Customer.first()
Customer Load (16.9ms) SELECT "customer".* FROM "customer" ORDER BY "customer"."acct" ASC LIMIT 1
=> #<Customer acct: "000002", franchise: "501", name: "NAME", address: "STREET ADDR", city: "CITY", state: "ST", zip: "ZIPCODE", phone: "1234567890", email: "email@domain.com", installdate: "2014-02-20", consumptiondate: nil, parent: "", sentoverage: false, exempt: false, pin: "", locked: false, status: "ACT">
2.2.1 :002 > Equipment.first()
Equipment Load (128.3ms) SELECT "equipment".* FROM "equipment" ORDER BY "equipment"."acct" ASC LIMIT 1
=> #<Equipment mac: "26225070", acct: "000002">
2.2.1 :003 >
2.2.1 :009 > Customer.find_by_sql("Select c.*, e.* from customer as c, equipment as e where e.acct = c.acct and c.acct = '000002' limit 1")
Customer Load (53.9ms) Select c.*, e.* from customer as c, equipment as e where e.acct = c.acct and c.acct = '000002' limit 1
=> [#<Customer acct: "000002", franchise: "501", name: "NAME", address: "STREET ADDR", city: "CITY", state: "ST", zip: "ZIPCODE", phone: "1234567890", email: "email@domain.com", installdate: "2014-02-20", consumptiondate: nil, parent: "", sentoverage: false, exempt: false, pin: "", locked: false, status: "ACT">]
2.2.1 :010 > Customer.joins('FULL OUTER JOIN equipment ON equipment.acct = customer.acct').limit(1)
Customer Load (119.9ms) SELECT "customer".* FROM "customer" FULL OUTER JOIN equipment ON equipment.acct = customer.acct LIMIT 1
=> #<ActiveRecord::Relation [#<Customer acct: "000002", franchise: "501", name: "NAME", address: "STREET ADDR", city: "CITY", state: "ST", zip: "ZIPCODE", phone: "1234567890", email: "email@domain.com", installdate: "2014-02-20", consumptiondate: nil, parent: "", sentoverage: false, exempt: false, pin: "", locked: false, status: "ACT">]>
2.2.1 :011 > Customer.joins(:equipment)
ActiveRecord::ConfigurationError: Association named 'equipment' was not found on Customer; perhaps you misspelled it?
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/associations/join_dependency.rb:218:in `find_reflection'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/associations/join_dependency.rb:223:in `block in build'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/associations/join_dependency.rb:222:in `each'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/associations/join_dependency.rb:222:in `map'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/associations/join_dependency.rb:222:in `build'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/associations/join_dependency.rb:99:in `initialize'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/relation/query_methods.rb:1039:in `new'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/relation/query_methods.rb:1039:in `build_joins'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/relation/query_methods.rb:863:in `build_arel'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/relation/query_methods.rb:855:in `arel'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/relation.rb:638:in `exec_queries'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/relation.rb:514:in `load'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/relation.rb:243:in `to_a'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activerecord-4.2.0.rc2/lib/active_record/relation.rb:629:in `inspect'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/railties-4.2.0.rc2/lib/rails/commands/console.rb:110:in `start'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/railties-4.2.0.rc2/lib/rails/commands/console.rb:9:in `start'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/railties-4.2.0.rc2/lib/rails/commands/commands_tasks.rb:68:in `console'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/railties-4.2.0.rc2/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/railties-4.2.0.rc2/lib/rails/commands.rb:17:in `<top (required)>'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `require'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `block in require'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:240:in `load_dependency'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:274:in `require'
from /home/me/rails_workspace/pg_test/bin/rails:8:in `<top (required)>'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `load'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `block in load'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:240:in `load_dependency'
from /home/me/.rvm/gems/ruby-2.2.1@pg_test/gems/activesupport-4.2.0.rc2/lib/active_support/dependencies.rb:268:in `load'
from /home/me/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/me/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from -e:1:in `<main>'2.2.1 :012 >
修改
修改了设备类，将belongs_to：设备更改为：设备。导致修复ActiveRecord :: ConfigurationError：名为＆＃39;设备＆＃39;错误。但仍无法解决加入问题。如果我使用＆＃34;键＆＃34;手动查询Equipment表。在Customer表中，找到了数据记录。
2.2.1 :008 > Customer.joins(:equipment).limit(1)
Customer Load (11.9ms) SELECT "customer".* FROM "customer" INNER JOIN "equipment" ON "equipment"."acct" = "customer"."acct" LIMIT 1
=> #<ActiveRecord::Relation > [#<Customer acct: "000002", franchise: "501", name: "NAME", address: "STREET ADDR", city: "CITY", state: "ST", zip: "ZIPCODE", phone: "1234567890", email: "email@domain.com", installdate: "2014-02-20", consumptiondate: nil, parent: "", sentoverage: false, exempt: false, pin: "", locked: false, status: "ACT">]
2.2.1 :017 > Equipment.where(acct: '000002')
Equipment Load (76.5ms) SELECT "equipment".* FROM "equipment" WHERE "equipment"."acct" = $1 [["acct", "000002"]]
=> #<ActiveRecord::Relation [#<Equipment mac: "26225070", acct: "000002">, #<Equipment mac: "23126536", acct: "000002">, #<Equipment mac: "00E06F76A08A", acct: "000002">]>
答案 0 :(得分：1)
对于更简单的解决方案，在scope模型中定义by_customer Equipment，
class Equipment < ActiveRecord::Base
...
scope :by_customer,->(customer_conditions) { joins(:customer).where(customer: customer_conditions)}
end
并关注scope模型中的by_equipment Customer，
class Customer < ActiveRecord::Base
...
scope :by_equipment,->(equipment_conditions) { joins(:equipment).where(equipment: equipment_conditions)}
end
查找客户设备＆＃39; 000002＆＃39;
@equipments = Equipment.by_customer(acct: '000002')
要找到拥有mac地址设备的客户是＆＃39; 26225070＆＃39;
@customer = Customer.by_equipment(mac: '26225070')
答案 1 :(得分：0)
我想我可能会看到你缺少的东西。
Customer.joins(:anything)将返回Customer。
Equipment.joins(:anything)将返回Equipment。
也许你已经明白了，但也许不是。
如果你想要一个两者混合的结果集，我认为你必须完全从一个不同的角度来看待它，我想我需要更好地理解你最终的结果。为了能够提供任何好的建议。
修改以获取属于特定客户的设备：
Equipment.joins(:customer).where('customer.acct = ?', '000002')
为客户提供设备mac：
Customer.joins(:equipment).where('equipment.mac = ?', '26225070')