用ActiveRecord連接到現有的Postgresql數據庫沒有rails

Question

我沒有使用rails，我試圖使用ActiveRecord使它更容易使用現有的數據庫。這只是一個腳本，所以我沒有database.yml或任何其他文件。我已經建立了我的數據庫連接使用

ActiveRecord::Base.establish_connection(
    adapter: 'postgresql', 
    host:  'thehosthere', 
    database: 'management', 
    username: 'management_readonly', 
    password: '', 
    port:  '5432' 
) 

我不是很熟悉數據庫，所以我只是說出我對這一個的瞭解。有相當多的模式。我感興趣的模式是具有表「主機」的管理模式。我創建了一個腳本類主持人是這樣的：

class Host < ActiveRecord::Base 
    self.table_name = "host" 
end 

我則想拉這個查詢符合條件的所有行並將其存儲到一個數組。

servers = Host.where(:realm => 'stage', :status => 'UP').pluck(:hostname) 

但我每次都收到此錯誤。

ruby environments_are_okDev.rb 
/usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql_adapter.rb:768:in `exec': PG::UndefinedTable: ERROR: relation "host" does not exist (ActiveRecord::StatementInvalid) 
LINE 5:    WHERE a.attrelid = '"host"'::regclass 
             ^
:    SELECT a.attname, format_type(a.atttypid, a.atttypmod), 
        pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, 
a.atttypmod 
       FROM pg_attribute a LEFT JOIN pg_attrdef d 
        ON a.attrelid = d.adrelid AND a.attnum = d.adnum 
       WHERE a.attrelid = '"host"'::regclass 
       AND a.attnum > 0 AND NOT a.attisdropped 
       ORDER BY a.attnum 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql_adapter.rb:768:in `exec_no_cache' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/database_statements.rb:138:in `block in exec_query' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:425:in `block in log' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activesupport-4.0.0/lib/active_support/notifications/instrumenter.rb:20:in `instrument' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:420:in `log' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/database_statements.rb:137:in `exec_query' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql_adapter.rb:915:in `column_definitions' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/schema_statements.rb:174:in `columns' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/schema_cache.rb:114:in `block in prepare_default_proc' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/schema_cache.rb:56:in `yield' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/schema_cache.rb:56:in `default' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/connection_adapters/schema_cache.rb:56:in `columns' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/model_schema.rb:208:in `columns' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/model_schema.rb:247:in `column_names' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:60:in `block in method_missing' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/relation.rb:270:in `scoping' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:60:in `method_missing' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/relation/calculations.rb:152:in `block in pluck' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/relation/calculations.rb:151:in `map!' 
     from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-4.0.0/lib/active_record/relation/calculations.rb:151:in `pluck' 
     from environments_are_okDev.rb:51:in `run' 
     from environments_are_okDev.rb:97:in `<main>' 

我真的不明白爲什麼會這樣，所以我試圖查看數據庫的樣子與此命令ActiveRecord::Base.connection.tables但我得到的是一個空數組。我不確定會發生什麼。我顯然做錯了什麼，我只是無法弄清楚什麼。請記住，這全部在一個文件腳本中。

編輯：

所以我可以看到模式，如果我用ActiveRecord::Base.connection.schema_names。這給了我一個數組=> ["db_stats", "management", "management_audit", "public"]使用pgadmin，我知道我想要的表在管理中，那麼如何訪問它？

Answer 1

嘗試增加schema_search_path當你調用establish_connection：

ActiveRecord::Base.establish_connection(
    adapter: 'postgresql', 
    host:  'thehosthere', 
    database: 'management', 
    username: 'management_readonly', 
    password: '', 
    port:  5432, 
    schema_search_path: 'management' # <-- ??? 
)