Ruby rails - 从数据库中只选择几列
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Ruby rails - select only few columns from the data base
提问by Kapish M
What is the way in rails to structure sql query to only select certain columns from the database, I have some large data fields which I want to avoid loading from continuous periodic ajax calls. Reading unnecessarily is resource consuming and slow.
rails 构造 sql 查询以仅从数据库中选择某些列的方式是什么，我有一些大数据字段，我想避免从连续的定期 ajax 调用中加载。不必要的阅读是资源消耗和缓慢的。
@itemlist = Item.find(:all, :conditions => { .... } ) #this select all columns
I am looking for SELECT name, address FROM users;instead of SELECT * FROM users;
我正在寻找SELECT name, address FROM users;而不是SELECT * FROM users;
回答by nyaa
Rails 3:
轨道 3：
Item.select("name, address").where( .... )
Item.select("name, address").where( .... )
回答by dku.rajkumar
Make use of :selectconstruct. Try this:
利用:select构造。尝试这个：
@itemlist = Item.select('name, address', conditions: { .... } )
For previous version of Rails:
对于以前版本的 Rails：
@itemlist = Item.find(:all,:select => 'name, address', :conditions => { .... } )
回答by Michelle Tilley
Using Arel (aka in Rails 3), use:
使用 Arel（在 Rails 3 中又名），使用：
Item.where(...).select("name, address")
Also, it seems .select gets ignored if you tack on a scope that has an :include => ...
此外，如果您添加具有 :include => ... 的范围，似乎 .select 会被忽略。
回答by Kuberan
@itemlist = Item.select('name, address').where(...#some condition)
回答by coder_tim
Try this:
尝试这个：
@itemlist = Item.find(:all, :select => "name, address", :conditions => { .... } )
回答by eriel marimon
If want to select specific columns from the rails console, pluck(will work.
Example:
如果要从 中选择特定列rails console，pluck(将起作用。例子：
2.4.1 :007 > User.connection
2.4.1 :006 > User.all.pluck(:email)
(0.3ms) SELECT `users`.`email` FROM `users`
=> ["[email protected]", "[email protected]"]
Note that this will also work from within the Rails app.
请注意，这也适用于 Rails 应用程序。
