Ruby rails - select only few columns from the database

Question

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.

@itemlist = Item.find(:all, :conditions => { .... } ) #this select all columns

I am looking for SELECT name, address FROM users; instead of SELECT * FROM users;

Usually if you don't need/use other columns, you should think about data normalization. — Pavel S, Apr 21 '12 at 09:46

score 131 · Accepted Answer · answered Apr 21 '12 at 13:37

131

Rails 3:

Item.select("name, address").where( .... )

answered Apr 21 '12 at 13:37

nyaa

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Yup, great one! Promote this one, guys, as Rails 3 is far more popular than the 2nd one – Jackie Chan Apr 13 '13 at 13:07
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Also of note, if you have more than one table in your `SELECT` statement and you're referencing a column that could exist in more than 1 table, include the table in the select, like `select("items.name, users.address")`. – Joshua Pinter Aug 27 '14 at 16:39
Still works in Rails 7. – B Seven May 09 '23 at 14:35

score 30 · Answer 2 · edited Jul 24 '15 at 19:40

30

Make use of :select construct. Try this:

@itemlist = Item.select('name, address', conditions: { .... } )

For previous version of Rails:

@itemlist = Item.find(:all,:select => 'name, address', :conditions => { .... } )

edited Jul 24 '15 at 19:40

pranavcode

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answered Apr 21 '12 at 05:25

dku.rajkumar

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This is no longer correct and is not supported in Rails 4. Answer needs updating. – superluminary May 21 '15 at 15:21
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The answer has been updated after superluminary's comment to reflect the new .select syntax. – Matthias Winkelmann Nov 10 '15 at 20:26

score 11 · Answer 3 · edited Jul 02 '15 at 15:37

11

Using Arel (aka in Rails 3), use:

Item.where(...).select("name, address")

Also, it seems .select gets ignored if you tack on a scope that has an :include => ...

edited Jul 02 '15 at 15:37

Simon B.

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answered Apr 21 '12 at 05:26

Michelle Tilley

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score 7 · Answer 4 · answered Apr 26 '12 at 09:19

7

@itemlist = Item.select('name, address').where(...#some condition)

answered Apr 26 '12 at 09:19

Kuberan

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score 7 · Answer 5 · answered Jun 27 '18 at 01:23

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If want to select specific columns from the rails console, pluck( will work. Example:

2.4.1 :007 > User.connection
2.4.1 :006 > User.all.pluck(:email)
   (0.3ms)  SELECT `users`.`email` FROM `users`
 => ["test@test.com", "another_test@test.com"]

Note that this will also work from within the Rails app.

answered Jun 27 '18 at 01:23

eriel marimon

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I believe you can just use `User.pluck(:email)` – Fatima Aug 24 '21 at 04:21

score 3 · Answer 6 · answered Apr 21 '12 at 05:24

3

Try this:

@itemlist = Item.find(:all, :select => "name, address", :conditions => { .... } )

answered Apr 21 '12 at 05:24

coder_tim

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Ruby rails - select only few columns from the database

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