Ruby Rails - Select Only Few Columns from the Data Base

Ruby rails - select only few columns from the data base

Rails 3:

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

How to find a record by id and select few columns, ruby on rails?

You can try this. I hope this will help.

@user = User.where("id = ?", 4).select( "user_fname, user_lname")

How to select only specific columns when querying using ActiveRecord?

In your post model you can define the association as follows:

belongs_to :user, :select => [:username]

Then referring to the user via a post would select only the stated columns.

ActiveRecord find and only return selected columns

In Rails 2

l = Location.find(:id => id, :select => "name, website, city", :limit => 1)

...or...

l = Location.find_by_sql(:conditions => ["SELECT name, website, city FROM locations WHERE id = ? LIMIT 1", id])

This reference doc gives you the entire list of options you can use with .find, including how to limit by number, id, or any other arbitrary column/constraint.

In Rails 3 w/ActiveRecord Query Interface

l = Location.where(["id = ?", id]).select("name, website, city").first

Ref: Active Record Query Interface

You can also swap the order of these chained calls, doing .select(...).where(...).first - all these calls do is construct the SQL query and then send it off.

In rails, how to select one specific column's data from a table? (there is only 1 row so I want only a specific result but not an array)

Since there is guaranteed to be only one row, you can grab it directly via .first or .last. While you may wish to limit the selected column only to the desired breakfast with the .select() method, it probably isn't necessary and you can just retrieve breakfast from the resultant object:

Plan.last.breakfast
=> 100
# Generates this query:
Plan Load (0.4ms)  SELECT "plans".* FROM "plans" ORDER BY "plans"."id" DESC LIMIT 1

Using .select() to cause the SQL query to retrieve only the breakfast column is possible, but won't give you that much benefit other than a very tiny memory increase.

Plan.select(:breakfast).last.breakfast
=> 100
# Generates this query:
Plan Load (0.4ms)  SELECT breakfast FROM "plans" ORDER BY "plans"."id" DESC LIMIT 1

Of course, you can store it to a variable, or use it right in your expression:

if Plan.last.breakfast > 90
  # whatever
end 

Retrieving only certain columns with Rails 3 where clause

results = Model.where(:lat => (south..north), :lng => (east..west)).select([:lat, :long, :id])

You'll also probably want to include the :id in that select if you want your results to behave like reasonable ActiveRecord objects.

Edit: Select takes a single arg, can be an array.

in Rails how to select additional columns from multiple tables

result = User.first.usertags.joins(:tag).select("tags.name as tag_name, tags.id, usertags.id, user.id")

result.collect{|r| r.tag_name}

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