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ActiveRecord::Calculations#pluck accepts multiple columns #6500

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@jeroeningen
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@jeroeningen jeroeningen commented May 26, 2012

Rails currently supports this:
Person.pluck(:id) # SELECT people.id FROM people

I added two possibilities:
Person.pluck(:id) # SELECT people.id FROM people
Person.pluck([:id, :name]) # SELECT people.id, people.name FROM people
Person.pluck(:id, :name) # SELECT people.id, people.name FROM people

Because I made some stupid mistakes while updating my own fork of rails/rails this is a new fork and a follow up of the discussion located here: #5472

@steveklabnik
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@steveklabnik steveklabnik commented May 26, 2012

Mentioning #5472 so that GitHub links them.

column.type_cast(value)
else
column_name.collect{|c| attributes[c.to_s]}
end

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@carlosantoniodasilva

carlosantoniodasilva May 29, 2012
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Columns need to be typecasted in both scenarios, otherwise pluck would work differently when using 1 and more columns.

if column_name.size == 1 && column_name.first.is_a?(Symbol) && column_names.include?(column_name.first.to_s)
column_name = "#{table_name}.#{column_name.first}"
elsif column_name.is_a?(Array)
column_name.flatten!
end

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@carlosantoniodasilva

carlosantoniodasilva May 29, 2012
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The same check to add the table name has to happen for each column name, otherwise the method would work differently for each case.

def test_pluck_expects_a_single_selection
assert_raise(ArgumentError) { Account.pluck 'id, credit_limit' }
def test_pluck_expects_a_single_or_multiple_selection
assert_nothing_raised(ArgumentError) { Account.pluck 'id, credit_limit' }
end

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@carlosantoniodasilva

carlosantoniodasilva May 29, 2012
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There's no need to assert for nothing raised, just make sure you're getting the right response from the sql piece. Try to test some different sqls as well.

@jonleighton
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@jonleighton jonleighton commented May 31, 2012

I think we should probably have this feature as people keep asking about it. However I think we should decide between Post.pluck([:a, :b]) and Post.pluck(:a, :b) and just support one of them. I think probably the latter.

@jeroeningen
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@jeroeningen jeroeningen commented Jun 2, 2012

@carlos, you were right with your comment my mistakes. Just fixed and pushed it!

@jon In my previous pull request, several people liked it (see #5472). So IMO that's not the problem. But why do you want to support just one of the possibilities of Post.pluck([:a, :b]) and Post.pluck(:a, :b) and not both?

@carlosantoniodasilva
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@carlosantoniodasilva carlosantoniodasilva commented Jun 22, 2012

@jeroeningen I've pulled your changes and modified as per @jonleighton comments: d59b2ab. Thanks for your work on that :).

@RKushnir
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@RKushnir RKushnir commented Nov 15, 2012

How about if pluck would also account for the select arguments? So Model.select([:id, :name]).pluck would project id and name.

@carlosantoniodasilva
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@carlosantoniodasilva carlosantoniodasilva commented Nov 15, 2012

@RKushnir we've just merged a change that will ignore the select values in 3a33572. If you think it can be improved, please feel free to open a new topic in the core mailing list. Thanks.

sgerrand pushed a commit to sgerrand/rails that referenced this pull request Nov 2, 2013
Ensure it works with mix of symbols and strings, and with a select
clause possibly containing more than one column.

Also remove support for pluck with an array of columns, in favor of
passing the list of attributes:

    Model.pluck(:a, :b)

See comments: rails#6500 (comment)
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