Re: Appending to an Array

On Tue, Feb 7, 2012 at 10:27 PM, Anthony Simonelli
<[e-mail]> wrote:
> I am querying a database using DBI and ODBC. =A0After I run the execute, =
I
> want to grab each row as an array, and add it to another array, essential=
ly
> creating an Array of Arrays. =A0I've tried this two ways with the same re=
sult:
>
> sth =3D dbh.execute("SELECT * FROM SOMETABLE")
> rows =3D sth.fetch_all
>
> and
>
> rows =3D sth.fetch do |row|
> =A0 =A0rows << row
> end
>
> The result for both is that the last row is repeated in the array however
> many times there are rows. =A0Why isn't it appending correctly?

Probably because the DB driver optimizes object allocation and reuses
the same instance.  Then this is what happens:

irb(main):006:0> rows =3D []
=3D> []
irb(main):007:0> a =3D %w{a b c d}
=3D> ["a", "b", "c", "d"]
irb(main):008:0> rows << a
=3D> [["a", "b", "c", "d"]]
irb(main):009:0> a[2] =3D 99
=3D> 99
irb(main):010:0> rows << a
=3D> [["a", "b", 99, "d"], ["a", "b", 99, "d"]]

The phenomenon is called "aliasing".

You can solve it by copying row Arrays.

rows =3D []

sth.fetch do |row|
  rows << row.to_a # if rows is not an Array
  rows << row.dup # if rows is an Array
end

Kind regards

robert


--=20
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