Php – Step by step migration from Zend Framework 1 to 2

There are different ways to delete an array element, where some are more useful for some specific tasks than others.

Deleting a single array element

If you want to delete just one array element you can use unset() or alternatively \array_splice().

If you know the value and don’t know the key to delete the element you can use \array_search() to get the key. This only works if the element does not occur more than once, since \array_search returns the first hit only.

unset()

Note that when you use unset() the array keys won’t change. If you want to reindex the keys you can use \array_values() after unset(), which will convert all keys to numerically enumerated keys starting from 0.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];
unset($array[1]);
          // ↑ Key which you want to delete

Output:

[
    [0] => a
    [2] => c
]

\array_splice() method

If you use \array_splice() the keys will automatically be reindexed, but the associative keys won’t change — as opposed to \array_values(), which will convert all keys to numerical keys.

\array_splice() needs the offset, not the key, as the second parameter.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];
\array_splice($array, 1, 1);
                   // ↑ Offset which you want to delete

Output:

[
    [0] => a
    [1] => c
]

array_splice(), same as unset(), take the array by reference. You don’t assign the return values of those functions back to the array.

Deleting multiple array elements

If you want to delete multiple array elements and don’t want to call unset() or \array_splice() multiple times you can use the functions \array_diff() or \array_diff_key() depending on whether you know the values or the keys of the elements which you want to delete.

\array_diff() method

If you know the values of the array elements which you want to delete, then you can use \array_diff(). As before with unset() it won’t change the keys of the array.

Code:

$array = [0 => "a", 1 => "b", 2 => "c", 3 => "c"];
$array = \array_diff($array, ["a", "c"]);
                          // └────────┘
                          // Array values which you want to delete

Output:

[
    [1] => b
]

\array_diff_key() method

If you know the keys of the elements which you want to delete, then you want to use \array_diff_key(). You have to make sure you pass the keys as keys in the second parameter and not as values. Keys won’t reindex.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];
$array = \array_diff_key($array, [0 => "xy", "2" => "xy"]);
                               // ↑           ↑
                               // Array keys which you want to delete

Output:

[
    [1] => b
]

If you want to use unset() or \array_splice() to delete multiple elements with the same value you can use \array_keys() to get all the keys for a specific value and then delete all elements.

rename_column :table, :old_column, :new_column

You'll probably want to create a separate migration to do this. (Rename FixColumnName as you will.):

script/generate migration FixColumnName
# creates  db/migrate/xxxxxxxxxx_fix_column_name.rb

Then edit the migration to do your will:

# db/migrate/xxxxxxxxxx_fix_column_name.rb
class FixColumnName < ActiveRecord::Migration
  def self.up
    rename_column :table_name, :old_column, :new_column
  end

  def self.down
    # rename back if you need or do something else or do nothing
  end
end

For Rails 3.1 use:

While, the up and down methods still apply, Rails 3.1 receives a change method that "knows how to migrate your database and reverse it when the migration is rolled back without the need to write a separate down method".

See "Active Record Migrations" for more information.

rails g migration FixColumnName

class FixColumnName < ActiveRecord::Migration
  def change
    rename_column :table_name, :old_column, :new_column
  end
end

If you happen to have a whole bunch of columns to rename, or something that would have required repeating the table name over and over again:

rename_column :table_name, :old_column1, :new_column1
rename_column :table_name, :old_column2, :new_column2
...

You could use change_table to keep things a little neater:

class FixColumnNames < ActiveRecord::Migration
  def change
    change_table :table_name do |t|
      t.rename :old_column1, :new_column1
      t.rename :old_column2, :new_column2
      ...
    end
  end
end

Then just db:migrate as usual or however you go about your business.

For Rails 4:

While creating a Migration for renaming a column, Rails 4 generates a change method instead of up and down as mentioned in the above section. The generated change method is:

$ > rails g migration ChangeColumnName

which will create a migration file similar to:

class ChangeColumnName < ActiveRecord::Migration
  def change
    rename_column :table_name, :old_column, :new_column
  end
end