Notes posted to Ruby on Rails

Redirect to subdomain

If you’re looking to redirect to a subdomain you can do things like this:

redirect_to users_url(1, params: {a: :b}, subdomain: 'bob')

Why is this deprecated?

Anyone knows?

prepend_before_filter

If you need the method to be called at *the beginning* of the before_filter chain then you should use:

prepend_before_filter

Poor man's maybe

After creating a simple Maybe monad in Ruby, a colleaque noticed I could have just used try (I wasn’t aware try supports blocks). I think the method was even meant for such cases.

Why I mention this? Because it clarifies the whole ‘raises exception if method does not exist’ thing. It should not be crappy solution to exception handling, but allow for doing away with messy if statements. An example:

report = params[:query_type]
.try { |qt| build_query(qt) }
.try { |sql| run_query(sql) }
.try { |res| format_result(res) }

If any of the expressions params[], build_query, run_query etc. returns nil, the chain is halted and nil is returned. It still throws exceptions if a values is not nil and method does not exist, which is just like it should.

Be careful with cycles

This simplistic implementation (unlike Marshal.load(Marshal.dump(object)) doesn’t handle cycles in objects.

a = {}
b = {a: a}
a[:b] = b
a.deep_dup # SystemStackError: stack level too deep

An article about token-based authentication

www.codeschool.com/blog/2014/02/03/token-based-authentication-rails/

Have submit_tag send value as a nested resource

To have the submit_tag send it’s value within a nested resource for strong params use the name paramter.

submit_tag("Send", name: 'article[submit]')

Text improvement

Where it says: without loading a bunch of records should say: without loading a bunch of columns/attributes Considering that record usually is a row.

SQL Injection?

Note that the version of leente and timdorr are probably vulnerable to SQL Injection (through attribute param).

Probably you want to look into with_lock instead of handcrafting SQL.

arguments do not need to be an array

it’s a small point, but if you look at the source, the method is defined with the splat operator in the arguments:

def select (*fields)

this means that a list of arguments is automatically converted to an array. There is no typo in the description above.

It will also work to pass an array:

select([:field1, :field2])

although the select method interprets this as a single argument, and places it into an array (due to the splat operator), this is then passed to the _select(*fields) method, which immediately calls fields.flatten!

So either a list or an array may be passed, both will work.

How safe is this?

Could this be used against a user supplied fragment like in a url route ?

Rails 3.2 / 4.x with_scope replacement

If you’re looking for with_scope replacement for newer versions, see http://apidock.com/rails/ActiveRecord/Relation/scoping

Group method chain

The group_method parameter can be a string representing a method chain:

grouped_collection_select(:city, :country_id, @continents, 'countries.sort.reverse', :name, :id, :name)

If we were to modify the Country model so we can sort by name:

class Country
  include Comparable

  def <=>(other)
    self.name <=> other.name
  end
end

The above example would have given us the countries sorted by name in descending sequence.

'max-stale' should be sent by client, not by server

3rd example is a trap.

Adding index with other operator classes (PostgreSQL)

To perform on search by LIKE:

SQL Query:

SELECT users.* FROM users WHERE name LIKE 'Doug%';

Explain:

# Without index
Seq Scan on users  (cost=0.00..82183.32 rows=98524 width=418)
  Filter: ((name)::text ~~ 'Doug%'::text)

Adding index with operator class ‘varchar_pattern_ops’

add_index :users, :name, order: {name: :varchar_pattern_ops}
execute 'ANALYZE users;'

New Explain:

# With index
Bitmap Heap Scan on users  (cost=2444.46..56020.97 rows=98524 width=418)
  Filter: ((name)::text ~~ 'Doug%'::text)
  ->  Bitmap Index Scan on index_users_on_name  (cost=0.00..2419.83 rows=75940 width=0)
        Index Cond: ((name)::text ~>=~ 'Doug'::text)

Arguments for .select must be array

Model.select(:field, :other_field, :and_one_more) has a typo. It must take an array of arguments as the description states:

Model.select([:field, :other_field, :and_one_more])

Also useful without respond_with

Using the class method #respond_to allows controller-level specification of the allowed mime-types. Without #respond_with , it enables a

Completed 406 Not Acceptable

response rather than

ActionView::MissingTemplate

error when an unsupported type is requested.

See: http://www.justinweiss.com/blog/2014/11/03/respond-to-without-all-the-pain/

Bangladeshi Taka (BDT 1,200.95)

Code example

def to_bdt(amount)
  number_to_currency(amount, :unit => "BDT ", :separator => ".", :delimiter => ",")
end

Include items affected in output

If the result returned from the block is an Integer, the output will include a message about that number of “rows” in addition to the elapsed time.

say_with_time "Some complex, custom work" do
  counter = 0
  # ... do some stuff here that increments the counter ...
  counter
end

#=> "-- Some complex, custom work"
#=> "   -> 45.3725s"
#=> "   -> 52880 rows"

Include items affected in output

If the result returned from the block is an Integer, the output will include a message about that number of “rows” in addition to the elapsed time.

say_with_time "Some complex, custom work" do
  counter = 0
  # ... do some stuff here that increments the counter ...
  counter
end

#=> "-- Some complex, custom work"
#=> "   -> 45.3725s"
#=> "   -> 52880 rows"

Opposite of persisted?

So I can find it when I look next time.

Opposite of #new_record?

So that next time I look I find it.

Non Layout Pages

A 404 error for the favicon will be thrown on pages where there is no layout if there isn’t a favicon in the public folder.

A situation would be when a controller method is used to render an image and the user chooses to open the image in a new tab bypassing the layout and the favicon_link_tag.

Find the First Instance in the Table. If None Exists, Create One.

Specify the data you’re looking for. If it exists in the table, the first instance will be returned. If not, then create is called.

If a block is provided, that block will be executed only if a new instance is being created. The block is NOT executed on an existing record.

Code example

MyStat.where(name: statistic_name).first_or_create do |statistic|
  statistic.value = calculate_percentage
  statistic.statistic_type = "percentage"
end

Order with hash parameters only in ActiveRecord >= 4.0

If you use order with hash parameters on AR3 versions it wont work.

Visually Explained

http://degenportnoy.blogspot.in/2010/05/rails-aliasmethodchain-explained-with.html

facing issue in create table (errno: 150)

I am trying to create table by writing the following code:

create_table :sam_server_user_audit do | t | t.column :user_id, :string, :limit => 100, :null => false t.column :user_type, :string, :limit => 20, :null => false t.column :status, :string, :limit => 20, :null => false t.column :created_at, :datetime, :null => false end

which generates:

CREATE TABLE `sam_server_user_audit` (`id` int(11) DEFAULT NULL auto_increment PRIMARY KEY, `user_id` varchar(100) NOT NULL, `user_type` varchar(20) NOT NULL, `status` varchar(20) NOT NULL, `created_at` datetime NOT NULL, FOREIGN KEY (user_id) REFERENCES users (id)) ENGINE=InnoDB CHARACTER SET `utf8`

here It is adding a foreign key user_id automatically.

How can I avoid that?

Ordering on associations

For ordering on the attribute of an associated model you have to include it:

Package.includes(:package_size).order("package_sizes.sort_order")

Preselecting options

To preselect options, pass in the selected options in the options hash:

{ :selected => [ selected_option_1, selected__option_2, ... ] }

Code example

grouped_collection_select(:city, :country_id, @continents, :countries, :name, :id, :name, { :selected => [1, 5, 6 ] } )

correct link below

http://apidock.com/rails/ActiveSupport/Inflector/demodulize