Rails: How to Check If a Column Has a Value

Rails: How do I check if a column has a value?

This is what you asked for:

<% for agent in @broker.agents %>
  <% unless agent.cell.blank? %>
    <span class="cell-number">Cell: <%= agent.cell %></span>
  <% end %>
<% end %>

The cell? method works whether cell is nil or an empty string. Rails adds similar functions for all ActiveRecord attributes. This will look a little nicer:

<% for agent in @broker.agents %>
  <span class="cell-number">
    Cell: <%= agent.cell? ? "none given" : agent.cell %>
  </span>
<% end %>

The question mark and colon form a quick "if ? then : else" statement. There are two question marks in the code above because one is part of the method name cell? and the other is a part of the if/then/else construction.

Check whether a table column has any value

Try this in controller

@fabrics = Shirt.uniq.pluck(:fabric).reject { |f| f.nil? || f.empty? }

Rails: find if a value exists inside a array column

Discount.where(":user_id = ANY(user_id)", user_id: current_user.id)

This should do it for you. I assume that user_id is an array field in a postgres database.

I'd recommend that you also index user_id to be more performant. To create an index for your array column, you must choose between GiST and GIN as strategies. The documentation covers the options nicely, but the distilled version is that GIN lookups are much (3x) faster, but take longer (10x) to build. If your data is read far more often than it is written, go for GIN.

Your migration could be something like:

create_table "discounts", force: :cascade do |t|
  t.string "amount"
  t.string "name"
  t.string "from"
  t.string "to"
  t.integer "user_id", default: [], array: true
end

add_index  :discounts, :user_id, using: 'gin'

How to check if a column is present in a table?

You can use has_attribute?:

user = User.new
user.has_attribute?(params[:group])

How to check if a model has a certain column/attribute?

For a class

Use Class.column_names.include? attr_name where attr_name is the string name of your attribute.

In this case: Number.column_names.include? 'one'

For an instance

Use record.has_attribute?(:attr_name) or record.has_attribute?('attr_name') (Rails 3.2+) or record.attributes.has_key? attr_name.

In this case: number.has_attribute?(:one) or number.has_attribute?('one') or number.attributes.has_key? 'one'

Rails 4 detect if all the values in a column are the same

You can use uniq and pluck to do that:

puts Person.uniq.pluck(:birth_date).count == 1

You can also use select method

puts Person.select('DISTINCT birth_date').count == 1

How to check if all records of an instance have one of many values from a list of values?

Your question title does not match the description. You're not checking whether "all records have the same value", you're checking that all records have one of many values (from a list).

There are a few issues with your attempt:

self.order.items.each do |item|
  if item.state = "order_accepted" or item.state = "order_refused"
    # ...

1. Redundant use of self
2. Use of = is setting the value, rather than checking for equality. (This would be done with ==.)
3. By looping through all items like that, you're updating the order multiple times.
4. ...And since you're performing the check for each item, rather than all items, you're not checking that they all have the desired value.

A minimal change to your attempt that would work is:

if order.items.all? { |item| item.state == "order_accepted" || item.state == "order_refused" }
  order.update_attributes(treated: "true")
end

However, that's not a great solution since you're loading all objects into memory and looping through them. This is inefficient, especially if there are lots of items. A better approach is to perform the check directly in SQL rather than in ruby:

if order.items.where.not(state: ["order_accepted", "order_refused"]).empty?
  order.update_attribute(:treated, "true")
end

To tidy this code up a little, I would define that query as a scope on the Item model, such as:

class Item < ApplicationRecord
  scope :not_completed, -> { where.not(state: ["order_accepted", "order_refused"]) }
end

And then perhaps define a method on the Order model too:

class Order < ApplicationRecord
  def complete?
    items.not_completed.empty?
  end
end

Then in the code above, you can just write:

def treatment
  # ...
  order.update_attribute(:treated, "true") if order.complete?
  # ...
end

Also, I suspect that should really be true rather than "true". true is a boolean; "true" is a string. Use the correct data type for the job.

Rails may be automatically casting the value to a boolean on your behalf (?), but I would consider it bad practice to use the wrong data type, regardless.

Ruby on Rails, find if a certain value exists in a column

Try this:

if User.exists?(:email => params[:user][:email])
    flash.now[:error] = "A user with this password already exists"
    render :action => :new, :layout => 'signin-layout.html.erb'
    ...
else 
  # more code here..
end

Also, you can add validations when you're creating the object:

class User
  validates_uniqueness_of :email

More on different validations here: http://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html

Checking if a tablecolumn contains a certain value

Maybe something like this:

<% if @user.games.rounds.submitted_pictures.where(:isFinalPicture => true).any? %>

How do I check to see if a column that stores an array 'includes' a parameter passed in to a 'where'?

If you are talking about Postgresql array column, take a look at this blog post which nicely summarizes using this type of column under rails.

You should be able to find records with any matching refactor_rule with the following syntax:

Question.where("? = ANY (refactor_rules)", params[:rule])

See the ANY operator for more docs.

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