How to add conditional where clauses in rails

问题

I am a rails newbie and am trying to perform a search on a table with rails, and i'm just using my sql knowledge to do this. But this just doesn't seems like rails or ruby even...

Is there any better way to do what i'm doing below? (basically, only pass date arguments to sql if they are filled)

def search(begin_date=nil, end_date=nil)

    subject = " and created_at "

    if !(begin_date.nil? || end_date.nil?)
      where_part = subject + "BETWEEN :begin_date AND :end_date"
    else if (begin_date.nil? && end_date.nil?) 
      where_part = ""
    else if(begin_date.nil?)
      where_part = subject + " <= :end_date"
    else if (end_date.nil?)
      where_part = subject + " >= :begin_date"
    end
    end
    end
    end

    User.joins(places: {containers: {label: :user}}).where("users.id= :user_id "+where_part, user_id: self.id, begin_date:begin_date, end_date:end_date).group(...).select(...)
end

EDIT

user.rb

has_many :containers
has_many :user_places
has_many :places, through: :user_places
has_many :labels

place.rb

has_many :containers
has_many :user_places
has_many :users, through: :user_places

container.rb

belongs_to :label
belongs_to :place
belongs_to :user

label.rb

belongs_to :user
has_many :containers

Basically, i want to get a count of the number of containers within a given user's labels or with a direct relationship, per location, and want to be able to filter it by begin and end dates.

Either of this dates may be nil, and so i would need to address this in my "query".

My question is : How can i do this the rails way? I took a look at http://guides.rubyonrails.org/active_record_querying.html and perhaps i could use the except command here somewhere...but this relationship model just seems a bit complex to do this with ActiveRecord...how may I?, i really think i should use ActiveRecord, but how?

Thank you

回答1:

You can apply multiple where calls to a query so you can build your base query:

query = User.joins(...)
            .group(...)
            .select(...)
            .where('users.id = :user_id', :user_id => self.id)

and then add another where call depending on your date interval:

if(begin_date && end_date)
  query = query.where(:created_at => begin_date .. end_date)
  # or where('created_at between :begin_date and :end_date', :begin_date => begin_date, :end_date => end_date)
elsif(begin_date)
  query = query.where('created_at >= :begin_date', :begin_date => begin_date)
elsif(end_date)
  query = query.where('created_at <= :end_date', :end_date => end_date)
end

Each where call adds another piece to your overall WHERE clause using AND so something like:

q = M.where(a).where(b).where(c)

is the same as saying WHERE a AND b AND c.

回答2:

I cant think of a great reason why you would actually want to generate SQL in your code. Active record seems like a much more efficient solution for your needs, unless there is a reason why you cant use that.

Link explaining how to join tables with active record

来源：https://stackoverflow.com/questions/11689720/how-to-add-conditional-where-clauses-in-rails

标签

sql

ruby-on-rails

ruby

conditional

rails-activerecord