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  • Fetching records in batches in rails

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    Hi Friends,
    Many times we get into a situation where we have to fetch a large record from a table and need to iterate over it and that makes our server cry. As it consumes a lots a memory and time. So no need to worry again for that Rails has a solution to retrieve records in batches, There are two methods given in Rails for retrieving records in batches:

    (a)find_each
    (b)find_in_batches

    (a)find_each: It makes looping over a collection of Active record objects much cheaper by performing a batch retrieval of the database records and caching them. So the process runs in batches and you can specify batch sizes of your own.

    Example:

    Blog.find_each do |blog|
      export_to_csv(blog.user.email)
    end
    

    It also allows all the methods of find except order and limit.Some optional methods are:

    begin_at: It allows you to configure the first ID of the sequence.
    batch_size: It specifies the number of records to be fetched in each batch.
    end_at: It is similar to begin_at, but it specifies the last ID of the sequence.

    An example containing all the options is:
    Blog.find_each(begin_at: 100, end_at: 500, batch_size: 50) do |blog|
      export_to_csv(blog.user.email)
    end
    


    (b)find_in_batches: It is similar to find_each, the difference is that it takes batches to the block as an array of models, in place of taking them individually.
    Example:

    #Export CSV of emails of bloggers 150 at each time
    Blog.find_in_batches do |blogs|
      fetch_emails_and_export_to_csv(blogs)
    end
    


    Hope you liked this blogs. For more blogs go to my profile

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