Customising ActiveRecord's attribute formatting on inspect

We all know that you can change how a Ruby object is represented textually through the inspect method. ActiveRecord::Base provides a useful out-of-the-box implementation of inspect that allows you to see the content of all of a record's attributes:

>> Gig.last
=> #<Gig id: 123, name: "ICELAB presents Ruby: A Rock Opera in 1.9.3 Thrilli...", starts_at: "2012-03-03 09:30:00", capacity: 750, available_ticket_numbers: nil, sold_ticket_numbers: nil, created_at: "2012-01-19 06:47:02", updated_at: "2012-01-19 06:47:02">

What you might not know is that ActiveRecord provides a hook for you to customise how each of these attributes is formatted in this inspect output. Let's see how it is used in ActiveRecord::Base#inspect:

# Returns the contents of the record as a nicely formatted string.
def inspect
  attributes_as_nice_string = self.class.column_names.collect { |name|
    if has_attribute?(name) || new_record?
      "#{name}: #{attribute_for_inspect(name)}"
    end
  }.compact.join(", ")
  "#<#{self.class} #{attributes_as_nice_string}>"
end

You'll see that it iterates over each of the attributes and passes them through attribute_for_inspect(name). This is also a public method that truncates a string if it is longer than 50 characters, shows dates in their DB-native UTC format, the otherwise just calls inspect on whatever the attribute value is.

Why would you want to customise this? We have an ActiveRecord with a few columns where we are serializing large arrays to the database

class Gig < ActiveRecord::Base
  serialize :available_ticket_numbers
  serialize :sold_ticket_numbers
end

This can lead to some very messy console output:

>> Gig.last
=> #<Gig id: 123, name: "ICELAB presents Ruby: A Rock Opera in 1.9.3 Thrilli...", starts_at: "2012-03-03 09:30:00", capacity: 750, available_ticket_numbers: nil, sold_ticket_numbers: ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "100", "101", "102", "103", "104", "105", "106", "107", "108", "109", "110", "111", "112", "113", "114", "115", "116", "117", "118", "119", "120", "121", "122", "123", "124", "125", "126", "127", "128", "129", "130", "131", "132", "133", "134", "135", "136", "137", "138", "139", "140", "141", "142", "143", "144", "145", "146", "147", "148", "149", "150", "151", "152", "153", "154", "155", "156", "157", "158", "159", "160", "161", "162", "163", "164", "165", "166", "167", "168", "169", "170", "171", "172", "173", "174", "175", "176", "177", "178", "179", "180", "181", "182", "183", "184", "185", "186", "187", "188", "189", "190", "191", "192", "193", "194", "195", "196", "197", "198", "199", "200", "201", "202", "203", "204", "205", "206", "207", "208", "209", "210", "211", "212", "213", "214", "215", "216", "217", "218", "219", "220", "221", "222", "223", "224", "225", "226", "227", "228", "229", "230", "231", "232", "233", "234", "235", "236", "237", "238", "239", "240", "241", "242", "243", "244", "245", "246", "247", "248", "249", "250", "251", "252", "253", "254", "255", "256", "257", "258", "259", "260", "261", "262", "263", "264", "265", "266", "267", "268", "269", "270", "271", "272", "273", "274", "275", "276", "277", "278", "279", "280", "281", "282", "283", "284", "285", "286", "287", "288", "289", "290", "291", "292", "293", "294", "295", "296", "297", "298", "299", "300", "301", "302", "303", "304", "305", "306", "307", "308", "309", "310", "311", "312", "313", "314", "315", "316", "317", "318", "319", "320", "321", "322", "323", "324", "325", "326", "327", "328", "329", "330", "331", "332", "333", "334", "335", "336", "337", "338", "339", "340", "341", "342", "343", "344", "345", "346", "347", "348", "349", "350", "351", "352", "353", "354", "355", "356", "357", "358", "359", "360", "361", "362", "363", "364", "365", "366", "367", "368", "369", "370", "371", "372", "373", "374", "375", "376", "377", "378", "379", "380", "381", "382", "383", "384", "385", "386", "387", "388", "389", "390", "391", "392", "393", "394", "395", "396", "397", "398", "399", "400", "401", "402", "403", "404", "405", "406", "407", "408", "409", "410", "411", "412", "413", "414", "415", "416", "417", "418", "419", "420", "421", "422", "423", "424", "425", "426", "427", "428", "429", "430", "431", "432", "433", "434", "435", "436", "437", "438", "439", "440", "441", "442", "443", "444", "445", "446", "447", "448", "449", "450", "451", "452", "453", "454", "455", "456", "457", "458", "459", "460", "461", "462", "463", "464", "465", "466", "467", "468", "469", "470", "471", "472", "473", "474", "475", "476", "477", "478", "479", "480", "481", "482", "483", "484", "485", "486", "487", "488", "489", "490", "491", "492", "493", "494", "495", "496", "497", "498", "499", "500", "501", "502", "503", "504", "505", "506", "507", "508", "509", "510", "511", "512", "513", "514", "515", "516", "517", "518", "519", "520", "521", "522", "523", "524", "525", "526", "527", "528", "529", "530", "531", "532", "533", "534", "535", "536", "537", "538", "539", "540", "541", "542", "543", "544", "545", "546", "547", "548", "549", "550", "551", "552", "553", "554", "555", "556", "557", "558", "559", "560", "561", "562", "563", "564", "565", "566", "567", "568", "569", "570", "571", "572", "573", "574", "575", "576", "577", "578", "579", "580", "581", "582", "583", "584", "585", "586", "587", "588", "589", "590", "591", "592", "593", "594", "595", "596", "597", "598", "599", "600", "601", "602", "603", "604", "605", "606", "607", "608", "609", "610", "611", "612", "613", "614", "615", "616", "617", "618", "619", "620", "621", "622", "623", "624", "625", "626", "627", "628", "629", "630", "631", "632", "633", "634", "635", "636", "637", "638", "639", "640", "641", "642", "643", "644", "645", "646", "647", "648", "649", "650", "651", "652", "653", "654", "655", "656", "657", "658", "659", "660", "661", "662", "663", "664", "665", "666", "667", "668", "669", "670", "671", "672", "673", "674", "675", "676", "677", "678", "679", "680", "681", "682", "683", "684", "685", "686", "687", "688", "689", "690", "691", "692", "693", "694", "695", "696", "697", "698", "699", "700", "701", "702", "703", "704", "705", "706", "707", "708", "709", "710", "711", "712", "713", "714", "715", "716", "717", "718", "719", "720", "721", "722", "723", "724", "725", "726", "727", "728", "729", "730", "731", "732", "733", "734", "735", "736", "737", "738", "739", "740", "741", "742", "743", "744", "745", "746", "747", "748", "749", "750", created_at: "2012-01-19 06:47:02", updated_at: "2012-01-19 06:47:02">

That's a lot of noise. Most of the time, it just gets in the way when we're trying to work with our records. If we ever wanted to inspect the content of such an attribute, we could just address it directly.

To clean this up in one shot across our entire application, we can override attribute_for_inspect. Put this in a file in lib/ somwhere and require it from your config/application.rb:

module ActiveRecord
  class Base
    alias_method :attribute_for_inspect_before_extension, :attribute_for_inspect
    def attribute_for_inspect(attr_name)
      value = read_attribute(attr_name)

      if value.kind_of?(Array) && value.length > 4
        (value[0..1] + ["... #{value.length - 4} elements ..."] + value[-2..-1]).inspect
      else
        attribute_for_inspect_before_extension(attr_name)
      end
    end
  end
end

This checks for any array attributes and gives them a shortened output if they contain more than five elements:

>> Gig.last
=> #<Gig id: 123, name: "ICELAB presents Ruby: A Rock Opera in 1.9.3 Thrilli...", starts_at: "2012-03-03 09:30:00", capacity: 750, available_ticket_numbers: nil, sold_ticket_numbers: ["1", "2", "... 746 elements ...", "749", "750"], created_at: "2012-01-19 06:47:02", updated_at: "2012-01-19 06:47:02">

Much neater. We get tidier inspect output without having to override ActiveRecord's otherwise useful inspect altogether. Depending on your app, I'd imagine you could extend it in many different ways to clean up your time on the console.