Created
May 22, 2012 07:36
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Nested Hash with Database
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module MockRetriever | |
def self.fetch_rows database, table | |
return ["#{rand(100)} Main St.", "#{rand(100)} Second Ave.", "#{rand(100)} Peach Ln."] | |
end | |
end | |
module AddressHandler | |
# @addresses = Hash.new( {} ) # old code - returns the SAME hash, not a new hash | |
@addresses = Hash.new { |hash, key| hash[key] = {} } | |
def self.addresses state, city | |
if value = @addresses[state][city] | |
puts "fetched stored value" | |
value | |
else | |
puts "storing new value" | |
@addresses[state][city] = MockRetriever.fetch_rows state, city | |
end | |
end | |
end | |
if __FILE__ == $0 | |
p AddressHandler.addresses 'alaska', 'anchorage' | |
p AddressHandler.addresses 'washington', 'vancouver' | |
p AddressHandler.addresses 'british columbia', 'vancouver' | |
p AddressHandler.addresses 'washington', 'vancouver' | |
end |
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With @addresses = Hash.new( {} ):
storing new value
["7 Main St.", "48 Second Ave.", "31 Peach Ln."]
storing new value
["98 Main St.", "87 Second Ave.", "39 Peach Ln."]
fetched stored value
["98 Main St.", "87 Second Ave.", "39 Peach Ln."]
fetched stored value
["98 Main St.", "87 Second Ave.", "39 Peach Ln."]
With @addresses = Hash.new { |hash, key| hash[key] = {} }
storing new value
["67 Main St.", "76 Second Ave.", "76 Peach Ln."]
storing new value
["67 Main St.", "8 Second Ave.", "8 Peach Ln."]
storing new value
["98 Main St.", "55 Second Ave.", "98 Peach Ln."]
fetched stored value
["67 Main St.", "8 Second Ave.", "8 Peach Ln."]
The latter is the desired behavior.