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module ActiveRecord
# Statement cache is used to cache a single statement in order to avoid creating the AST again.
# Initializing the cache is done by passing the statement in the initialization block:
#
# cache = ActiveRecord::StatementCache.new do
# Book.where(name: "my book").limit(100)
# end
#
# The cached statement is executed by using the +execute+ method:
#
# cache.execute
#
# The relation returned by the block is cached, and for each +execute+ call the cached relation gets duped.
# Database is queried when +to_a+ is called on the relation.
class StatementCache
Substitute = Struct.new :name
class Params
def [](name); Substitute.new name; end
end
class BindMap
def initialize(bind_values)
@value_map = {}
@bind_values = bind_values
bind_values.each_with_index do |(column, value), i|
if Substitute === value
@value_map[value.name] = i
end
end
end
def bind(values)
bvs = @bind_values.map { |pair| pair.dup }
values.each { |k,v| bvs[@value_map[k]][1] = v }
bvs
end
end
def initialize(block = Proc.new)
@mutex = Mutex.new
@relation = nil
@sql = nil
@binds = nil
@block = block
@params = Params.new
end
def execute(params)
rel = relation @params
arel = rel.arel
klass = rel.klass
bv = binds rel
klass.find_by_sql sql(klass, arel, bv), bv.bind(params)
end
alias :call :execute
private
def binds(rel)
@binds || @mutex.synchronize { @binds ||= BindMap.new rel.bind_values }
end
def sql(klass, arel, bv)
@sql || @mutex.synchronize {
@sql ||= klass.connection.to_sql arel, bv
}
end
def relation(values)
@relation || @mutex.synchronize { @relation ||= @block.call(values) }
end
end
end
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