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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 create block:
#
# cache = StatementCache.create(Book.connection) do |params|
# Book.where(name: "my book").where("author_id > 3")
# end
#
# The cached statement is executed by using the
# [connection.execute]{rdoc-ref:ConnectionAdapters::DatabaseStatements#execute} method:
#
# cache.execute([], Book, Book.connection)
#
# The relation returned by the block is cached, and for each
# [execute]{rdoc-ref:ConnectionAdapters::DatabaseStatements#execute}
# call the cached relation gets duped. Database is queried when +to_a+ is called on the relation.
#
# If you want to cache the statement without the values you can use the +bind+ method of the
# block parameter.
#
# cache = StatementCache.create(Book.connection) do |params|
# Book.where(name: params.bind)
# end
#
# And pass the bind values as the first argument of +execute+ call.
#
# cache.execute(["my book"], Book, Book.connection)
class StatementCache # :nodoc:
class Substitute; end # :nodoc:
class Query # :nodoc:
def initialize(sql)
@sql = sql
end
def sql_for(binds, connection)
@sql
end
end
class PartialQuery < Query # :nodoc:
def initialize values
@values = values
@indexes = values.each_with_index.find_all { |thing,i|
Arel::Nodes::BindParam === thing
}.map(&:last)
end
def sql_for(binds, connection)
val = @values.dup
binds = connection.prepare_binds_for_database(binds)
@indexes.each { |i| val[i] = connection.quote(binds.shift) }
val.join
end
end
def self.query(visitor, ast)
Query.new visitor.accept(ast, Arel::Collectors::SQLString.new).value
end
def self.partial_query(visitor, ast, collector)
collected = visitor.accept(ast, collector).value
PartialQuery.new collected
end
class Params # :nodoc:
def bind; Substitute.new; end
end
class BindMap # :nodoc:
def initialize(bound_attributes)
@indexes = []
@bound_attributes = bound_attributes
bound_attributes.each_with_index do |attr, i|
if Substitute === attr.value
@indexes << i
end
end
end
def bind(values)
bas = @bound_attributes.dup
@indexes.each_with_index { |offset,i| bas[offset] = bas[offset].with_cast_value(values[i]) }
bas
end
end
attr_reader :bind_map, :query_builder
def self.create(connection, block = Proc.new)
relation = block.call Params.new
bind_map = BindMap.new relation.bound_attributes
query_builder = connection.cacheable_query relation.arel
new query_builder, bind_map
end
def initialize(query_builder, bind_map)
@query_builder = query_builder
@bind_map = bind_map
end
def execute(params, klass, connection)
bind_values = bind_map.bind params
sql = query_builder.sql_for bind_values, connection
klass.find_by_sql sql, bind_values
end
alias :call :execute
end
end
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