Class: NcsNavigator::Warehouse::Filters::CompositeFilter

Inherits:
Object
  • Object
show all
Extended by:
Forwardable
Includes:
Enumerable
Defined in:
lib/ncs_navigator/warehouse/filters/composite_filter.rb

Overview

Encapsulates an ordered list of filters that can be applied to one or more records. Filters of this type are used in EnumTransformer and Contents.

Each filter is an object with an call method. The call method takes an array of zero or more records as input and returns an array of zero or more records. The input and output arrays may be the same or different. A filter may add, remove, or mutate records (or all three).

A filter will be called multiple times for a single transform run, but it will never see the same record twice. To put it another way, the first filter will be invoked exactly once per record yielded from the underlying enumeration. Subsequent filters are invoked on the return value from the previous filter.

Depending on the filter order, a particular filter may never see some of the eventually transformed records. This will happen if records are created by a filter lower in the filter chain.

Leaky abstraction note: if a filter needs to change the primary key for a record, there is unfortunate DataMapper behavior to contend with. DM memoizes the result of Resource#key after the first time it is invoked. The warehouse infrastructure will certainly have invoked #key on a record which is passed to a filter's call method. In order so that subsequent calls to #key reflect the filter's changes, it needs to work around this. Two possibilities:

  • Instead of changing the key on the passed-in record, create a new record with the new key (and all the other attributes) and return that.
  • record.instance_eval { remove_instance_variable(:@_key) }

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(filter_objects) ⇒ CompositeFilter

Returns a new instance of CompositeFilter.



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# File 'lib/ncs_navigator/warehouse/filters/composite_filter.rb', line 42

def initialize(filter_objects)
  check_filters(filter_objects)

  @filters = filter_objects
end

Instance Attribute Details

#filters ⇒ Object

Returns the value of attribute filters.



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# File 'lib/ncs_navigator/warehouse/filters/composite_filter.rb', line 40

def filters
  @filters
end

Instance Method Details

#call(records) ⇒ Array

Returns the filtered records.

Parameters:

  • records (Array) —

    zero or more records to filter.

Returns:

  • (Array) —

    the filtered records.



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# File 'lib/ncs_navigator/warehouse/filters/composite_filter.rb', line 51

def call(records)
  filters.inject(ensure_array(records)) { |result, filter| ensure_array(filter.call(result)) }
end