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Add ability to specify how a class is converted to Arel predicate

This adds the ability for rails apps or gems to have granular control
over how a domain object is converted to sql. One simple use case would
be to add support for Regexp. Another simple case would be something
like the following:

    class DateRange < Struct.new(:start, :end)
      def include?(date)
        (start..end).cover?(date)
      end
    end

    class DateRangePredicate
      def call(attribute, range)
        attribute.in(range.start..range.end)
      end
    end

    ActiveRecord::PredicateBuilder.register_handler(DateRange,
      DateRangePredicate.new)

More complex cases might include taking a currency object and converting
it from EUR to USD before performing the query.

By moving the existing handlers to this format, we were also able to
nicely refactor a rather nasty method in PredicateBuilder.
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1 parent 953b577 commit 92a603387c084f13a36bbf3844d89029bb73a753 @sgrif sgrif committed with sgrif May 17, 2013
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10 activerecord/CHANGELOG.md
@@ -1,3 +1,13 @@
+* Add ability to define how a class is converted to Arel predicates.
+ For example, adding a very vendor specific regex implementation:
+
+ regex_handler = proc do |column, value|
+ Arel::Nodes::InfixOperation.new('~', column, value.source)
+ end
+ ActiveRecord::PredicateBuilder.register_handler(Regexp, regex_handler)
+
+ *Sean Griffin & @joannecheng*
+
* Don't allow `quote_value` to be called without a column.
Some adapters require column information to do their job properly.
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67 activerecord/lib/active_record/relation/predicate_builder.rb
@@ -1,5 +1,10 @@
module ActiveRecord
class PredicateBuilder # :nodoc:
+ @handlers = []
+
+ autoload :RelationHandler, 'active_record/relation/predicate_builder/relation_handler'
+ autoload :ArrayHandler, 'active_record/relation/predicate_builder/array_handler'
+
def self.resolve_column_aliases(klass, hash)
hash = hash.dup
hash.keys.grep(Symbol) do |key|
@@ -73,44 +78,36 @@ def self.references(attributes)
end.compact
end
+ # Define how a class is converted to Arel nodes when passed to +where+.
+ # The handler can be any object that responds to +call+, and will be used
+ # for any value that +===+ the class given. For example:
+ #
+ # MyCustomDateRange = Struct.new(:start, :end)
+ # handler = proc do |column, range|
+ # Arel::Nodes::Between.new(column,
+ # Arel::Nodes::And.new([range.start, range.end])
+ # )
+ # end
+ # ActiveRecord::PredicateBuilder.register_handler(MyCustomDateRange, handler)
+ def self.register_handler(klass, handler)
+ @handlers.unshift([klass, handler])
+ end
+
+ register_handler(BasicObject, ->(attribute, value) { attribute.eq(value) })
+ # FIXME: I think we need to deprecate this behavior
+ register_handler(Class, ->(attribute, value) { attribute.eq(value.name) })
+ register_handler(Base, ->(attribute, value) { attribute.eq(value.id) })
+ register_handler(Range, ->(attribute, value) { attribute.in(value) })
+ register_handler(Relation, RelationHandler.new)
+ register_handler(Array, ArrayHandler.new)
+
private
def self.build(attribute, value)
- case value
- when Array
- values = value.to_a.map {|x| x.is_a?(Base) ? x.id : x}
- ranges, values = values.partition {|v| v.is_a?(Range)}
-
- values_predicate = if values.include?(nil)
- values = values.compact
-
- case values.length
- when 0
- attribute.eq(nil)
- when 1
- attribute.eq(values.first).or(attribute.eq(nil))
- else
- attribute.in(values).or(attribute.eq(nil))
- end
- else
- attribute.in(values)
- end
+ handler_for(value).call(attribute, value)
+ end
- array_predicates = ranges.map { |range| attribute.in(range) }
- array_predicates << values_predicate
- array_predicates.inject { |composite, predicate| composite.or(predicate) }
- when ActiveRecord::Relation
- value = value.select(value.klass.arel_table[value.klass.primary_key]) if value.select_values.empty?
- attribute.in(value.arel.ast)
- when Range
- attribute.in(value)
- when ActiveRecord::Base
- attribute.eq(value.id)
- when Class
- # FIXME: I think we need to deprecate this behavior
- attribute.eq(value.name)
- else
- attribute.eq(value)
- end
+ def self.handler_for(object)
+ @handlers.detect { |klass, _| klass === object }.last
end
end
end
View
29 activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
@@ -0,0 +1,29 @@
+module ActiveRecord
+ class PredicateBuilder
+ class ArrayHandler # :nodoc:
+ def call(attribute, value)
+ values = value.map { |x| x.is_a?(Base) ? x.id : x }
+ ranges, values = values.partition { |v| v.is_a?(Range) }
+
+ values_predicate = if values.include?(nil)
+ values = values.compact
+
+ case values.length
+ when 0
+ attribute.eq(nil)
+ when 1
+ attribute.eq(values.first).or(attribute.eq(nil))
+ else
+ attribute.in(values).or(attribute.eq(nil))
+ end
+ else
+ attribute.in(values)
+ end
+
+ array_predicates = ranges.map { |range| attribute.in(range) }
+ array_predicates << values_predicate
+ array_predicates.inject { |composite, predicate| composite.or(predicate) }
+ end
+ end
+ end
+end
View
13 activerecord/lib/active_record/relation/predicate_builder/relation_handler.rb
@@ -0,0 +1,13 @@
+module ActiveRecord
+ class PredicateBuilder
+ class RelationHandler # :nodoc:
+ def call(attribute, value)
+ if value.select_values.empty?
+ value = value.select(value.klass.arel_table[value.klass.primary_key])
+ end
+
+ attribute.in(value.arel.ast)
+ end
+ end
+ end
+end
View
14 activerecord/test/cases/relation/predicate_builder_test.rb
@@ -0,0 +1,14 @@
+require "cases/helper"
+require 'models/topic'
+
+module ActiveRecord
+ class PredicateBuilderTest < ActiveRecord::TestCase
+ def test_registering_new_handlers
+ PredicateBuilder.register_handler(Regexp, proc do |column, value|
+ Arel::Nodes::InfixOperation.new('~', column, value.source)
+ end)
+
+ assert_match %r{["`]topics["`].["`]title["`] ~ 'rails'}, Topic.where(title: /rails/).to_sql
+ end
+ end
+end

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