1 files changed, 132 insertions, 0 deletions
diff --git a/config/initializers/postgresql_cte.rb b/config/initializers/postgresql_cte.rb
new file mode 100644
index 00000000000..7f0df8949db
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+++ b/config/initializers/postgresql_cte.rb
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+# Adds support for WITH statements when using PostgreSQL. The code here is taken
+# from https://github.com/shmay/ctes_in_my_pg which at the time of writing has
+# not been pushed to RubyGems. The license of this repository is as follows:
+#
+# The MIT License (MIT)
+#
+# Copyright (c) 2012 Dan McClain
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+module ActiveRecord
+  class Relation
+    class Merger # :nodoc:
+      def normal_values
+        NORMAL_VALUES + [:with]
+      end
+    end
+  end
+end
+
+module ActiveRecord::Querying
+  delegate :with, to: :all
+end
+
+module ActiveRecord
+  class Relation
+    # WithChain objects act as placeholder for queries in which #with does not have any parameter.
+    # In this case, #with must be chained with #recursive to return a new relation.
+    class WithChain
+      def initialize(scope)
+        @scope = scope
+      end
+
+      # Returns a new relation expressing WITH RECURSIVE
+      def recursive(*args)
+        @scope.with_values += args
+        @scope.recursive_value = true
+        @scope
+      end
+    end
+
+    def with_values
+      @values[:with] || []
+    end
+
+    def with_values=(values)
+      raise ImmutableRelation if @loaded
+      @values[:with] = values
+    end
+
+    def recursive_value=(value)
+      raise ImmutableRelation if @loaded
+      @values[:recursive] = value
+    end
+
+    def recursive_value
+      @values[:recursive]
+    end
+
+    def with(opts = :chain, *rest)
+      if opts == :chain
+        WithChain.new(spawn)
+      elsif opts.blank?
+        self
+      else
+        spawn.with!(opts, *rest)
+      end
+    end
+
+    def with!(opts = :chain, *rest) # :nodoc:
+      if opts == :chain
+        WithChain.new(self)
+      else
+        self.with_values += [opts] + rest
+        self
+      end
+    end
+
+    def build_arel
+      arel = super()
+
+      build_with(arel) if @values[:with]
+
+      arel
+    end
+
+    def build_with(arel)
+      with_statements = with_values.flat_map do |with_value|
+        case with_value
+        when String
+          with_value
+        when Hash
+          with_value.map  do |name, expression|
+            case expression
+            when String
+              select = Arel::Nodes::SqlLiteral.new "(#{expression})"
+            when ActiveRecord::Relation, Arel::SelectManager
+              select = Arel::Nodes::SqlLiteral.new "(#{expression.to_sql})"
+            end
+            Arel::Nodes::As.new Arel::Nodes::SqlLiteral.new("\"#{name}\""), select
+          end
+        when Arel::Nodes::As
+          with_value
+        end
+      end
+
+      unless with_statements.empty?
+        if recursive_value
+          arel.with :recursive, with_statements
+        else
+          arel.with with_statements
+        end
+      end
+    end
+  end
+end