Add ability to concatenate Arel.sql fragments

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Multiple `Arel::Nodes::SqlLiteral` nodes can now be added together to
+    form `Arel::Nodes::Fragments` nodes. This allows joining several pieces
+    of SQL.
+
+    *Matthew Draper*, *Ole Friis*
+
 *   `ActiveRecord::Base#signed_id` raises if called on a new record
 
     Previously it would return an ID that was not usable, since it was based on `id = nil`.

activerecord/lib/arel/nodes.rb

@@ -8,6 +8,7 @@
 require "arel/nodes/insert_statement"
 require "arel/nodes/update_statement"
 require "arel/nodes/bind_param"
+require "arel/nodes/fragments"
 
 # terminal
 

activerecord/lib/arel/nodes/fragments.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Fragments < Arel::Nodes::Node
+      attr_reader :values
+
+      def initialize(values = [])
+        super()
+        @values = values
+      end
+
+      def initialize_copy(other)
+        super
+        @values = @values.clone
+      end
+
+      def hash
+        [@values].hash
+      end
+
+      def +(other)
+        raise ArgumentError, "Expected Arel node" unless Arel.arel_node?(other)
+
+        self.class.new([*@values, other])
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.values == other.values
+      end
+      alias :== :eql?
+    end
+  end
+end

activerecord/lib/arel/nodes/sql_literal.rb

@@ -14,6 +14,12 @@ def encode_with(coder)
 
       def fetch_attribute
       end
+
+      def +(other)
+        raise ArgumentError, "Expected Arel node" unless Arel.arel_node?(other)
+
+        Fragments.new([self, other])
+      end
     end
   end
 end

activerecord/lib/arel/visitors/to_sql.rb

@@ -791,6 +791,10 @@ def visit_Array(o, collector)
         end
         alias :visit_Set :visit_Array
 
+        def visit_Arel_Nodes_Fragments(o, collector)
+          inject_join o.values, collector, " "
+        end
+
         def quote(value)
           return value if Arel::Nodes::SqlLiteral === value
           @connection.quote value

activerecord/test/cases/arel/nodes/fragments_test.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+require "yaml"
+
+module Arel
+  module Nodes
+    class FragmentsTest < Arel::Spec
+      describe "equality" do
+        it "is equal with equal values" do
+          array = [Fragments.new(["foo", "bar"]), Fragments.new(["foo", "bar"])]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different values" do
+          array = [Fragments.new(["foo"]), Fragments.new(["bar"])]
+          assert_equal 2, array.uniq.size
+        end
+
+        it "can be joined with other nodes" do
+          fragments = Fragments.new(["foo", "bar"])
+          sql = Arel.sql("SELECT")
+          joined_fragments = fragments + sql
+
+          assert_equal ["foo", "bar"], fragments.values
+          assert_equal ["foo", "bar", sql], joined_fragments.values
+        end
+
+        it "fails if joined with something that is not an Arel node" do
+          fragments = Fragments.new
+          assert_raises ArgumentError do
+            fragments + "Not a node"
+          end
+        end
+      end
+    end
+  end
+end

activerecord/test/cases/arel/nodes/sql_literal_test.rb

@@ -70,6 +70,23 @@ def compile(node)
           assert_equal("foo", YAML.load(yaml_literal))
         end
       end
+
+      describe "addition" do
+        it "generates a Fragments node" do
+          sql1 = Arel.sql "SELECT *"
+          sql2 = Arel.sql "FROM users"
+          fragments = sql1 + sql2
+          _(fragments).must_be_kind_of Arel::Nodes::Fragments
+          assert_equal([sql1, sql2], fragments.values)
+        end
+
+        it "fails if joined with something that is not an Arel node" do
+          sql = Arel.sql "SELECT *"
+          assert_raises ArgumentError do
+            sql + "Not a node"
+          end
+        end
+      end
     end
   end
 end

activerecord/test/cases/arel/visitors/to_sql_test.rb

@@ -768,6 +768,20 @@ def dispatch
           }
         end
       end
+
+      describe "Nodes::Fragments" do
+        it "joins subexpressions" do
+          sql = Arel.sql("SELECT foo, bar") + Arel.sql(" FROM customers")
+          _(compile(sql)).must_be_like "SELECT foo, bar FROM customers"
+        end
+
+        it "can be built by adding SQL fragments one at a time" do
+          sql = Arel.sql("SELECT foo, bar")
+          sql += Arel.sql("FROM customers")
+          sql += Arel.sql("GROUP BY foo")
+          _(compile(sql)).must_be_like "SELECT foo, bar FROM customers GROUP BY foo"
+        end
+      end
     end
   end
 end