Support function table names in Arel Table

Make it possible to select from computed/function table using Arel, or pass arbitrary string as a table name

This makes it possible to use Arel to query against functions, e.g., generate_series in PostgreSQL, or json_each, or whatever

Author: palkan

activerecord/lib/arel/table.rb

@@ -14,7 +14,14 @@ class << self; attr_accessor :engine; end
     alias :table_name :name
 
     def initialize(name, as: nil, klass: nil, type_caster: klass&.type_caster)
-      @name = name.to_s
+      @name =
+        case name
+        when Symbol then name.to_s
+        when Nodes::Node then Arel.sql(name.to_sql)
+        else
+          name
+        end
+
       @klass = klass
       @type_caster = type_caster
 

activerecord/test/cases/arel/table_test.rb

@@ -127,6 +127,19 @@ class TableTest < Arel::Spec
         rel = Table.new :users, as: "users"
         _(rel.table_alias).must_be_nil
       end
+
+      it "should accept literal SQL"  do
+        rel = Table.new Arel.sql("generate_series(4, 2)")
+        manager = rel.project(Arel.star)
+        _(manager.to_sql).must_be_like %{ SELECT * FROM generate_series(4, 2) }
+      end
+
+      it "should accept Arel nodes"  do
+        node = Arel::Nodes::NamedFunction.new("generate_series", [4, 2])
+        rel = Table.new node
+        manager = rel.project(Arel.star)
+        _(manager.to_sql).must_be_like %{ SELECT * FROM generate_series(4, 2) }
+      end
     end
 
     describe "order" do