Correctly handle more than 2 hierarchy levels in the single table inh…

…eritance plugin

Previously, Sequel did not handle more than 2 hierarchy levels in
the single table inheritance plugin.  If you were using more than
two levels, the documentation told you that you had to set up your
own custom filter.

With this change, you can now have as many class hierarchy levels
as you want, and Sequel will handle things automatically.

There shouldn't be any backwards compatibility problems, but this
does switch subclasses to use IN instead of = in their filter. That
may have performance implications, but any decent database is going
to treat an IN with one element the same as an =, so there should
not be any performance regression in the 2 level hierarchy case.

CHANGELOG

@@ -1,5 +1,7 @@
 === HEAD
 
+* Correctly handle more than 2 hierarchy levels in the single table inheritance plugin (jeremyevans)
+
 * Allow using a custom column value<->class mapping to the single_table_inheritance plugin (jeremyevans, tmm1)
 
 * Handle SQL::Identifiers in the schema_dumper extension (jeremyevans) (#304)

lib/sequel/plugins/single_table_inheritance.rb

@@ -20,11 +20,6 @@ module Plugins
     # direct class references in the plugin class.  You should specify subclasses
     # in the plugin call using class name strings or symbols, see usage below.
     #   
-    # The filters and row_proc that sti_key sets up in subclasses may not work correctly if
-    # those subclasses have further subclasses.  For those middle subclasses,
-    # you may need to call set_dataset manually with the correct filter and
-    # row_proc.
-    # 
     # Usage:
     #
     #   # Use the default of storing the class name in the sti_key
@@ -56,6 +51,7 @@ module SingleTableInheritance
       # Setup the necessary STI variables, see the module RDoc for SingleTableInheritance
       def self.configure(model, key, opts={})
         model.instance_eval do
+          @sti_key_array = nil
           @sti_key = key 
           @sti_dataset = dataset
           @sti_model_map = opts[:model_map] || lambda{|v| v if v && v != ''}
@@ -87,6 +83,10 @@ module ClassMethods
         # The column name holding the STI key for this model
         attr_reader :sti_key
 
+        # Array holding keys for all subclasses of this class, used for the
+        # dataset filter in subclasses. Nil in the main class.
+        attr_reader :sti_key_array
+
         # A hash/proc with class keys and column value values, mapping
         # the the class to a particular value given to the sti_key column.
         # Used to set the column value when creating objects, and for the
@@ -105,9 +105,13 @@ def inherited(subclass)
           sd = sti_dataset
           skm = sti_key_map
           smm = sti_model_map
-          subclass.set_dataset(sd.filter(SQL::QualifiedIdentifier.new(table_name, sk)=>skm[subclass]), :inherited=>true)
+          key = skm[subclass] 
+          sti_subclass_added(key)
+          ska = [key]
+          subclass.set_dataset(sd.filter(SQL::QualifiedIdentifier.new(table_name, sk)=>ska), :inherited=>true)
           subclass.instance_eval do
             @sti_key = sk
+            @sti_key_array = ska
             @sti_dataset = sd
             @sti_key_map = skm
             @sti_model_map = smm
@@ -121,6 +125,15 @@ def sti_load(r)
           sti_class(sti_model_map[r[sti_key]]).load(r)
         end
 
+        # Make sure that all subclasses of the parent class correctly include 
+        # keys for all of their descendant classes.
+        def sti_subclass_added(key)
+          if sti_key_array
+            sti_key_array << key
+            superclass.sti_subclass_added(key)
+          end
+        end
+
         private
 
         # Return a class object.  If a class is given, return it directly.

spec/extensions/single_table_inheritance_spec.rb

@@ -41,8 +41,8 @@ def @ds.fetch_rows(sql)
     end 
     StiTest.all.collect{|x| x.class}.should == [StiTest, StiTestSub1, StiTestSub2]
     StiTest.dataset.sql.should == "SELECT * FROM sti_tests"
-    StiTestSub1.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.blah = 'StiTestSub1')"
-    StiTestSub2.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.blah = 'StiTestSub2')"
+    StiTestSub1.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.blah IN ('StiTestSub1'))"
+    StiTestSub2.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.blah IN ('StiTestSub2'))"
   end 
 
   it "should return rows with the correct class based on the polymorphic_key value" do
@@ -90,8 +90,21 @@ def @ds.fetch_rows(sql)
 
   it "should add a filter to model datasets inside subclasses hook to only retreive objects with the matching key" do
     StiTest.dataset.sql.should == "SELECT * FROM sti_tests"
-    StiTestSub1.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind = 'StiTestSub1')"
-    StiTestSub2.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind = 'StiTestSub2')"
+    StiTestSub1.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub1'))"
+    StiTestSub2.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub2'))"
+  end
+
+  it "should add a correct filter for multiple levels of subclasses" do
+    class ::StiTestSub1A < StiTestSub1; end
+    StiTestSub1.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub1', 'StiTestSub1A'))"
+    StiTestSub1A.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub1A'))"
+    class ::StiTestSub2A < StiTestSub2; end
+    StiTestSub2.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub2', 'StiTestSub2A'))"
+    StiTestSub2A.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub2A'))"
+    class ::StiTestSub1B < StiTestSub1A; end
+    StiTestSub1.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub1', 'StiTestSub1A', 'StiTestSub1B'))"
+    StiTestSub1A.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub1A', 'StiTestSub1B'))"
+    StiTestSub1B.dataset.sql.should == "SELECT * FROM sti_tests WHERE (sti_tests.kind IN ('StiTestSub1B'))"
   end
 
   context "with custom options" do