Always skip association placeholder loader if :dataset option given

The placeholder loader does not consider the :dataset option, so it
should never be used even if the association is marked as not
instance specific.  In general, a :dataset option that isn't
instance specific is unlikely, as otherwise you would get the same
associated values for every instance of the model.

lib/sequel/model/associations.rb

@@ -801,7 +801,7 @@ def union_eager_loader
 
         # Whether the placeholder loader can be used to load the association.
         def use_placeholder_loader?
-          !self[:instance_specific] && !self[:eager_graph]
+          self[:use_placeholder_loader]
         end
       end
 
@@ -1810,6 +1810,7 @@ def associate(type, name, opts = OPTS, &block)
             raise(Error, "cannot clone an association to an association of different type (association #{name} with type #{type} cloning #{opts[:clone]} with type #{cloned_assoc[:type]})")
           end
 
+          opts[:use_placeholder_loader] = !opts[:instance_specific] && !opts[:eager_graph] && !orig_opts[:dataset]
           opts[:eager_block] = opts[:block] unless opts.include?(:eager_block)
           opts[:graph_join_type] ||= :left_outer
           opts[:order_eager_graph] = true unless opts.include?(:order_eager_graph)

spec/model/associations_spec.rb

@@ -1099,6 +1099,32 @@ class Parent < Sequel::Model; end
     DB.sqls.must_equal ["SELECT * FROM nodes WHERE ((nodes.id = 100) AND (x = 100)) LIMIT 1"]
   end
 
+  it "should handle associations with :dataset option that are marked as instance specific" do
+    @c2.one_to_one :child_20, :class => @c2, :key=>:id, :instance_specific=>true, :dataset=>proc{|r| r.associated_dataset.where(:x=>100)}
+    @c2.load(:id => 100).child_20
+    DB.sqls.must_equal ["SELECT * FROM nodes WHERE (x = 100) LIMIT 1"]
+  end
+
+  it "should handle associations with :dataset option that are marked as not-instance specific" do
+    @c2.one_to_one :child_20, :class => @c2, :key=>:id, :instance_specific=>false, :dataset=>proc{|r| r.associated_dataset.where(:x=>100)}
+    @c2.load(:id => 100).child_20
+    DB.sqls.must_equal ["SELECT * FROM nodes WHERE (x = 100) LIMIT 1"]
+  end
+
+  it "should handle associations with :dataset option that are marked as instance specific when finalizing associations" do
+    @c2.one_to_one :child_20, :class => @c2, :key=>:id, :instance_specific=>true, :dataset=>proc{|r| r.associated_dataset.where(:x=>100)}
+    @c2.finalize_associations
+    @c2.load(:id => 100).child_20
+    DB.sqls.must_equal ["SELECT * FROM nodes WHERE (x = 100) LIMIT 1"]
+  end
+
+  it "should handle associations with :dataset option that are marked as not-instance specific when finalizing associations" do
+    @c2.one_to_one :child_20, :class => @c2, :key=>:id, :instance_specific=>false, :dataset=>proc{|r| r.associated_dataset.where(:x=>100)}
+    @c2.finalize_associations
+    @c2.load(:id => 100).child_20
+    DB.sqls.must_equal ["SELECT * FROM nodes WHERE (x = 100) LIMIT 1"]
+  end
+
   it "should handle associations with blocks that are marked as not-instance specific and use Sequel.delay" do
     x = 100
     @c2.one_to_one :child_20, :class => @c2, :key=>:id, :instance_specific=>false do |ds| ds.where(:x=>Sequel.delay{x}) end