Add Model.qualified_primary_key for returning a qualified version of the model's primary key

Author: jeremyevans

CHANGELOG

@@ -1,5 +1,7 @@
 === master
 
+* Add Model.qualified_primary_key for returning a qualified version of the model's primary key (jeremyevans)
+
 * Support sql_literal_allow_caching? method on objects that respond to sql_literal_append/sql_literal (jeremyevans)
 
 * Support set_column_not_null as a reversible migration method (jeremyevans)

lib/sequel/model/base.rb

@@ -533,10 +533,28 @@ def primary_key_hash(value)
         end
       end
 
+      # Return a qualified identifier or array of qualified identifiers for
+      # the model's primary key.  Uses the given qualifier if provided, or
+      # the table_name otherwise. If the model does not have a primary key,
+      # raises an +Error+.
+      #
+      #   Artist.order(Artist.qualified_primary_key)
+      #   # SELECT * FROM artists ORDER BY artists.id
+      def qualified_primary_key(qualifier=table_name)
+        case key = @primary_key
+        when Symbol
+          SQL::QualifiedIdentifier.new(qualifier, key)
+        when Array
+          key.map{|k| SQL::QualifiedIdentifier.new(qualifier, k)}
+        else
+          raise(Error, "#{self} does not have a primary key")
+        end
+      end
+
       # Return a hash where the keys are qualified column references.  Uses the given
       # qualifier if provided, or the table_name otherwise. This is useful if you
       # plan to join other tables to this table and you want the column references
-      # to be qualified.
+      # to be qualified. If the model does not have a primary key, raises an +Error+.
       #
       #   Artist.where(Artist.qualified_primary_key_hash(1))
       #   # SELECT * FROM artists WHERE (artists.id = 1)

spec/model/base_spec.rb

@@ -548,6 +548,32 @@ class ::Leopard < Feline; end
   end
 end
 
+describe "Model.qualified_primary_key" do
+  before do
+    @c = Class.new(Sequel::Model(:items))
+  end
+  
+  it "should handle a single primary key" do
+    @c.qualified_primary_key.must_equal(Sequel.qualify(:items, :id))
+  end
+
+  it "should handle a composite primary key" do
+    @c.set_primary_key([:id1, :id2])
+    @c.qualified_primary_key.must_equal([Sequel.qualify(:items, :id1), Sequel.qualify(:items, :id2)])
+  end
+
+  it "should raise an error for no primary key" do
+    @c.no_primary_key
+    proc{@c.qualified_primary_key}.must_raise(Sequel::Error)
+  end
+
+  it "should allow specifying a different qualifier" do
+    @c.qualified_primary_key(:apple).must_equal(Sequel.qualify(:apple, :id))
+    @c.set_primary_key([:id1, :id2])
+    @c.qualified_primary_key(:bear).must_equal([Sequel.qualify(:bear, :id1), Sequel.qualify(:bear, :id2)])
+  end
+end
+
 describe "Model.db" do
   before do
     @db = Sequel.mock