Let t.foreign_key use the same `to_table` twice

Previously if you used `t.foreign_key` twice within the same
`create_table` block using the same `to_table`, all statements except
the final one would fail silently. For example, the following code:

    def change
      create_table :flights do |t|
        t.integer :from_id, index: true, null: false
        t.integer :to_id,   index: true, null: false

        t.foreign_key :airports, column: :from_id
        t.foreign_key :airports, column: :to_id
      end
    end

Would only create one foreign key, on the column `from_id`.

This commit allows multiple foreign keys to the same table to be created
within one `create_table` block.

1 files changed, 20 insertions, 0 deletions

diff --git a/activerecord/test/cases/migration/references_foreign_key_test.rb b/activerecord/test/cases/migration/references_foreign_key_test.rb
index b01415afb2..c701eb312f 100644
--- a/activerecord/test/cases/migration/references_foreign_key_test.rb
+++ b/activerecord/test/cases/migration/references_foreign_key_test.rb
@@ -144,6 +144,26 @@ module ActiveRecord
           @connection.drop_table "testing", if_exists: true
         end
       end
+
+      test "multiple foreign keys can be added to the same table" do
+        @connection.create_table :testings do |t|
+          t.integer :col_1
+          t.integer :col_2
+
+          t.foreign_key :testing_parents, column: :col_1
+          t.foreign_key :testing_parents, column: :col_2
+        end
+
+        fks = @connection.foreign_keys("testings")
+
+        assert_equal fks.length, 2
+        assert_equal "testings",        fks[0].from_table
+        assert_equal "testing_parents", fks[0].to_table
+        assert_equal "col_1",           fks[0].column
+        assert_equal "testings",        fks[1].from_table
+        assert_equal "testing_parents", fks[1].to_table
+        assert_equal "col_2",           fks[1].column
+      end
     end
   end
 end