UnScope 用的人應該不多，我能不用也不用，但是，總有用到時，要配合它，一開時寫SQL時，最好就是能知道他的限制。

UnScope 只能用在Hash mode，不能用在 SQL 的 Where 字串內，有點可惜...   

在 SQL 的 Hash，正常

irb> @blogs = Blog.where(block: 0).to_sql

=> "SELECT \"blogs\".* FROM \"blogs\" WHERE \"blogs\".\"block\" = 0  ORDER BY \"blogs\".\"created_at\" DESC"

irb> @blogs = Blog.where(block: 0).unscope(where: :block).to_sql

=> "SELECT \"blogs\".* FROM \"blogs\"  ORDER BY \"blogs\".\"created_at\" DESC"

在 SQL 的字串，不能動作

irb> @blogs = Blog.where("block=0").to_sql

=> "SELECT \"blogs\".* FROM \"blogs\" WHERE (block=0)  ORDER BY \"blogs\".\"created_at\" DESC"

irb> @blogs = Blog.where("block=0").unscope(where: :block).to_sql

=> "SELECT \"blogs\".* FROM \"blogs\" WHERE (block=0)  ORDER BY \"blogs\".\"created_at\" DESC"

在 SQL 的字串，全部 unscope 可行！

irb> @blogs = Blog.where("block=0").unscope(:where).to_sql

=> "SELECT \"blogs\".* FROM \"blogs\"  ORDER BY \"blogs\".\"created_at\" DESC"

rewhere 也一樣：

irb> @blogs = Blog.where("block=0").rewhere(spam_block: 1)

SELECT "blogs".* FROM "blogs" WHERE (block=0) AND "blogs"."block" = $1  ORDER BY blogs"."created_at" DESC  [["block", 1]]

 
解決的方法式混合兩種

irb> @blogs = Blog.where(block: 1).where("role_id <> 0").count

SELECT COUNT(*) FROM "blogs" WHERE "blogs"."block" = $1 AND (role_id <> 0)  [["block", 1]]

=> 3

irb> @blogs = Blog.where(block: 1).where("role_id <> 0").unscope(where: :block).count

SELECT COUNT(*) FROM "blogs" WHERE (role_id <> 0)

=> 634

irb> @pc_blogs = PcBlog.where(spam_block: 1).where("pc_role_id <> 0").unscope(where: :spam_block).where("spam_block_editor_id is not null").count

SELECT COUNT(*) FROM "pc_blogs" WHERE (pc_role_id <> 0) AND (spam_block_editor_id is not null)

=> 25

irb> @pc_blogs = PcBlog.where(spam_block: 1).where("pc_role_id <> 0").unscope(where: :spam_block).where("spam_block <>0").count

SELECT COUNT(*) FROM "pc_blogs" WHERE (pc_role_id <> 0) AND (spam_block <>0)

=> 19