1

ユーザーhas_manyのコメント。コメントはcomments表の中にあります (多態的)。

User.where("comments.commentable_type = ? AND comments.commentable_id = ?", "Post", post.id).uniq

私は得る：

Post Load (0.4ms)  SELECT `posts`.* FROM `posts` LIMIT 1
TypeError: Cannot visit Arel::Nodes::Distinct
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/visitor.rb:25:in `rescue in visit'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/visitor.rb:19:in `visit'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/to_sql.rb:133:in `visit_Arel_Nodes_SelectCore'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/mysql.rb:41:in `visit_Arel_Nodes_SelectCore'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/to_sql.rb:121:in `block in visit_Arel_Nodes_SelectStatement'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/to_sql.rb:121:in `map'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/to_sql.rb:121:in `visit_Arel_Nodes_SelectStatement'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/mysql.rb:36:in `visit_Arel_Nodes_SelectStatement'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/visitor.rb:19:in `visit'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/visitor.rb:5:in `accept'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/to_sql.rb:19:in `accept'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/arel-3.0.2/lib/arel/visitors/bind_visitor.rb:11:in `accept'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/connection_adapters/abstract/database_statements.rb:7:in `to_sql'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/connection_adapters/abstract/database_statements.rb:18:in `select_all'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/connection_adapters/abstract/query_cache.rb:63:in `select_all'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/querying.rb:38:in `block in find_by_sql'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/explain.rb:40:in `logging_query_plan'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/querying.rb:37:in `find_by_sql'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/relation.rb:171:in `exec_queries'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/relation.rb:160:in `block in to_a'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/explain.rb:33:in `logging_query_plan'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/relation.rb:159:in `to_a'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/activerecord-3.2.3/lib/active_record/relation.rb:496:in `inspect'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/railties-3.2.3/lib/rails/commands/console.rb:47:in `start'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/railties-3.2.3/lib/rails/commands/console.rb:8:in `start'
        from /Users/.rvm/gems/ruby-1.9.3-p125@myapp/gems/railties-3.2.3/lib/rails/commands.rb:41:in `<top (required)>'
        from script/rails:6:in `require'

がなく.uniqても機能しますが、重複する場合を除いて、次のことを試すことができます。

User.where("comments.commentable_type = ? AND comments.commentable_id = ?", "Post", post.id).to_a.uniq

そしてそれは機能します...しかし、私はその方法が好きではありません! 他に方法はありますか？

4

3 に答える 3

1

Rails サーバー セッションを再起動します。

于 2013-04-15T20:45:29.070 に答える
1

これは、直面している同じ問題に関連する github の問題へのリンクです。

Rails 4 を使用している場合は、.distinct代わりに を使用してみてください.uniq。

于 2013-10-02T18:46:18.030 に答える
0

似たような問題がいくつかあったことを覚えています。最初にSQLのdistinctを使用します（uniqに似ていると思われます）。2番目に（これが最善の方法ではないことはわかっています）、すべてを選択してから、通常の配列をフィルタリングするのと同じように、通常の配列uniq関数を使用してフィルタリングすることができます（これは物事を進めるためです）.

于 2012-06-14T16:38:18.930 に答える