Performance: save some queries when pluck is not needed #3160
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rhymes
commented
Jun 14, 2019
| @@ -9,7 +9,7 @@ def index | |||
| includes(:reporter, :notes). | |||
| order("feedback_messages.created_at DESC"). | |||
| page(params[:page] || 1).per(5) | |||
| @email_messages = EmailMessage.find_for_reports(@feedback_messages.pluck(:id)) | |||
| @email_messages = EmailMessage.find_for_reports(@feedback_messages) | |||
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EmailMessage.find_for_reports uses feedback messages IDs for a query.
If we don't use pluck but pass the object themselves Rails is going to issue only one query using a subselect. something like:
SELECT * FROM email_messages WHERE feedback_message_id IN (SELECT id FROM feedback_messages) instead of two separate queries
| @@ -11,7 +11,7 @@ def index | |||
| order("hotness_score DESC").limit(100) | |||
| @articles = @articles.cached_tagged_with(params[:tag]) if params[:tag].present? | |||
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| @rating_votes = RatingVote.where(article: @articles.pluck(:id), user: current_user) | |||
| @rating_votes = RatingVote.where(article: @articles, user: current_user) | |||
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Same here, Rails will transform this in a single select statement, @articles are already going to be used by the view to render the page, there's no need to extract ids pre-emptively
maestromac
approved these changes
Jun 14, 2019
pr-triage
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PR: reviewed-approved
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PR: merged
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Description
Rails
pluckforces an additional SQL query, such query is not always needed when the objects are already in memory or the requested ID is the primary key ID.Added to documentation?