Prevent N+1 query performance issues by batching database operations instead of making individual queries within loops. This is critical for application performance as each individual query adds significant overhead.
Prevent N+1 query performance issues by batching database operations instead of making individual queries within loops. This is critical for application performance as each individual query adds significant overhead.
Problem Pattern:
# BAD: N+1 queries - one query per iteration
field_ids.map do |fid|
if UserField.find_by(id: fid).field_type == "confirm" # Query per field!
# process field
end
end
# BAD: N+1 queries in user/group lookups
names.each do |name|
if user_id = User.find_by_username(name)&.id # Query per name!
user_ids << user_id
elsif group_id = Group.find_by(name: name)&.id # Query per name!
group_ids << group_id
end
end
Solution Pattern:
# GOOD: Single batch query
confirm_field_ids = UserField.where(field_type: "confirm", id: field_ids).pluck(:id)
field_ids.map do |fid|
if confirm_field_ids.include?(fid)
# process field
end
end
# GOOD: Batch queries for users and groups
found_users = User.where(username_lower: names.map(&:downcase)).pluck(:username, :id).to_h
user_ids.concat(found_users.values)
remaining_names = names - found_users.keys
group_ids.concat(Group.where(name: remaining_names).pluck(:id)) if remaining_names.present?
Always preload or batch-fetch related data before processing collections. Use where().pluck(), includes(), or joins() to minimize database round trips.
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