Rails 4: Joins vs Includes: Why different results with nested association? -

Rails 4: Joins vs Includes: Why different results with nested association? -

in rails 4 app, have 2 models:

merchant has_many :offering_specials

offeringspecial belongs_to :merchant

i want retrieve merchants , special offerings open (with status_code: "op")

i tried this:

@merchants = merchant.joins(:offering_specials).where(offering_specials: { status_code: "op" })

this query:

merchant load (0.4ms) select `merchants`.* `merchants` inner bring together `offering_specials` on `offering_specials`.`merchant_id` = `merchants`.`id` `offering_specials`.`status_code` = 'op'

but retrieved offering specials, both open ("op") , pending ("pn").

however, using includes worked:

@merchants = merchant.joins(:offering_specials).where(offering_specials: { status_code: "op" })

this retrieved open offering specials. @ much slower query:

sql (19.9ms) select `merchants`.`id` t0_r0, `merchants`.`name` t0_r1, `merchants`.`slug` t0_r2, `merchants`.`url` t0_r3, `merchants`.`summary` t0_r4, `merchants`.`description` t0_r5, `merchants`.`active_for_display` t0_r6, `merchants`.`active_for_offerings_by_merchant` t0_r7, `merchants`.`active_for_offerings_by_legatocard` t0_r8, `merchants`.`credit_limit` t0_r9, `merchants`.`search_location_code` t0_r10, `merchants`.`image_file_name` t0_r11, `merchants`.`image_file_size` t0_r12, `merchants`.`image_content_type` t0_r13, `merchants`.`image_updated_at` t0_r14, `merchants`.`logo_file_name` t0_r15, `merchants`.`logo_file_size` t0_r16, `merchants`.`logo_content_type` t0_r17, `merchants`.`logo_updated_at` t0_r18, `merchants`.`created_at` t0_r19, `merchants`.`updated_at` t0_r20, `offering_specials`.`id` t1_r0, `offering_specials`.`special_number` t1_r1, `offering_specials`.`merchant_id` t1_r2, `offering_specials`.`merchant_user_id` t1_r3, `offering_specials`.`nonprofit_percentage` t1_r4, `offering_specials`.`discount_percentage` t1_r5, `offering_specials`.`start_at` t1_r6, `offering_specials`.`end_at` t1_r7, `offering_specials`.`closed_at` t1_r8, `offering_specials`.`max_dollar_amount_for_offering` t1_r9, `offering_specials`.`max_dollar_amount_per_buyer` t1_r10, `offering_specials`.`status_code` t1_r11, `offering_specials`.`created_at` t1_r12, `offering_specials`.`updated_at` t1_r13 `merchants` left outer bring together `offering_specials` on `offering_specials`.`merchant_id` = `merchants`.`id` `offering_specials`.`status_code` = 'op'

how can acquire query work joins, instead of includes?

queries of sort not homecoming associated records. you're requesting list of merchants, , that's get. when subsequently request associated offeringspecials of 1 of merchants, new query executed (which should see in logs), , of them, because did not specify otherwise. code in question not include place this, must doing somewhere, in order offeringspecials.

using includes asks eager-load association, means subject restrictions of query, why you're seeing work when way. it's slower because it's fetching records now, instead of doing separately later.

if want refactor using .joins, need add together conditional line fetch .offering_specials of merchant:

@merchants.each |m| m.offering_specials.where(:status_code => 'op') end

however, should read on why eager loading exists before doing - either getting improve performance doing 1 slower query vs. many fast ones, or if number of merchant records involve passes threshold (which may or may not happen, depending on nature of app).

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