Active Record Where Not boolean: true

Question

I'm struggling to wrap my mind around an ActiveRecord query.

I'm trying to search my database for GolfRetailer objects with ID's 1..100, that have something (not nil) in their :website field, and that don't have true in their duplicate_domain field.

Here's the query I expected to work:

GolfRetailer.where.not(website: nil, duplicate_domain: true).where(id: 1..100)

I also tried this variant of essentially the same query: GolfRetailer.where.not(website: nil).where(id: 1..100, duplicate_domain: !true)

But both return an empty array, despite there definitely being records that meet those requirements.

When I run GolfRetailer.where.not(website: nil).where(id: 1..100) I get an array, and when I run GolfRetailer.where.not(website: nil, duplicate_domain: nil).where(id: 1..100) I also get an array, but with all records that do have the true duplicate_domain flag, which isn't what I'm looking for.

I'd rather not search for records that have duplicate_domain: nil as that's not always correct (I may not have processed their domain yet).

For clarity, here is the Schema for the Model.

create_table "golf_retailers", force: :cascade do |t|
    t.string "name"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.string "place_id"
    t.string "website"
    t.string "formatted_address"
    t.string "google_places_name"
    t.string "email"
    t.boolean "duplicate_domain"
    t.index ["duplicate_domain"], name: "index_golf_retailers_on_duplicate_domain"
  end

What am I missing to make this query work?

Answer 1

发生这种情况是因为在SQL中执行a时!= TRUE，NULL结果中将不包含任何值。这是因为该NULL值表示一个未知值，所以DB不知道如何对未知值执行任何比较操作，因此将它们排除在外。

解决此问题的一种方法是使用IS DISTINCT FROM：

GolfRetailer
  .where(id: 1..100)
  .where.not(website: nil)
  .where("duplicate_domain IS DISTINCT FROM ?", true)

正如其他人提到的那样，您还应该问自己，如果a确实GolfRetailer有一个，是否真的不为您所知duplicate_domain。

如果，所有GolfRetailer符合S duplicate_domain的NULL实际上意味着他们没有一个（false）比你应该考虑防止NULL值该列完全。

您可以通过在change_column数据库迁移的列上添加NOT NULL约束来实现。

为了添加NOT NULL约束，您首先需要确保该列中的所有数据都具有非null值。

def change
  GolfRetailer.in_batches.update_all(duplicate_domain: false)

  change_column_null :golf_retailers, :duplicate_domain
end

如果您的应用程序处于负载状态，则还应注意此类迁移可能具有的潜在性能-特别是如果您添加具有默认值的NOT NULL约束。

考虑使用诸如Strong Migrations gem之类的工具来帮助查找可能导致生产前停机的数据库迁移。