Question

我在控制台中注意到to_a中ActiveRecord_Relation方法的异常用户。我将在下面复制它：

从表格中选择变量a：

a = Crypto::ExchangeQuotation.all
[DEBUG]   Crypto::ExchangeQuotation Load (121.1ms)  SELECT  "crypto_exchange_quotations".* FROM "crypto_exchange_quotations" LIMIT $1  [["LIMIT", 11]]

致电a：

2.4.1 :003 > a
[DEBUG]   Crypto::ExchangeQuotation Load (0.8ms)  SELECT  "crypto_exchange_quotations".* FROM "crypto_exchange_quotations" LIMIT $1  [["LIMIT", 11]]

a到数组：

2.4.1 :004 > a.to_a
[DEBUG]   Crypto::ExchangeQuotation Load (0.9ms)  SELECT "crypto_exchange_quotations".* FROM "crypto_exchange_quotations"

再次致电a：

2.4.1 :005 > a
 => #<ActiveRecord::Relation [#<Crypto::ExchangeQuotation id: 1, exchange_code: "ARN", base_currency_code: "BRL", currency_code: "BTC", origin: "bitvalor", created_at: "2018-03-15 23:24:06", updated_at: "2018-03-15 23:24:06", buy: 17810.0, sell: 17810.0>,

在变量中调用to_a，之后再次调用它真的避免再次重新运行查询吗？如果是，为什么？因为a中返回的内容仍然是ActiveRecord_Relation。

Answer 1

调用to_a不会改变基础对象，但它会复制它并将其作为数组返回。在这里查看to_a的广告代码：

def to_a
  records.dup
end

要真正将其更改为数组，您必须覆盖变量a

a = a.to_a

`to_a`避免重新运行查询？

1 个答案: