建立物件 (或多個物件)，並回傳建立的物件或建立的物件清單。

attributes 參數可以是 雜湊 或包含雜湊的 陣列。這些雜湊描述物件的屬性，準備好要建立。

範例

# Build a single new object
User.build(first_name: 'Jamie')

# Build an Array of new objects
User.build([{ first_name: 'Jamie' }, { first_name: 'Jeremy' }])

# Build a single object and pass it into a block to set other attributes.
User.build(first_name: 'Jamie') do |u|
  u.is_admin = false
end

# Building an Array of new objects using a block, where the block is executed for each object:
User.build([{ first_name: 'Jamie' }, { first_name: 'Jeremy' }]) do |u|
  u.is_admin = false
end

建立物件 (或多個物件)，在驗證通過的情況下儲存到資料庫中。無關於物件是否成功儲存到資料庫中，都會回傳生成的物件。

attributes 參數可以是 雜湊 或包含雜湊的 陣列。這些雜湊描述要建立的物件屬性。

範例

# Create a single new object
User.create(first_name: 'Jamie')

# Create an Array of new objects
User.create([{ first_name: 'Jamie' }, { first_name: 'Jeremy' }])

# Create a single object and pass it into a block to set other attributes.
User.create(first_name: 'Jamie') do |u|
  u.is_admin = false
end

# Creating an Array of new objects using a block, where the block is executed for each object:
User.create([{ first_name: 'Jamie' }, { first_name: 'Jeremy' }]) do |u|
  u.is_admin = false
end

建立物件 (或多個物件)，在驗證通過的情況下儲存到資料庫中。如果驗證失敗，會引發 RecordInvalid 錯誤，與 Base#create 不同。

attributes 參數可以是 雜湊 或包含雜湊的 陣列。這些屬性描述要建立在單一物件或多個物件 (如果提供雜湊陣列) 上的屬性。

根據屬性雜湊，instantiate 會回傳合適類別的新執行個體。僅接受字串作為金鑰。

例如，Post.all 可能透過在 type 屬性中儲存記錄的子類別，來回傳留言、訊息和電子郵件。透過呼叫 instantiate (而不是 new)，尋找方法能確保為每筆記錄取得合適類別的新執行個體。

請參閱 ActiveRecord::Inheritance#discriminate_class_for_record 來了解如何實作此「單一表格」繼承對應。

接受要在 SELECT / UPDATE / DELETE 查詢的 WHERE 子句和 `#first` 及 `#last` 檢索器方法的 ORDER BY 子句中使用的屬性名稱清單。

class Developer < ActiveRecord::Base
  query_constraints :company_id, :id
end

developer = Developer.first
# SELECT "developers".* FROM "developers" ORDER BY "developers"."company_id" ASC, "developers"."id" ASC LIMIT 1
developer.inspect # => #<Developer id: 1, company_id: 1, ...>

developer.update!(name: "Nikita")
# UPDATE "developers" SET "name" = 'Nikita' WHERE "developers"."company_id" = 1 AND "developers"."id" = 1

# It is possible to update an attribute used in the query_constraints clause:
developer.update!(company_id: 2)
# UPDATE "developers" SET "company_id" = 2 WHERE "developers"."company_id" = 1 AND "developers"."id" = 1

developer.name = "Bob"
developer.save!
# UPDATE "developers" SET "name" = 'Bob' WHERE "developers"."company_id" = 1 AND "developers"."id" = 1

developer.destroy!
# DELETE FROM "developers" WHERE "developers"."company_id" = 1 AND "developers"."id" = 1

developer.delete
# DELETE FROM "developers" WHERE "developers"."company_id" = 1 AND "developers"."id" = 1

developer.reload
# SELECT "developers".* FROM "developers" WHERE "developers"."company_id" = 1 AND "developers"."id" = 1 LIMIT 1

更新物件（或多個物件）並將其儲存至資料庫中（如果驗證通過）。會傳回產生的物件，無論是否已將該物件成功儲存至資料庫中。

參數

• id - 應該是待更新的 id 或 id 陣列。選用參數，預設為關係中的所有記錄。

• attributes - 應該是屬性雜湊或雜湊陣列。

範例

# Updates one record
Person.update(15, user_name: "Samuel", group: "expert")

# Updates multiple records
people = { 1 => { "first_name" => "David" }, 2 => { "first_name" => "Jeremy" } }
Person.update(people.keys, people.values)

# Updates multiple records from the result of a relation
people = Person.where(group: "expert")
people.update(group: "masters")

注意：更新大量的記錄會為每個記錄執行一項 UPDATE 查詢，這可能會造成效能問題。如果不需要為每個記錄更新執行回呼，則最好使用 update_all 針對一項查詢更新所有記錄。

更新物件（或多個物件），就像使用 update 一樣，但會呼叫 update!，而不是 update，所以如果記錄無效且儲存會失敗，就會引發例外狀況。