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Elixir Ecto: 模型的嵌入(Embed)

Postgres 9.4 及其以上版本可以存储类似 arrays , json , jsonb 这样的非结构化数据. Ecto 作为一个 Elixir 的数据封装器, 提供了这些非结构话的数据到 Elixir 原生数据类型的序列化和反序列化. 嵌入的记录具有所有常规模型所具有的东西, 比如结构化的字段, 生命周期回调, 变更集. 下面研究如何把结构嵌入到 Ecto 模型当中.

使用 `embeds_one` 嵌入单个结构

可以使用 embeds_one 嵌入单个结构到 Ecto 模型当中. 嵌入的字段必须是 :map 这种非结构化的的数据类型. 在 Postgres 中, Ecto 使用了 jsonb 作为底层数据库字段的数据类型.

20160430043543_create_table_account.exs

defmodule EctoTest.Repo.Migrations.CreateTableAccount do   use Ecto.Migration   def change do     create table(:accounts) do       add :name, :string       add :settings, :map  # 迁移脚本里面数据类型需要设置为 :map,                            # 这样 Postgrex 适配器才能正确的把它映射到 jsonb[] 数据类型     end   end end

执行项目目录中的 ./migrate 脚本, 内容如下

#!/bin/bash  mix ecto.migrate -r EctoTest.Repo

➜  ecto_test git:(master) ✗ ./migrate  12:38:10.930 [info]  == Running EctoTest.Repo.Migrations.CreateTableAccount.change/0 forward  12:38:10.930 [info]  create table accounts  12:38:10.943 [info]  == Migrated in 0.0s

定义模型

defmodule EctoTest.Model.Account do   use Ecto.Schema   alias EctoTest.Model.Settings   schema "accounts" do     field :name     embeds_one :settings, Settings   end end

定义嵌入到 EctoTest.Model.Account 模型中的字段:

defmodule EctoTest.Model.Settings do   use Ecto.Model   embedded_schema do     field :email_signature     field :send_emails, :boolean   end end

嵌入的记录行为上和电信的关联( associations )一样, 只是它只能够通过变更集( changeset )来更新和删除

插入数据测试

# 模拟 EctoTest.get/1 返回一个 %EctoTest.Model.Account() 结构 account = %EctoTest.Model.Account{name: "test"}  # 创建Settings结构 settings = %EctoTest.Model.Settings{email_signature: "developerworks", send_emails: true}  # 创建变更集 changeset = Ecto.Changeset.change(account)  # 嵌入 changeset = Ecto.Changeset.put_embed(changeset, :settings, settings)  # 插入数据 changeset |> EctoTest.Repo.insert!

当父记录保存时, 会自动地的调用嵌入模型( Settings 模型)中的 changeset/2 函数.

嵌入的记录可以通过 . 符号来访问, 因此不必考虑在一般的关联关系中的链接 JOIN 和预加载( preload )的问题:

account = Repo.get!(EctoTest.Model.Account, 1) account.settings #=> %Settings{...}

使用 `embeds_many` 嵌入多个结构

embeds_many 允许你嵌入一个 Ecto 结构数组到一个关系数据库字段中. 在数据库底层 Postgres 使用了 array 和 jsonb 数据类型来实现 embeds_many .

defmodule EctoTest.Repo.Migrations.CreateTablePeople do   use Ecto.Migration    def up do     create table(:people) do       add :name, :string       add :address, {:array, :map}, default: []     end   end    def down do     drop table(:people)   end end

定义 Person , Address 模型:

defmodule EctoTest.Model.Person do   use Ecto.Schema   alias EctoTest.Model.Address    schema "people" do     field :name     embeds_many :addresses, Address   end    def test_insert do     changeset = Ecto.Changeset.change(%__MODULE__{})     addresses = [       %Address{street_name: "20 Foobar Street",city: "Boston",state: "MA",zip_code: "02111"},       %Address{street_name: "1 Finite Loop", city: "Cupertino",state: "CA",zip_code: "95014"}     ]     changeset = Ecto.Changeset.put_embed(changeset, :addresses, addresses)     Repo.insert!(changeset)   end end   defmodule EctoTest.Model.Address do   use Ecto.Schema    embedded_schema do     field :street_name     field :city     field :state     field :zip_code   end end

设置多对多字段的值

iex(1)> EctoTest.Model.Person.test_insert  13:44:25.731 [debug] QUERY OK db=9.4ms INSERT INTO "people" ("addresses") VALUES ($1) RETURNING "id" [[%{city: "Boston", id: "2de7fd44-a1cf-44cd-a060-d6260325ac90", state: "MA", street_name: "20 Foobar Street", zip_code: "02111"}, %{city: "Cupertino", id: "bb65fd96-f1b1-4f0d-a92e-712884e40a7c", state: "CA", street_name: "1 Finite Loop", zip_code: "95014"}]] %EctoTest.Model.Person{__meta__: #Ecto.Schema.Metadata<:loaded>,  addresses: [%EctoTest.Model.Address{city: "Boston", id: "2de7fd44-a1cf-44cd-a060-d6260325ac90", state: "MA",    street_name: "20 Foobar Street", zip_code: "02111"},   %EctoTest.Model.Address{city: "Cupertino", id: "bb65fd96-f1b1-4f0d-a92e-712884e40a7c", state: "CA",    street_name: "1 Finite Loop", zip_code: "95014"}], id: 1, name: nil}

像 has_many 一样访问:

iex(2)> person = EctoTest.Repo.get!(EctoTest.Model.Person, 1)  13:45:04.634 [debug] QUERY OK db=1.4ms decode=9.5ms SELECT p0."id", p0."name", p0."addresses" FROM "people" AS p0 WHERE (p0."id" = $1) [1] %EctoTest.Model.Person{__meta__: #Ecto.Schema.Metadata<:loaded>,  addresses: [%EctoTest.Model.Address{city: "Boston", id: "2de7fd44-a1cf-44cd-a060-d6260325ac90", state: "MA",    street_name: "20 Foobar Street", zip_code: "02111"},   %EctoTest.Model.Address{city: "Cupertino", id: "bb65fd96-f1b1-4f0d-a92e-712884e40a7c", state: "CA",    street_name: "1 Finite Loop", zip_code: "95014"}], id: 1, name: nil}  iex(3)> person.addresses [%EctoTest.Model.Address{city: "Boston", id: "2de7fd44-a1cf-44cd-a060-d6260325ac90", state: "MA",   street_name: "20 Foobar Street", zip_code: "02111"},  %EctoTest.Model.Address{city: "Cupertino", id: "bb65fd96-f1b1-4f0d-a92e-712884e40a7c", state: "CA",   street_name: "1 Finite Loop", zip_code: "95014"}]