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Elixir Ecto: 入门上手

简介

Ecto 分为4个主要组件

组件	说明
`Ecto.Repo`	数据库包装器, 通过它可以执行创建,更新,删除和查询等数据库操作, 它需要一个适配器和一个URL与数据库通信
`Ecto.Schema`	允许开发者定义映射到底层存储的数据结构
`Ecto.Changeset`	为开发者提供了一个过滤和转换外部参数的方法, 以及在发送到数据库之前追踪和验证变更的机制.
`Ecto.Query`	以Elixir语法编写查询, 从数据库检索信息. 在Ecto中查询是安全的, 避免了类似SQL注入, 等常见的问题. 并提供类型安全. 通过 `Ecto.Queryable` 协议, 查询是可组合的

配置 `Ecto`

本节包含详细的创建, 配置, 开发一个Ecto项目的完整过程. 本文基于 Ecto 2.0.0-rc 版本, 演示下面的过程.

创建项目

➜  /tmp> mix new ecto_test * creating README.md * creating .gitignore * creating mix.exs * creating config * creating config/config.exs * creating lib * creating lib/ecto_test.ex * creating test * creating test/test_helper.exs * creating test/ecto_test_test.exs  Your Mix project was created successfully. You can use "mix" to compile it, test it, and more:      cd ecto_test     mix test  Run "mix help" for more commands.

添加依赖

defp deps do   [     {:mariaex, "~> 0.7.4"},     {:ecto, "~> 2.0.0-rc.3"}   ] end

设置OTP应用

def application do   [applications: [:logger, :mariaex, :ecto]] end

获取依赖

➜  ecto_test> mix deps.get A new Hex version is available (0.11.5), please update with `mix local.hex` Running dependency resolution Dependency resolution completed   connection: 1.0.2   db_connection: 0.2.5   decimal: 1.1.2   ecto: 2.0.0-rc.3   mariaex: 0.7.4   poolboy: 1.5.1 * Getting mariaex (Hex package) Checking package (https://s3.amazonaws.com/s3.hex.pm/tarballs/mariaex-0.7.4.tar) Fetched package * Getting ecto (Hex package) Checking package (https://s3.amazonaws.com/s3.hex.pm/tarballs/ecto-2.0.0-rc.3.tar) Fetched package * Getting poolboy (Hex package) Checking package (https://s3.amazonaws.com/s3.hex.pm/tarballs/poolboy-1.5.1.tar) Using locally cached package * Getting decimal (Hex package) Checking package (https://s3.amazonaws.com/s3.hex.pm/tarballs/decimal-1.1.2.tar) Using locally cached package * Getting db_connection (Hex package) Checking package (https://s3.amazonaws.com/s3.hex.pm/tarballs/db_connection-0.2.5.tar) Using locally cached package * Getting connection (Hex package) Checking package (https://s3.amazonaws.com/s3.hex.pm/tarballs/connection-1.0.2.tar) Using locally cached package

配置数据库

在 config/config.exs 配置文件中添加如下配置:

config :ecto_test, EctoTest.Repo,   adapter: Ecto.Adapters.MySQL,   database: "ecto_test",   username: "root",   password: "root",   hostname: "192.168.212.129"  # URL 配置方式 config :ecto_test, ecto_repos: [EctoTest.Repo]   url: "mysql://root:root@192.168.212.129/ecto_test"

关于数据库配置的详细参数, 参考 https://hexdocs.pm/ecto/2.0.0-rc.1/Ecto.Adapters.MySQL.html

编写 `Repo` 模块

创建 lib/ecto_test 目录, 并在其中创建文件 repo.ex , 内容如下:

defmodule EctoTest.Repo do   use Ecto.Repo, otp_app: :ecto_test end

编译

➜  ecto_test> mix compile ==> connection Compiled lib/connection.ex Generated connection app ==> poolboy (compile) Compiled src/poolboy_sup.erl Compiled src/poolboy_worker.erl Compiled src/poolboy.erl ==> decimal Compiled lib/decimal.ex Generated decimal app ==> db_connection Compiled lib/db_connection/app.ex Compiled lib/db_connection/error.ex Compiled lib/db_connection/log_entry.ex ... ... ...

创建数据库

➜  ecto_test> mix ecto.create -r EctoTest.Repo The database for EctoTest.Repo has been created

上面的输出提示, 底层的数据库已经创建完成.

创建模型和迁移(Migration)

这一节正式开始说明如何创建模型模块, 和迁移模块

创建模型

defmodule EctoTest.Domain do   use Ecto.Schema   schema "domain" do     field :url     timestamps   end end

创建移植脚本

创建一个空的移植脚本

➜  ecto_test> mix ecto.gen.migration add_domain_table -r EctoTest.Repo * creating priv/repo/migrations * creating priv/repo/migrations/20160427032452_add_domain_table.exs

修改移植脚本 priv/repo/migrations/20160427032452_add_domain_table.exs , 为如下内容, 移植脚本默认会创建在项目根目录的 priv 子目录中. 该目录的位置可以在数据库配置中, 通过指定 :priv 键设置.

defmodule EctoTest.Repo.Migrations.AddDomainTable do   use Ecto.Migration    def change do     create table(:domain) do       add :url, :string       timestamps     end   end end

执行表的创建

➜  ecto_test> mix ecto.migrate -r EctoTest.Repo  11:29:30.396 [info]  == Running EctoTest.Repo.Migrations.AddDomainTable.change/0 forward 11:29:30.396 [info]  create table domain 11:29:30.406 [info]  == Migrated in 0.0s

在IEx中测试

iex(3)> domain = %EctoTest.Domain{url: "https://segmentfault.com/u/developerworks"} %EctoTest.Domain{__meta__: #Ecto.Schema.Metadata<:built>, id: nil, inserted_at: nil, updated_at: nil, url: "https://segmentfault.com/u/developerworks"}  iex(4)> domain |> EctoTest.Repo.insert  12:04:36.455 [debug] QUERY OK db=10.0ms queue=0.1ms INSERT INTO `domain` (`inserted_at`,`updated_at`,`url`) VALUES (?,?,?) [{{2016, 4, 27}, {4, 4, 36, 0}}, {{2016, 4, 27}, {4, 4, 36, 0}}, "https://segmentfault.com/u/developerworks"] {:ok, %EctoTest.Domain{__meta__: #Ecto.Schema.Metadata<:loaded>, id: 2, inserted_at: #Ecto.DateTime<2016-04-27 04:04:36>, updated_at: #Ecto.DateTime<2016-04-27 04:04:36>, url: "https://segmentfault.com/u/developerworks"}} iex(5)>

原文 https://segmentfault.com/a/1190000005016957

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