EntityFrameworkCore使用Migrations自动更新数据库

来源:转载

EntityFrameworkCore使用Migrations自动更新数据库

系统环境:Win10IDE:VS2017 RC4.netcore版本:1.1

一、新建ASP.NET Core WebApi项目

二、引用Microsoft.EntityFrameworkCore.Sqlite

使用VS Nuget工具,添加对Microsoft.EntityFrameworkCore.Sqlite库的引用,如使用其他数据库,添加相对应的引用即可。

三、使项目支持dotnet ef工具以使用Migrations

手动修改项目csproj文件

ItemGroup.DotNetCliToolReference节点添加Microsoft.EntityFrameworkCore.Tools.DotNet工具的引用,注意版本1.0.0-msbuild3-final,VS2017 RC4 用的是MSBuild格式。并在ItemGroup.PackageReference节点添加对Microsoft.EntityFrameworkCore.Design的引用,因为使用dotnet ef migrations add命令需要该引用。

 <ItemGroup> ······ <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="1.1.0" /> ······ </ItemGroup> <ItemGroup> ······ <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="1.0.0-msbuild3-final" /> </ItemGroup>

手动添加的原因是我在Nuget添加Microsoft.EntityFrameworkCore.Tools.DotNet时,报了一个错,可能是VS2017 RC版本的BUG:

Package 'Microsoft.EntityFrameworkCore.Tools.DotNet 1.1.0-preview4-final' has a package type 'DotnetCliTool' that is not supported by project 'EntityFrameworkCoreMigrationsDemo'.

CMD命令行cd到项目目录下(非Solution目录),执行dotnet builddotnet ef

C:/WorkSpacesC/DotNetCore/EntityFrameworkCoreMigrationsDemo/EntityFrameworkCoreMigrationsDemo>dotnet buildMicrosoft (R) Build Engine version 15.1.545.13942Copyright (C) Microsoft Corporation. All rights reserved.Startup.cs(45,13): warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call. [C:/WorkSpacesC/DotNetCore/EntityFrameworkCoreMigrationsDemo/EntityFrameworkCoreMigrationsDemo/EntityFrameworkCoreMigrationsDemo.csproj] EntityFrameworkCoreMigrationsDemo -> C:/WorkSpacesC/DotNetCore/EntityFrameworkCoreMigrationsDemo/EntityFrameworkCoreMigrationsDemo/bin/Debug/netcoreapp1.0/EntityFrameworkCoreMigrationsDemo.dllBuild succeeded.Startup.cs(45,13): warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call. [C:/WorkSpacesC/DotNetCore/EntityFrameworkCoreMigrationsDemo/EntityFrameworkCoreMigrationsDemo/EntityFrameworkCoreMigrationsDemo.csproj] 1 Warning(s) 0 Error(s)Time Elapsed 00:00:04.76C:/WorkSpacesC/DotNetCore/EntityFrameworkCoreMigrationsDemo/EntityFrameworkCoreMigrationsDemo>dotnet ef _//__ ---==/ // ___ ___ |. /|/ | __|| __| | ) /// | _| | _| /_/ | //|// |___||_| / //////Entity Framework Core .NET Command Line Tools 1.0.0-msbuild3-finalUsage: dotnet ef [options] [command]Options: --version Show version information -h|--help Show help information -v|--verbose Show verbose output. --no-color Don't colorize output. --prefix-output Prefix output with level.Commands: database Commands to manage the database. dbcontext Commands to manage DbContext types. migrations Commands to manage migrations.Use "dotnet ef [command] --help" for more information about a command.

可以看到EF独角兽,说明工具引用成功。

四、创建实例DbContext

新建DbContext以及相关Models

using Microsoft.EntityFrameworkCore;using System.Collections.Generic;namespace EntityFrameworkCoreMigrationsDemo.Data{ public class BloggingContext : DbContext { public DbSet<Blog> Blogs { get; set; } public DbSet<Post> Posts { get; set; } protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { optionsBuilder.UseSqlite("Filename=./Blogging.db"); } } public class Blog { public int BlogId { get; set; } public string Url { get; set; } public List<Post> Posts { get; set; } } public class Post { public int PostId { get; set; } public string Title { get; set; } public string Content { get; set; } public int BlogId { get; set; } public Blog Blog { get; set; } }}

在Startup将DbContext注册为服务

namespace EntityFrameworkCoreMigrationsDemo{ public class Startup { ······ public void ConfigureServices(IServiceCollection services) { ······ services.AddDbContext<BloggingContext>(); } ······ }}

五、使用Migrations

新建数据库初始化类InitializeAsync.cs

using Microsoft.EntityFrameworkCore;using System.Threading.Tasks;namespace EntityFrameworkCoreMigrationsDemo.Data{ public class DbInitializer { public async Task InitializeAsync(BloggingContext context) { //var migrations = await context.Database.GetPendingMigrationsAsync();//获取未应用的Migrations,不必要,MigrateAsync方法会自动处理 await context.Database.MigrateAsync();//根据Migrations修改/创建数据库 } }}

在Startup.cs的Configure方法中,添加参数BloggingContext context,netcore会使用DI将DbContext注入到Configure方法,并添加对DbInitializer的调用。

 public class Startup { ······ public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, BloggingContext context) { ······ new DbInitializer().InitializeAsync(context); } }

使用dotnet ef命令创建Migrations:dotnet ef migrations add [NAME]

C:/WorkSpacesC/DotNetCore/EntityFrameworkCoreMigrationsDemo/EntityFrameworkCoreMigrationsDemo>dotnet ef migrations add InitialBuild succeeded. 0 Warning(s) 0 Error(s)Time Elapsed 00:00:02.32Done. To undo this action, use 'ef migrations remove'

执行成功后,可以看到项目目录下多了个文件夹Migrations,里面就是自动生成的Migrations文件。

创建更新Migrations的命令跟创建初始的一样,只是最后一个参数自己定义即可。

最后执行代码,成功创建了新的数据库,并且里面有一个表__EFMigrationsHistory,是自动生成的用来记录Migrations记录。

修改Blog类,添加一个字段public string NewField { get; set; },在命令行执行命令dotnet ef migrations add NewField,然后运行程序,可以看到数据库已经更新,__EFMigrationsHistory表也多了一条对应的记录。

其他说明

因为我习惯使用VS,但是构建这个项目的过程中,需要使用到命令行,还需要手动修改csproj文件,所以这篇文章的操作过程有可能点乱,我自己在写Demo的时候,也是多次重启VS使VS能够加载最新的项目。

Demo源码,测试通过:Github

参考:.NET Core - New Database Create your modelWalkthrough: Entity Framework Core 1.1 with Migrations

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