ASP.NET Core 設置和初始化數據庫

上一章節中我們已經設置和配置好了 EF 框架服務，本章節我們就來學習如何使用 EF 框架設置和初始化數據庫

初始化數據庫

初始化數據庫的方法之一是使用 EF 框架來創建數據庫，僅僅需要兩步就能完成

第一步，給我們的 HelloWorld 項目添加遷移 ( migration ) 代碼

遷移代碼是 C# 代碼，用來在數據庫系統中創建數據庫

當然了，EF 框架可以自動幫我們生成遷移代碼

EF 框架通過對比數據庫和我們的模型，並計算出所需的數據庫表的更改

當我們添加其它的模型或對現有模型進行更改 ( 如 Employee 類 )時，我們可以使用 EF 框架創建新的遷移來保持我們的數據庫表同步
第二步，執行遷移代碼，更新數據庫，也就是說，我們需要明確地應用這些遷移來更新數據庫

這兩步任務都可以通過在 控制台窗口 ( 終端或 Power Shell 或 命令提示符 ) 中使用一些簡單的命令來實現

好吧，開始吧

首先打開 控制台窗口 ( 終端或 Power Shell 或 命令提示符 )，定位到我們的 HelloWorld 項目下
```
$ cd ~/Developer/aspnetcore/HelloWorld/HelloWorld
```
我用的是 macOS，且我的 HelloWorld 保存在 ~/Developer/aspnetcore/HelloWorld/HelloWorld

然后使用 ls 命名就可以列出當前目錄下的所有文件和子目錄
```
$ ls
AppSettings.json  Controllers  HelloWorld.csproj  Models  Program.cs  Properties  Startup.cs  Views  bin  obj  wwwroot
```
如果你使用的是 Windows，且使用的不是 Power Shell，那么你應該使用 dir 命令而不是 ls 命令

如果能看到 HelloWorld.csproj 則說明處於正確的目錄，否則你應該繼續 cd 到該目錄下

然后可以運行下列命令創建遷移代碼

dotnet ef migrations add InitialCreate -v

參數	說明
dotnet	是 .NET 框架所有命令的開始標識
ef	是指使用 Entity Framework 提供的命令
migrations	是指使用遷移命令
add	是指添加遷移
InitialCreate	是本次遷移的說明，你可以改成任意文本，但我們推薦最好是能清楚的描述本次遷移的意圖
-v	參數用於輸出創建遷移代碼時的運行日志，方便出錯時我們可以查看錯在哪里

運行失敗... 你知道有多坑嗎，我寫這個教程的時候才 2.1.0，寫到一半變成了 2.1.1 了

運行結果如下

$ dotnet ef migrations add InitialCreate -v
Using project '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj'.
Using startup project '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj'. Writing '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/obj/HelloWorld.csproj.EntityFrameworkCore.targets'... dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=/var/folders/yk/2446sljj6hn82nvzkdgxltmw0000gn/T/tmp9Zm0P4.tmp /verbosity:quiet /nologo /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj Writing '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/obj/HelloWorld.csproj.EntityFrameworkCore.targets'... dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=/var/folders/yk/2446sljj6hn82nvzkdgxltmw0000gn/T/tmpQa9wxL.tmp /verbosity:quiet /nologo /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj dotnet build /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj /verbosity:quiet /nologo Build succeeded. 0 Warning(s) 0 Error(s) Time Elapsed 00:00:05.31 dotnet exec --depsfile /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1/HelloWorld.deps.json --additionalprobingpath /Users/yufei/.nuget/packages --additionalprobingpath /usr/local/share/dotnet/sdk/NuGetFallbackFolder --runtimeconfig /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1/HelloWorld.runtimeconfig.json /usr/local/share/dotnet/sdk/2.1.301/DotnetTools/dotnet-ef/2.1.1/tools/netcoreapp2.1/any/tools/netcoreapp2.0/any/ef.dll migrations add InitialCreate --assembly /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1/HelloWorld.dll --startup-assembly /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1/HelloWorld.dll --project-dir /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/ --language C# --working-dir /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld --verbose --root-namespace HelloWorld Using assembly 'HelloWorld'. Using startup assembly 'HelloWorld'. Using application base '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1'. Using working directory '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld'. Using root namespace 'HelloWorld'. Using project directory '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/'. Finding DbContext classes... Finding IDesignTimeDbContextFactory implementations... Finding application service provider... Finding IWebHost accessor... Using environment 'Development'. Using application service provider from IWebHost accessor on 'Program'. Found DbContext 'HelloWorldDBContext'. Finding DbContext classes in the project... Using context 'HelloWorldDBContext'. info: Microsoft.EntityFrameworkCore.Infrastructure[10403] Entity Framework Core 2.1.1-rtm-30846 initialized 'HelloWorldDBContext' using provider 'Microsoft.EntityFrameworkCore.Sqlite' with options: None Finding design-time services for provider 'Microsoft.EntityFrameworkCore.Sqlite'... Using design-time services from provider 'Microsoft.EntityFrameworkCore.Sqlite'. Finding design-time services referenced by assembly 'HelloWorld'. No referenced design-time services were found. Finding IDesignTimeServices implementations in assembly 'HelloWorld'... No design-time services were found. Writing migration to '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/Migrations/20180623011047_InitialCreate.cs'. Writing model snapshot to '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/Migrations/HelloWorldDBContextModelSnapshot.cs'. Done. To undo this action, use 'ef migrations remove'

大概意思就是經過漫長的歲月，成功創建了遷移代碼

這一步非常容易出錯，如果你有任何錯誤，歡迎你在討論區留下你包括的意見

ASP.NET Core 討論區

創建遷移成功后，我們就可以使用下面的命令查看當前有多少遷移代碼和它們的狀態

$ dotnet ef migrations list

運行結果如下

$ dotnet ef migrations list                
info: Microsoft.EntityFrameworkCore.Infrastructure[10403] Entity Framework Core 2.1.1-rtm-30846 initialized 'HelloWorldDBContext' using provider 'Microsoft.EntityFrameworkCore.Sqlite' with options: None 20180623011249_InitialCreate

可以看到總共有一個遷移代碼，那就是 20180623011249_InitialCreate

在解決方案管理器中我們還可以看到多出了一個目錄 Migrations 和多個文件

接下來我們就要開始應用這些遷移來更新數據庫，執行下面的命令來應用遷移代碼

$ dotnet ef database update -v

參數	說明
dotnet	是 .NET 框架所有命令的開始標識
ef	是指使用 Entity Framework 提供的命令
database	是指使用數據庫相關命令
update	是指更新數據庫
-v	參數用於輸出創建遷移代碼時的運行日志，方便出錯時我們可以查看錯在哪里

執行以上命令，輸出結果如下

$ dotnet ef database update -v
Using project '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj'.
Using startup project '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj'. Writing '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/obj/HelloWorld.csproj.EntityFrameworkCore.targets'... dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=/var/folders/yk/2446sljj6hn82nvzkdgxltmw0000gn/T/tmpDJ7JJ2.tmp /verbosity:quiet /nologo /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj Writing '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/obj/HelloWorld.csproj.EntityFrameworkCore.targets'... dotnet msbuild /target:GetEFProjectMetadata /property:EFProjectMetadataFile=/var/folders/yk/2446sljj6hn82nvzkdgxltmw0000gn/T/tmpjmGX4s.tmp /verbosity:quiet /nologo /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj dotnet build /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/HelloWorld.csproj /verbosity:quiet /nologo Build succeeded. 0 Warning(s) 0 Error(s) Time Elapsed 00:00:04.26 dotnet exec --depsfile /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1/HelloWorld.deps.json --additionalprobingpath /Users/yufei/.nuget/packages --additionalprobingpath /usr/local/share/dotnet/sdk/NuGetFallbackFolder --runtimeconfig /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1/HelloWorld.runtimeconfig.json /usr/local/share/dotnet/sdk/2.1.301/DotnetTools/dotnet-ef/2.1.1/tools/netcoreapp2.1/any/tools/netcoreapp2.0/any/ef.dll database update --assembly /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1/HelloWorld.dll --startup-assembly /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1/HelloWorld.dll --project-dir /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/ --language C# --working-dir /Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld --verbose --root-namespace HelloWorld Using assembly 'HelloWorld'. Using startup assembly 'HelloWorld'. Using application base '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/bin/Debug/netcoreapp2.1'. Using working directory '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld'. Using root namespace 'HelloWorld'. Using project directory '/Users/yufei/Developer/aspnetcore/HelloWorld/HelloWorld/'. Finding DbContext classes... Finding IDesignTimeDbContextFactory implementations... Finding application service provider... Finding IWebHost accessor... Using environment 'Development'. Using application service provider from IWebHost accessor on 'Program'. Found DbContext 'HelloWorldDBContext'. Finding DbContext classes in the project... Using context 'HelloWorldDBContext'. info: Microsoft.EntityFrameworkCore.Infrastructure[10403] Entity Framework Core 2.1.1-rtm-30846 initialized 'HelloWorldDBContext' using provider 'Microsoft.EntityFrameworkCore.Sqlite' with options: None Finding design-time services for provider 'Microsoft.EntityFrameworkCore.Sqlite'... Using design-time services from provider 'Microsoft.EntityFrameworkCore.Sqlite'. Finding design-time services referenced by assembly 'HelloWorld'. No referenced design-time services were found. Finding IDesignTimeServices implementations in assembly 'HelloWorld'... No design-time services were found. info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (28ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; Executed DbCommand (28ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (7ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] CREATE TABLE "__EFMigrationsHistory" ( "MigrationId" TEXT NOT NULL CONSTRAINT "PK___EFMigrationsHistory" PRIMARY KEY, "ProductVersion" TEXT NOT NULL ); Executed DbCommand (7ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] CREATE TABLE "__EFMigrationsHistory" ( "MigrationId" TEXT NOT NULL CONSTRAINT "PK___EFMigrationsHistory" PRIMARY KEY, "ProductVersion" TEXT NOT NULL ); info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (8ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] SELECT COUNT(*) FROM "sqlite_master" WHERE "name" = '__EFMigrationsHistory' AND "type" = 'table'; Executed DbCommand (8ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] SELECT COUNT(*) FROM "sqlite_master" WHERE "name" = '__EFMigrationsHistory' AND "type" = 'table'; info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] SELECT "MigrationId", "ProductVersion" FROM "__EFMigrationsHistory" ORDER BY "MigrationId"; Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] SELECT "MigrationId", "ProductVersion" FROM "__EFMigrationsHistory" ORDER BY "MigrationId"; info: Microsoft.EntityFrameworkCore.Migrations[20402] Applying migration '20180623011249_InitialCreate'. Applying migration '20180623011249_InitialCreate'. info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; Executed DbCommand (0ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] PRAGMA foreign_keys=ON; info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] CREATE TABLE "Employees" ( "ID" INTEGER NOT NULL CONSTRAINT "PK_Employees" PRIMARY KEY AUTOINCREMENT, "Name" TEXT NULL ); Executed DbCommand (1ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] CREATE TABLE "Employees" ( "ID" INTEGER NOT NULL CONSTRAINT "PK_Employees" PRIMARY KEY AUTOINCREMENT, "Name" TEXT NULL ); info: Microsoft.EntityFrameworkCore.Database.Command[20101] Executed DbCommand (2ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] INSERT INTO "__EFMigrationsHistory" ("MigrationId", "ProductVersion") VALUES ('20180623011249_InitialCreate', '2.1.1-rtm-30846'); Executed DbCommand (2ms) [Parameters=[], CommandType='Text', CommandTimeout='30'] INSERT INTO "__EFMigrationsHistory" ("MigrationId", "ProductVersion") VALUES ('20180623011249_InitialCreate', '2.1.1-rtm-30846'); Done.

輸出日志很長，大概的意思就是執行成功了

應用遷移代碼成功后我們就能在根目錄下發現我們的 blogging.db 文件了

至於它為什么不在前面章節中提到的 bin/Debug 目錄下，我也很疑問，算了，不管了

blogging.db

blogging.db 是一個標准的 SQLite3 數據庫文件，我們可以使用 SQLite Studio 打開看看

對了，SQLite Studio 是一個跨平台的軟件，你可以點擊 https://sqlitestudio.pl/index.rvt?act=download 下載它

使用 SQLite Studio 可以看到我們的 blogging.db 中已經有了表 Employees ，且有兩個字段

本章到這里就結束了，我本來想給大家介紹下遷移代碼的，但這其實已經超出了基礎教程的范疇了，算了，以后有空再來講講

ASP.NET Core 設置和初始化數據庫 - ASP.NET Core 基礎教程 - 簡單教程，簡單編程

初始化數據庫

blogging.db

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