Entity Framework Code First 資料庫初始化設定

Oct 31, 2014

6 mins read

Code First Entity Framework
Code first Entity framework

在參考了entityFramework套件之後，設定檔中會自動增加一個EntityFramework的區域設定 其中的defaultConnectionFactory宣告了預設的資料庫位置 不同的版本預設的localdb實體名稱會有不同，這邊的例子是mssqllocaldb

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <configSections>
        <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
        <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
    </configSections>
    <startup>
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
    <entityFramework>
        <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
            <parameters>
                <parameter value="mssqllocaldb" />
            </parameters>
        </defaultConnectionFactory>
        <providers>
            <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
        </providers>
    </entityFramework>
</configuration>
就會自動建立一個包含完整Assembly名稱的資料庫
[![](http://3.bp.blogspot.com/-u6i3p3OnimM/VFNEtuySOlI/AAAAAAAABtk/lDxVN9zSfD8/s1600/db.png)](http://3.bp.blogspot.com/-u6i3p3OnimM/VFNEtuySOlI/AAAAAAAABtk/lDxVN9zSfD8/s1600/db.png)

如果在設定檔的連線區段中，有一個和DbContext同名的設定值，就會改用這邊的連線設定 建立的資料庫也會是連線字串中指定的名稱

<connectionStrings>
    <add name="DemoContext" providerName="System.Data.SqlClient"
            connectionString="Data Source=(localdb)\v11.0;Initial Catalog=Demo;Integrated Security=true;"/>
</connectionStrings>
[![](http://2.bp.blogspot.com/-B1iIDWV-srg/VFNGwAUTTXI/AAAAAAAABt4/eI2Gmbx2deY/s1600/02.%E9%80%A3%E7%B7%9A%E5%AD%97%E4%B8%B2.png)](http://2.bp.blogspot.com/-B1iIDWV-srg/VFNGwAUTTXI/AAAAAAAABt4/eI2Gmbx2deY/s1600/02.%E9%80%A3%E7%B7%9A%E5%AD%97%E4%B8%B2.png)
也可以透過預設建構式指定要使用設定檔中的那個值 
<connectionStrings>
    <add name="DemoContext" providerName="System.Data.SqlClient"
            connectionString="Data Source=(localdb)\v11.0;Initial Catalog=Demo;Integrated Security=true;"/>
    <add name="d1" providerName="System.Data.SqlClient"
            connectionString="Data Source=(localdb)\v11.0;Initial Catalog=d1;Integrated Security=true;"/>
</connectionStrings>

public class DemoContext : DbContext
{
    public DemoContext() : base("name=d1")
    {
    }

public DbSet&lt;Class1&gt; Class1 { get; set; }



}
或是使用DbContext物件時，透過建構式傳入要使用的名稱

<connectionStrings>
    <add name="DemoContext" providerName="System.Data.SqlClient"
            connectionString="Data Source=(localdb)\v11.0;Initial Catalog=Demo;Integrated Security=true;"/>
    <add name="d1" providerName="System.Data.SqlClient"
            connectionString="Data Source=(localdb)\v11.0;Initial Catalog=d1;Integrated Security=true;"/>
    <add name="d2" providerName="System.Data.SqlClient"
                connectionString="Data Source=(localdb)\v11.0;Initial Catalog=d2;Integrated Security=true;"/>
</connectionStrings>
public class DemoContext : DbContext
{
    public DemoContext() : base("name=d1")
    {
    }

public DemoContext(string name) : base(name)
{
}

public DbSet&lt;Class1&gt; Class1 { get; set; }



}

static void Main(string[] args)
{
    using (DemoContext db = new DemoContext("d2"))
    {
        db.Database.Initialize(true);
    }
}
[![](http://3.bp.blogspot.com/-BhpDZY3FCIc/VFNLSgDVLuI/AAAAAAAABuk/GA9qeZJMc00/s1600/d2.png)](http://3.bp.blogspot.com/-BhpDZY3FCIc/VFNLSgDVLuI/AAAAAAAABuk/GA9qeZJMc00/s1600/d2.png)
另一種建構式是傳入DbConnection物件，搭配contextOwnsConnection來決定是否要共用連線 
public class DemoContext : DbContext
{
    public DemoContext() : base("name=d1")
    {
    }

public DemoContext(string name) : base(name)
{
}

public DemoContext(DbConnection connection) : base(connection, contextOwnsConnection: false)
{
}

public DbSet&lt;Class1&gt; Class1 { get; set; }



}
如果共用連線的話，在第一個DbContext執行完後就會釋放連線 執行第二個DbContext物件的時後就會報錯

static void Main(string[] args)
{
    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["d1"].ConnectionString);

using (DemoContext db = new DemoContext(conn))
{
    Console.WriteLine(db.Class1.Count());
}

using (DemoContext db = new DemoContext(conn))
{
    Console.WriteLine(db.Class1.Count());
}



}
System.Data.Entity.Database.SetInitializer函式可以用來初始化資料庫 System.Data.Entity.CreateDatabaseIfNotExists 只有在資料庫不存在的時後才會建立，這是預設的策略

System.Data.Entity.DropCreateDatabaseIfModelChanges 只有當資料庫結構發生變化的時後，才砍掉重練

System.Data.Entity.DropCreateDatabaseAlways 不管資料庫結構是否有改變，每次都砍掉重練

通常在應用程式的進入點例如Global.asax，Main會設置初始化策略 但是在切換環境的時後，要改變策略就要重新修改編譯部署 所以比較方便的方式，是配置在設定檔中，有兩種設定方式

一種是設定在AppSetting區段，設成Disabled就是禁用資料庫初始化功能

<appSettings>
    <add key="DatabaseInitializerForType ConsoleApplication1.Models.DemoContext, ConsoleApplication1"
            value="System.Data.Entity.DropCreateDatabaseIfModelChanges`1[[ConsoleApplication1.Models.DemoContext, ConsoleApplication1]], EntityFramework" />
    <!--<add key="DatabaseInitializerForType ConsoleApplication1.Models.DemoContext, ConsoleApplication1"
            value="Disabled" />-->
</appSettings>
一種是設定在entityFramework的contextx區段 
<entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
        <parameters>
            <parameter value="mssqllocaldb" />
        </parameters>
    </defaultConnectionFactory>
    <contexts>
        <context type="ConsoleApplication1.Models.DemoContext, ConsoleApplication1">
            <databaseInitializer type="System.Data.Entity.DropCreateDatabaseIfModelChanges`1[[ConsoleApplication1.Models.DemoContext, ConsoleApplication1]], EntityFramework" />
        </context>
    </contexts>
    <providers>
        <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
</entityFramework>
最後可以新增一個自訂的策略，並覆寫Seed函式，就能在初始化資料庫的時後，執行自訂的動作，例如新增資料 
public class MyInitialize : DropCreateDatabaseIfModelChanges<DemoContext>
{
    protected override void Seed(DemoContext context)
    {
        context.Class1.Add(new Class1 { C1 = "a" });
        context.Class1.Add(new Class1 { C1 = "b" });
        context.Class1.Add(new Class1 { C1 = "c" });
    }
}

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