[C#.NET][Entity Framework] DbContextTransaction @ EF6
在 ADO.NET 裡的交易機制,在EF6的邏輯基本上一樣,
DbContextTransaction 類別,提供 Commit 認可基礎存放區交易,Rollback 回復基礎存放區交易,兩個方法,
也就是說交易成功調用 Commit,失敗則調用Rollback
假設當我需要將一筆資料同時寫到兩個不同的地方,這時就可以利用 DbContextTransaction 類別 來決定要 Commit,還是Rollback
下面的例子,我故意創建相同的 Id(Primary Key),誘發 DbUpdateException 例外,例外發生則 Rollback
{ using (var localDbContext = new LocalDbContext()) using (var mySqlDbContext = new MySqlDbContext()) using (var transaction1 = localDbContext.Database.BeginTransaction()) using (var transaction2 = mySqlDbContext.Database.BeginTransaction()) { localDbContext.Members.Add(new Member() { Id = 1, Name = "余小章" }); mySqlDbContext.Members.Add(new Member() { Id = 1, Name = "余小章" }); mySqlDbContext.Members.Add(new Member() { Id = 1, Name = "余小章" }); try { var localResult = localDbContext.SaveChanges(); var mySqlResult = mySqlDbContext.SaveChanges(); if (localResult == 0 || mySqlResult == 0) { throw new DbUpdateException(); } transaction1.Commit(); transaction2.Commit(); MessageBox.Show("OK"); } catch (DbUpdateException) { transaction1.Rollback(); transaction2.Rollback(); MessageBox.Show("RollBack"); } } }
這樣一來就能確保雙方資訊一致性,
假設,一次有大量資料需要更新,也可以用它來確保,資料都被全部寫入。
元件版本
<packages> <package id="EntityFramework" version="6.0.0" targetFramework="net45" /> <package id="MySql.Data" version="6.8.3" targetFramework="net45" /> <package id="MySql.Data.Entities" version="6.8.3.0" targetFramework="net45" /> </packages>
組態檔
<configuration> <configSections> <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="v11.0" /> </parameters> </defaultConnectionFactory> <providers> <provider invariantName="MySql.Data.MySqlClient" type="MySql.Data.MySqlClient.MySqlProviderServices, MySql.Data.Entity.EF6"></provider> <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" /> </providers> </entityFramework> <system.data> </system.data> <connectionStrings> <add name="mySql" providerName="MySql.Data.MySqlClient" connectionString="server=localhost; user id=your id; password=your password;database=demo; port=3306" /> <add name="localDb" providerName="System.Data.SqlClient" connectionString="Data Source=(localdb)\v11.0;Initial Catalog=demo;Integrated Security=True" /> </connectionStrings> </configuration>
完整程式碼
public partial class Member { [Key, DatabaseGenerated(DatabaseGeneratedOption.None)] public int Id { get; set; } public string Name { get; set; } public string Phone { get; set; } } [DbConfigurationType(typeof(MySql.Data.Entity.MySqlEFConfiguration))] public class MySqlDbContext : DbContext { public DbSet<Member> Members { get; set; } public MySqlDbContext(string connextStringName) : base(connextStringName) { } public MySqlDbContext() : base("mySql") { } } public class LocalDbContext : DbContext { public DbSet<Member> Members { get; set; } public LocalDbContext() : base("localDb") { } }
在實做這個情境時發現了奇妙的現象
當我先實體化MySQL時,LocalDb居然會套用MySql.Data.MySqlClient…
反過來,就不會有這個現象
但是,資料庫不存在的時候會跳出,Specified key was too long; max key length is 767 bytes 例外訊息
猜測是 MySQL 的 EF 元件有問題,各別單獨運作(不同的Method區塊),則沒有任何問題
文章出自:http://www.dotblogs.com.tw/yc421206/archive/2014/03/20/144457.aspx
文章參考:http://msdn.microsoft.com/en-us/data/dn456843
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