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EF6 Create Different DataContext on runtime(运行时改变连接字符串)
引言
在使用EF时，有时我们需要在程序运行过程中动态更改EF的连接字符串，但不幸的时EF是否对
ConfigurationManager.RefreshSection("xxx")
这行代码的影响不大，我没去深究，还请大侠指点。（本人猜测，EF内部实现没有订阅RefreshSection的事件去做相应的更换连接字符串的处理），如果确实想用该方法通过修改配置文件来实现动态更换连接字符串，那最保守的做法再加上个重启应用程序的方法。（确保EF能重新读到新的配置信息。）
这个时候就需要我们在DataContext新建时使用指定DBConnection来解决该问题，Demo如下：
APP.CONFIG (Uses EF 6)
<?xml version="1.0" encoding="utf-8"?><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.SqlConnectionFactory, EntityFramework"> <parameters> <parameter value="Data Source=localhost; Integrated Security=True; MultipleActiveResultSets=True" /> </parameters></defaultConnectionFactory> </entityFramework></configuration>
the code to make as small as possible for Demo:
using System;using System.Data.Common;using System.Data.Entity;using System.Data.Entity.Infrastructure;using System.Data.Entity.Migrations;namespace Ef6Test { public class Program { public static void Main(string[] args) { Database.SetInitializer(new MigrateDatabaseToLatestVersion<Ef6Ctx, Ef6MigConf>()); WhichDb.DbName = "HACKDB1"; var sqlConn = GetSqlConn4DBName(WhichDb.DbName); var context = new Ef6Ctx(sqlConn); context.Database.Initialize(true); AddJunk(context); //sqlConn.Close(); //?? whatever other considerations, dispose of context etc... Database.SetInitializer(new MigrateDatabaseToLatestVersion<Ef6Ctx, Ef6MigConf>()); // yes its default again reset this !!!! WhichDb.DbName = "HACKDB2"; var sqlConn2 = GetSqlConn4DBName(WhichDb.DbName); var context2 = new Ef6Ctx(sqlConn2); context2.Database.Initialize(true); AddJunk(context2); } public static class WhichDb { // used during migration to know which connection to build public static string DbName { get; set; } } private static void AddJunk(DbContext context) { var poco = new pocotest(); poco.f1 = DateTime.Now.ToString(); // poco.f2 = "Did somebody step on a duck?"; //comment in for second run context.Set<pocotest>().Add(poco); context.SaveChanges(); } public static DbConnection GetSqlConn4DBName(string dbName) { var sqlConnFact = new SqlConnectionFactory( "Data Source=localhost; Integrated Security=True; MultipleActiveResultSets=True"); var sqlConn = sqlConnFact.CreateConnection(dbName); return sqlConn; }}public class MigrationsContextFactory : IDbContextFactory<Ef6Ctx> { public Ef6Ctx Create() { var sqlConn = Program.GetSqlConn4DBName(Program.WhichDb.DbName); // NASTY but it works return new Ef6Ctx(sqlConn); }}public class Ef6MigConf : DbMigrationsConfiguration<Ef6Ctx> { public Ef6MigConf() { AutomaticMigrationsEnabled = true; AutomaticMigrationDataLossAllowed = true; }}public class pocotest { public int Id { get; set; } public string f1 { get; set; } // public string f2 { get; set; } // comment in for second run}public class Ef6Ctx : DbContext { public DbSet<pocotest> poco1s { get; set; } public Ef6Ctx(DbConnection dbConn) : base(dbConn, true) { }}}
参考
https://stackoverflow.com/questions/18272708/how-to-force-dbcontext-refresh-connection-string-from-config
https://stackoverflow.com/questions/15504465/entityframework-code-first-custom-connection-string-and-migrations/16133150#16133150
https://github.com/mono/entityframework/blob/master/src/EntityFramework/Infrastructure/SqlConnectionFactory.cs
EF6 Create Different DataContext on runtime(运行时改变连接字符串)
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