如何通过连接字符串创建多个db上下文实例？ [英] How create multiple db context instances by connecting strings?

问题描述

在C＃中，MVC代码第一个应用程序我有

In C#, MVC code first application I have

public class CarContext : DbContext { }

class 。连接字符串就像

class in first version of application. And connection string is like

<add name="CarContext" providerName="System.Data.SqlClient" Integrated Security=true;
connectionString="Data Source=Dragon; Initial Catalog=CarDBv1;"/>

当我运行应用程序时，首先创建数据库版本 - CarDBv1 。

When I run application, first version of database is created - CarDBv1.

然后我编辑我的CarContext类，例如添加新表，更改任何属性等，还可以更改应用程序的版本，更改连接字符串

Then I edit my CarContext class, for example, add new table, change any property etc., also change version of application, change connection string

初始目录= CarDBv1; 至初始目录= CarDBv2; 并运行项目。在这种情况下，我有2个数据库： CarDBv1 和 CarDBv2 。但是，CarContext类在应用程序中是相同的。

Initial Catalog=CarDBv1; to Initial Catalog=CarDBv2; and run project. In this case I have 2 database: CarDBv1 and CarDBv2. But, CarContext class is same in applications.

现在，我需要从任何控制台应用程序连接数据库及其上下文（CarContext），并使用它们的表进行转换，阅读等等。

Now, I need to connect both database and their context(CarContext) from any console application and use their tables for converting, reading etc.

我在这里找到了类似的答案： https：// stackoverflow。 com / a / 16860878/1534785

I found a similar answer here: https://stackoverflow.com/a/16860878/1534785

但在我的应用程序上下文名称相同。

But in my applications context name is same.

如何通过数据库连接字符串为应用程序中的每个CarContext创建2个实例？

How can I create 2 instances for every CarContext in applications by their database connection string?

推荐答案

可以使用重载的构造函数DbContext允许上下文指向和任意数据库，这是在app.config中未声明的。
请参阅使用dbConnection的构造函数。

You can use an overloaded constructor to DbContext to allow contexts to point at and arbitrary database which is NOT declared in app.config. See the constructor with dbConnection.

public  class MyDbContext : DbContext, IContextOptions  {
    //ctors
    protected BosBaseDbContext(string connectionName)
        : base(connectionName) {          }

    protected BosBaseDbContext(DbConnection dbConnection, bool contextOwnsConnection)
        : base(dbConnection, contextOwnsConnection) {       }

}

使用

//datasource could be localhost, DBName the catalog name 
new MyDbContext((GetSqlConn4DbName(dataSource,dbName )),true);  


 public DbConnection GetSqlConn4DbName(string dataSource, string dbName) {
        var sqlConnStringBuilder = new SqlConnectionStringBuilder();
        sqlConnStringBuilder.DataSource = String.IsNullOrEmpty(dataSource) ? DefaultDataSource : dataSource;
        sqlConnStringBuilder.IntegratedSecurity = true;
        sqlConnStringBuilder.MultipleActiveResultSets = true;

        var sqlConnFact = new SqlConnectionFactory(sqlConnStringBuilder.ConnectionString);
        var sqlConn = sqlConnFact.CreateConnection(dbName);
        return sqlConn;
    }

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