如何通过连接字符串创建多个db上下文实例？

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：

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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