连接字符串-N层应用

Question

I have had a dig around for an answer to this issue but everything previously asked seems to be a complex variation on this and doesn't answer the question so I thought I should just ask.

I am developing a three tier application with the following.....

• DAL - Data Access Layer using Entity Framework
• BLL - Business Logic Layer
• Web App - MVC Web Application

I have created an Entity Framework model, repository classes and my connection string is in the DAL App.Config file. I have now created my first class in the BLL and it references the DAL. When trying to test the following, very basic method I get an error relating to a missing connection string in the BLL.

public static List<DAL.Item> getItems() {

        List<DAL.Item> result = new List<Item>();

        DAL.Repositories.ItemRepository myRepository = new    DAL.Repositories.ItemRepository();
        result = myRepository.GetAll().ToList();

        return result;

    }

Why is the BLL looking for the connection string? Am I missing something really obvious here?

If I need to include the connection string across multiple layers, which defeats the purpose of the n-tier structure, then how is the best way to do this? Can anyone shed some light on this for me?

Answer 1

您正在新建DAL的实例，该实例将尝试查看您的配置文件（由于作用域位于业务层/单元测试中而未找到。您应该做的是查看控制反转（IoC ）并将DAL注入到业务逻辑层中，然后您就可以模拟出不会尝试实际访问配置文件/数据库等的DAL。

Answer 2

原样将连接字符串属性从app.config复制到web.config连接字符串部分...此问题将解决

Answer 3

The connection string should be on your presentation layer (mvc project in your case). Just add the entry on the connectionStrings node in web.config and read it by the System.Configuration on the data layer.

define in web.config a connection string

<connectionStrings>
    <add name="ConnectionStringName" connectionString="Data Source=.\SQLEXPRESS; Database=DataBaseName;..." providerName="System.Data.SqlClient" />
</connectionStrings>

in your DataContext of Entity-Framework you can pass the key in the web.config file

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext()
        : base("ConnectionStringName")
    {
    }

    // DbSet properties...
}

To read from configuration file and take a string you have to add a reference for System.Configuration assembly and try this:

using System.Configuration;

string connectionString = ConfigurationManager.ConnectionStrings["connectionStringName"].ConnectionString;