在运行时的实体框架连接的变化 [英] Entity Framework change connection at runtime

问题描述

我有一个Web API项目，引用我的模型和DAL组件。用户被presented一个登录屏幕，在那里他可以选择不同的数据库。

I have a web api project which references my model and DAL assemblies. The user is presented with a login screen, where he can select different databases.

我建立的连接字符串如下：

I build the connection string as follows:

    public void Connect(Database database)
    {
        //Build an SQL connection string
        SqlConnectionStringBuilder sqlString = new SqlConnectionStringBuilder()
        {
            DataSource = database.Server,
            InitialCatalog = database.Catalog,
            UserID = database.Username,
            Password = database.Password,
        };

        //Build an entity framework connection string
        EntityConnectionStringBuilder entityString = new EntityConnectionStringBuilder()
        {
            Provider = database.Provider,
            Metadata = Settings.Default.Metadata,
            ProviderConnectionString = sqlString.ToString()
        };
    }

首先，我如何真正改变dataconext的连接？

First of all, how do I actually change the connection of the dataconext?

其次，因为这是一个Web API项目，是的ConnectionString（设置为每以上登录）持续整个用户交互，还是应该被传递到每次我的DataContext？

And secondly, as this is a web api project, is the connectionstring (set at login per above) persistent throughout the user's interaction or should it be passed everytime to my datacontext?

推荐答案

一个有点晚对这个答案，但我觉得有一个整洁的小扩展方法来做到这一点的潜在方法。我们可以利用EF约定优于配置再加上一些微架构的呼叫。

A bit late on this answer but I think there's a potential way to do this with a neat little extension method. We can take advantage of the EF convention over configuration plus a few little framework calls.

反正评论code和用法示例：

Anyway, the commented code and example usage:

扩展方法类：

public static class ConnectionTools
{
    // all params are optional
    public static void ChangeDatabase(
        this DbContext source,
        string initialCatalog = "",
        string dataSource = "",
        string userId = "",
        string password = "",
        bool integratedSecuity = true,
        string configConnectionStringName = "") 
        /* this would be used if the
        *  connectionString name varied from 
        *  the base EF class name */
    {
        try
        {
            // use the const name if it's not null, otherwise
            // using the convention of connection string = EF contextname
            // grab the type name and we're done
            var configNameEf = string.IsNullOrEmpty(configConnectionStringName)
                ? source.GetType().Name 
                : configConnectionStringName;

            // add a reference to System.Configuration
            var entityCnxStringBuilder = new EntityConnectionStringBuilder
                (System.Configuration.ConfigurationManager
                    .ConnectionStrings[configNameEf].ConnectionString);

            // init the sqlbuilder with the full EF connectionstring cargo
            var sqlCnxStringBuilder = new SqlConnectionStringBuilder
                (entityCnxStringBuilder.ProviderConnectionString);

            // only populate parameters with values if added
            if (!string.IsNullOrEmpty(initialCatalog))
                sqlCnxStringBuilder.InitialCatalog = initialCatalog;
            if (!string.IsNullOrEmpty(dataSource))
                sqlCnxStringBuilder.DataSource = dataSource;
            if (!string.IsNullOrEmpty(userId))
                sqlCnxStringBuilder.UserID = userId;
            if (!string.IsNullOrEmpty(password))
                sqlCnxStringBuilder.Password = password;

            // set the integrated security status
            sqlCnxStringBuilder.IntegratedSecurity = integratedSecuity;

            // now flip the properties that were changed
            source.Database.Connection.ConnectionString 
                = sqlCnxStringBuilder.ConnectionString;
        }
        catch (Exception ex)
        {
            // set log item if required
        }
    }
}

基本用法：

// assumes a connectionString name in .config of MyDbEntities
var selectedDb = new MyDbEntities();
// so only reference the changed properties
// using the object parameters by name
selectedDb.ChangeDatabase
    (
        initialCatalog: "name-of-another-initialcatalog",
        userId: "jackthelady",
        password: "nomoresecrets",
        dataSource: @".\sqlexpress" // could be ip address 120.273.435.167 etc
    );

我知道你已经有到位的基本功能，但认为这将增加一点多样性。

I know you already have the basic functionality in place, but thought this would add a little diversity.

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