How Can I Dynamically Change Entity Framework Connection Strings in a Web API?

Entity Framework: Dynamic Operation Connection

Your Web API project allows users to select a different database when logging in. This involves dynamically updating the Entity Framework connection string. Here's how to achieve this:

Change connection

To change the data context connection, you can modify the connection string of the underlying SqlConnection. The SqlConnectionStringBuilder class provides a convenient way to build connection strings.

<code class="language-csharp">public void Connect(Database database)
{
    // 构建 SQL 连接字符串
    SqlConnectionStringBuilder sqlString = new SqlConnectionStringBuilder()
    {
        DataSource = database.Server,
        InitialCatalog = database.Catalog,
        UserID = database.Username,
        Password = database.Password,
    };

    // 构建 Entity Framework 连接字符串
    EntityConnectionStringBuilder entityString = new EntityConnectionStringBuilder()
    {
        Provider = database.Provider,
        Metadata = Settings.Default.Metadata,
        ProviderConnectionString = sqlString.ToString()
    };

    // 更新数据上下文的连接
    using (var context = new MyDbContext(entityString.ConnectionString))
    {
        // 执行数据库操作
    }
}</code>

Connection persistence

In Web API projects, connections should not persist across the user's entire session. Each request should pass its own connection string to the data context. This ensures security and prevents potential database conflicts. You can store the connection string in the session or pass it as a parameter to the API call.

Extension methods

Another approach is to use an extension method that automatically performs the join operation. The following code demonstrates how to achieve this:

<code class="language-csharp">public static class ConnectionTools
{
    public static void ChangeDatabase(this DbContext source, string initialCatalog, string dataSource, ...)
    {
        try
        {
            var sqlCnxStringBuilder = new SqlConnectionStringBuilder(source.Database.Connection.ConnectionString);
            if (!string.IsNullOrEmpty(initialCatalog)) sqlCnxStringBuilder.InitialCatalog = initialCatalog; // 更新连接字符串参数
            source.Database.Connection.ConnectionString = sqlCnxStringBuilder.ConnectionString;
        }
        catch (Exception ex) { /* 记录或处理异常 */ }
    }
}</code>

You can then conveniently change the connection using this extension method:

<code class="language-csharp">var selectedDb = new MyDbContext();
selectedDb.ChangeDatabase(initialCatalog: "new-catalog");</code>

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