如何以编程方式更改 SQLite DbContext 连接字符串？

Question

如何以编程方式更改 SQLite DbContext 连接字符串？

目标：让用户在应用程序过程中可以通过对话框选择不同的SQLite数据库文件。
如何执行此操作，以便在对话框中选择后，数据库的路径会发生变化。 或者更改 App.config 中的连接字符串。

使用：
Nuget： System.Data.SQLite；
应用程序：控制台。 NET 框架。

我不想安装额外的库..
但如果有需要的话，你可以...

项目 - https://github.com/jhon65496/SqliteConnectStringConslFrmw

方法1
如果你使用这种创建方法

string path = @"C:\Projects\dbAppIndexes3.db";
string connectionString = $"Data Source={path}";
DbContextIndexes dbContextIndexes = new DbContextIndexes(connectionString);

那么代码不会返回任何内容。

方法2
如果你使用这种创作方法。
IE。通过更改 App.config，然后

GetAll1()

工作正常，

GetAll2()

从App.config中读取数据库的路径，路径是之前的路径。

GetAll1();
GetAll2();

packages.config

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="EntityFramework" version="6.4.4" targetFramework="net48" />
  <package id="Stub.System.Data.SQLite.Core.NetFramework" version="1.0.118.0" targetFramework="net48" />
  <package id="System.Data.SQLite" version="1.0.118.0" targetFramework="net48" />
  <package id="System.Data.SQLite.Core" version="1.0.118.0" targetFramework="net48" />
  <package id="System.Data.SQLite.EF6" version="1.0.118.0" targetFramework="net48" />
  <package id="System.Data.SQLite.Linq" version="1.0.118.0" targetFramework="net48" />
</packages>

应用程序配置

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
    <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
  </configSections>
  <startup>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.8" />
  </startup>
    <connectionStrings>
        <add name="DefaultConnection" connectionString="Data Source=dbAppIndexes.db" providerName="System.Data.SQLite" />
    </connectionStrings>
    <entityFramework>
    <providers>
      <provider invariantName="System.Data.SQLite" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6"/>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
      <provider invariantName="System.Data.SQLite.EF6" type="System.Data.SQLite.EF6.SQLiteProviderServices, System.Data.SQLite.EF6" />
    </providers>
  </entityFramework>
  <system.data>
    <DbProviderFactories>
      <remove invariant="System.Data.SQLite.EF6" />
      <add name="SQLite Data Provider (Entity Framework 6)" invariant="System.Data.SQLite.EF6" description=".NET Framework Data Provider for SQLite (Entity Framework 6)" type="System.Data.SQLite.EF6.SQLiteProviderFactory, System.Data.SQLite.EF6" />
    <remove invariant="System.Data.SQLite" /><add name="SQLite Data Provider" invariant="System.Data.SQLite" description=".NET Framework Data Provider for SQLite" type="System.Data.SQLite.SQLiteFactory, System.Data.SQLite" /></DbProviderFactories>
  </system.data>
</configuration>

索引

[Table("Indexes")]
public class Index
{
    public int Id { get; set; }

    public string Name { get; set; }
    
    public string Description { get; set; }        
}

应用服务

class AppService
{
    public AppService()
    {
        
        TestMain();
    }



    public void TestMain()
    {
        // Test 1
        // GetAll();
        
        // Test 2
           GetAll1();
           GetAll2();
    }   

    public void GetAll()
    {
        try
        {
            // 
            // string path = @"C:\Projects\dbAppIndexes3.db";
            // string connectionString = $"Data Source={path}";
            // DbContextIndexes dbContextIndexes = new DbContextIndexes(connectionString);


            // 
            string connectionStringsName = "DefaultConnection2";
            DbContextIndexes dbContextIndexes = new DbContextIndexes(connectionStringsName);

            IndexesRepository indexesRepository = new IndexesRepository(dbContextIndexes);

            var i = indexesRepository.Items.ToArray();
            var indexes = new ObservableCollection<Index>(i);
        }
        catch (Exception ex)
        {
            string s = ex.Message;
            throw;
        }            
    }



    public void GetAll1()
    {
        AppSettingService appSettingService = new AppSettingService();
        
        string path = @"C:\Projects\dbAppIndexes3.db";
        string connectionString = $"Data Source={path}";
        string connectionStringName = @"DefaultConnection";

        appSettingService.SaveConnectionString(connectionStringName, connectionString);
        
        DbContextIndexes dbContextIndexes = new DbContextIndexes(connectionStringName);

        IndexesRepository indexesRepository = new IndexesRepository(dbContextIndexes);

        var i = indexesRepository.Items.ToArray();
        var indexes = new ObservableCollection<Index>(i);
    }

    public void GetAll2()
    {
        AppSettingService appSettingService = new AppSettingService();

        string path = @"C:\Projects\dbAppIndexes4.db";
        string connectionString = $"Data Source={path}";
        string connectionStringName = @"DefaultConnection";

        appSettingService.SaveConnectionString(connectionStringName, connectionString);

        DbContextIndexes dbContextIndexes = new DbContextIndexes(connectionStringName);

        IndexesRepository indexesRepository = new IndexesRepository(dbContextIndexes);

        var i = indexesRepository.Items.ToArray();
        var indexes = new ObservableCollection<Index>(i);
    }


}

索引存储库

class IndexesRepository 
{

    DbContextIndexes _db;
    #region Конструктор --- --- --- ---
    public IndexesRepository(DbContextIndexes db)
    {
        _db = db;
    }

    #endregion

    public IQueryable<Index> Items => _db.Indexes;

}

DbContextIndexes

public class DbContextIndexes : DbContext
{

    public DbContextIndexes() : base("DefaultConnection")
    {

    }

    
    public DbContextIndexes(string connectionStringsName) : base(connectionStringsName)
    {

    }
    
    public DbSet<Index> Indexes { get; set; }        
}

程序.cs

static void Main(string[] args)
{
    // Console.ReadKey();
    AppService appService = new AppService();
}

Answer 1

对于 EF6（.Net Framework），选项 1 应该可以工作，因为您可以向它传递 ConnectionStringName（来自 app.config）或 ConnectionString。但是，如果传递连接字符串，则需要确保它是完整且有效的连接字符串。在您的示例中，您没有传递提供程序，如果您只想使用默认配置的提供程序并覆盖连接字符串，有一个简单的解决方法：

string path = @"C:\Projects\dbAppIndexes3.db";
string connectionString = $"Data Source={path}";

DbContextIndexes dbContextIndexes = new DbContextIndexes(connectionString);

public DbContextIndexes() : base("DefaultConnection")
{ }


public DbContextIndexes(string connectionString) : this () // Use "DefaultConnection" app connection string and provider...
{
    Database.Connection.ConnectionString = connectionString; // Overwrite to use the desired connection string.
}

如果您想支持在不同的提供程序之间进行选择，您可以执行类似的操作，提供提供程序枚举以在连接字符串旁边的 SqlLite、SQL Server 等之间进行选择，然后为每个提供程序创建默认配置，例如 DefaultSqlLiteConnection 和 DefaultSqlServerConnection 等。在配置文件中：

public DbContextIndexes(DbProvider provider, string connectionString)
   : base(provider == DbProvider.SqlServer ? "DefaultSqlServerConnection" : "DefaultSqlLiteConnection")
{
    Database.Connection.ConnectionString = connectionString;
}