c# - DbContext 不释放 SQLite 数据库

Question

首先，这些是我的意图:

1. 在 SQLite 上创建一个 DbContext
2. 对其读写
3. 关闭上下文
4. 将文件移动到另一个位置

第 1-3 点非常有效。当我尝试移动数据库时，问题就开始了。我收到一条错误消息:

'The process cannot access the file because it is being used by another process.' 

我该如何解决？

首先，我创建了一个上下文。我必须以多种方式使用它，而且我不想每次需要它时都创建它。所以我将其存储为成员。

_sqliteContext = new SqlLiteContext(sqliteContextName);

然后我想访问一个名为 sync 的表并获取其最新条目。

var sync = _sqliteContext.Syncs.OrderByDescending(s => s.Date);
_lastSync = sync.Any() ? sync.First().Date : new DateTime(0);

就是这样。然后我关闭上下文。

_sqliteContext.Dispose();

并尝试移动文件。

File.Move(sqliteUploadLocation, sqliteDownloadLocation);

这是我得到异常的地方。

当我用插入替换选择时，如下所示:

var sync = new Sync { Id = Guid.NewGuid().ToString(), Date = DateTime.Now };
_sqliteContext.Syncs.Add(sync);
_sqliteContext.SaveChanges();

这行得通，我可以移动数据库。为什么我的选择没有释放它的锁有什么想法吗？

更新

---

// Start synchronisation.
new SyncManager(mssqlString, sqliteUploadLocation).Start();

// Move file from upload to download location.
try
{
    File.Move(sqliteUploadLocation, sqliteDownloadLocation);
}
catch (Exception ex)
{
    Console.WriteLine("Moving failed!");
    Console.WriteLine(ex.Message);
}

public void Start()
{
    // Create connection string for the sqlite database.
    const string sqliteContextName = "SqLiteContext";
    var sqliteConnStringSettings = new ConnectionStringSettings
        {
            Name = sqliteContextName,
            ConnectionString = "Data Source=" + _sqliteUploadLocation + ";Version=3;BinaryGUID=False;",
            ProviderName = "System.Data.SQLite"
        };

    // Read configuration, delete available connection strings and add ours.
    var conf = ConfigurationManager.OpenMachineConfiguration();
    var connStrings = conf.ConnectionStrings;
    connStrings.ConnectionStrings.Remove(sqliteContextName);
    connStrings.ConnectionStrings.Add(sqliteConnStringSettings);
    try
    {
        conf.Save(ConfigurationSaveMode.Minimal);
    }
    catch (Exception)
    {
        // Insufficient rights to save.
        return;
    }

    ConfigurationManager.RefreshSection("connectionStrings");

    // Create connection to the sqlite database.
    _sqliteContext = new SqlLiteContext(sqliteContextName);

    // Create connection to the mssql database.
    _mssqlContext = new MsSqlContext(_mssqlConnString);

    // Read last sync date.
    var sync = _sqliteContext.Syncs.OrderByDescending(s => s.Date);
    _lastSync = sync.Any() ? sync.First().Date : new DateTime(0);

    // Synchronize tables.
    //SyncTablePerson();
    //SyncTableAddressAllocation();

    // Creates an entry for this synchronisation.
    CreateSyncEntry();

    // Release resources.
    _sqliteContext.Dispose();
    _mssqlContext.Dispose();
}

private void CreateSyncEntry()
{
    var sync = new Sync { Id = Guid.NewGuid().ToString(), Date = DateTime.Now };
    _sqliteContext.Syncs.Add(sync);
    _sqliteContext.SaveChanges();
}

更新 2

---

public class SqlLiteContext : Context
{
    public DbSet<Sync> Syncs { get; set; }

    public SqlLiteContext(string connectionString)
        : base(connectionString)
    {
        Database.SetInitializer(new NoOperationStrategy<SqlLiteContext>());
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new PersonConfig());
        modelBuilder.Configurations.Add(new AddressAllocationConfig());
        modelBuilder.Configurations.Add(new AddressConfig());
        modelBuilder.Configurations.Add(new SyncConfig());
    }
}

public class NoOperationStrategy<T> : IDatabaseInitializer<T> where T : DbContext
{
    public void InitializeDatabase(T context)
    {
    }
}

public abstract class Context : DbContext
{
    public DbSet<Person> Persons { get; set; }
    public DbSet<AddressAllocation> AddressAllocations { get; set; }
    public DbSet<Address> Addresses { get; set; }

    protected Context(string connectionString)
        : base(connectionString)
    {
    }
}

使用重构

---

using (var sqliteContext = new SqlLiteContext(_sqliteContextName))
{
    // Read last sync date.
    var sync = sqliteContext.Syncs.Select(s => s).OrderByDescending(s => s.Date);
    var lastSync = sync.Any() ? sync.First().Date : new DateTime(1900, 1, 1);

    using (var mssqlContext = new MsSqlContext(_mssqlConnString))
    {
        SyncTablePerson(sqliteContext, mssqlContext, lastSync);
        SyncTableAddressAllocation(sqliteContext, mssqlContext, lastSync);

        // Save server changes.
        mssqlContext.SaveChanges();
    }

    // Creates an entry for this synchronisation.
    sqliteContext.Syncs.Add(new Sync { Id = Guid.NewGuid().ToString(), Date = DateTime.Now });

    // Save local changes.
    sqliteContext.SaveChanges();
}

Answer 1

我想到了两件事:

1. 确保 Visual Studio 没有锁定数据库文件。打开服务器资源管理器，如果存在与该文件的连接，请确保其已关闭或完全删除。
2. 很可能是连接池使连接保持打开状态。像这样在连接字符串中禁用池:

Data Source=e:\mydb.db;Version=3;Pooling=False;

正如 Matt 指出的那样，您应该真正使用 using 语句而不是手动调用 dispose。这样，如果出现异常，资源总是会被正确释放。