当一种方法调用另一种方法并且都使用 DbContext 时处理 DbContext 的正确方法

Question

我是 Entity Framework 的新手，当一种方法调用另一种方法时，我对处置我的 DbContext 的正确方法感到困惑。这两个都被独立调用，这就是 DeleteSheet 是独立的原因。但是，当父（链）被删除时，DeleteChain 调用 DeleteSheet 来删除子。

我尝试在每种方法中处理，但是当我运行 DeleteChain 时，我得到：

The operation cannot be completed because the DbContext has been disposed.

开

db.Chains.Remove(chain);

我猜是因为我在删除子项时在 DeleteSheet 中处理了它。

这是我的方法：

public class ControllerHelper
{
    private UranusContext db = new UranusContext();

    public void DeleteChain(int? chainId)
    {
        var chain = db.Chains.Include(c => c.Sheets)
            .SingleOrDefault(c => c.ChainId == chainId);

        // Removes sheets (children)
        foreach (var sheet in chain.Sheets.ToList())
        {
            DeleteSheet(sheet.SheetId);
        }

        db.Chains.Remove(chain);
        db.SaveChanges();
        db.Dispose();
    }

    public void DeleteSheet(int? sheetId)
    {
        var sheet = db.Sheets.Include(s => s.FileDetails)
            .Include(s => s.SheetsCounties)
            .SingleOrDefault(s => s.SheetId == sheetId);

        foreach (var fileDetails in sheet.FileDetails.ToList())
        {
            db.FileDetails.Remove(fileDetails);
        }

        foreach (var sheetsCounties in sheet.SheetsCounties.ToList())
        {
            db.SheetsCounties.Remove(sheetsCounties);
        }

        db.Sheets.Remove(sheet);
        db.SaveChanges();

        db.Dispose();
    }
}

在这种情况下如何正确处理 DbContext？我很困惑，因为如果我只在 DeleteChain 中处理，然后在 DeleteChain 之外调用 DeleteSheet，它就不会处理。

编辑：尝试 #2。我将每个包装在使用中并单独处理它们。但是，当我删除 DeleteSheet 中的孩子时，DeleteChain 并没有意识到我这样做并抛出：The operation failed: The relationship could not be changed because one or more of the foreign-key properties is non-nullable. When a change is made to a relationship, the related foreign-key property is set to a null value. If the foreign-key does not support null values, a new relationship must be defined, the foreign-key property must be assigned another non-null value, or the unrelated object must be deleted. on db.SaveChanges() in DeleteChain。

尝试 #2。

public void DeleteChain(int? chainId)
{
    using (UranusContext db = new UranusContext())
    {
        var chain = db.Chains.Include(c => c.Sheets)
            .SingleOrDefault(c => c.ChainId == chainId);

        // Removes sheets (children)
        foreach (var sheet in chain.Sheets.ToList())
        {
            DeleteSheet(sheet.SheetId);
            //db.Sheets.Remove(sheet);
        }

        db.Chains.Remove(chain);
        db.SaveChanges();
    }
}

public void DeleteSheet(int? sheetId)
{
    using (UranusContext db = new UranusContext())
    {
        var sheet = db.Sheets.Include(s => s.FileDetails)
            .Include(s => s.SheetsCounties)
            .SingleOrDefault(s => s.SheetId == sheetId);

        foreach (var fileDetails in sheet.FileDetails.ToList())
        {
            db.FileDetails.Remove(fileDetails);
        }

        foreach (var sheetsCounties in sheet.SheetsCounties.ToList())
        {
            db.SheetsCounties.Remove(sheetsCounties);
        }

        db.Sheets.Remove(sheet);
        db.SaveChanges();
    }
}

Answer 1

您可能希望在单独的方法中移动工作表删除逻辑，并从 DeleteChain 和 DeleteSheet 中调用它，如下所示：

public class ControllerHelper
{
    public void DeleteChain(int? chainId) {
        using (var db = new UranusContext()) {
            var chain = db.Chains.Include(c => c.Sheets)
                .SingleOrDefault(c => c.ChainId == chainId);

            // Removes sheets (children)
            foreach (var sheet in chain.Sheets.ToList()) {
                DeleteSheet(db, sheet);
            }

            db.Chains.Remove(chain);
            db.SaveChanges();
        }
    }

    public void DeleteSheet(int? sheetId) {
        using (var db = new UranusContext()) {
            var sheet = db.Sheets.Include(s => s.FileDetails)
                .Include(s => s.SheetsCounties)
                .SingleOrDefault(s => s.SheetId == sheetId);

            DeleteSheet(db, sheet);
            db.SaveChanges();
        }
    }

    private void DeleteSheet(UranusContext db, Sheet sheet) {
        foreach (var fileDetails in sheet.FileDetails.ToList()) {
            db.FileDetails.Remove(fileDetails);
        }

        foreach (var sheetsCounties in sheet.SheetsCounties.ToList()) {
            db.SheetsCounties.Remove(sheetsCounties);
        }

        db.Sheets.Remove(sheet);
    }
}

Answer 2

最简单的方法是将 DbContext 作为参数传递：

public class ControllerHelper
{
    public void DeleteChain(int? chainId, UranusContext db)
    {
        var chain = db.Chains.Include(c => c.Sheets)
            .SingleOrDefault(c => c.ChainId == chainId);

        // Removes sheets (children)
        foreach (var sheet in chain.Sheets.ToList())
        {
            DeleteSheet(sheet.SheetId, db);
        }

        db.Chains.Remove(chain);
    }

    public void DeleteSheet(int? sheetId, UranusContext db)
    {
        var sheet = db.Sheets.Include(s => s.FileDetails)
            .Include(s => s.SheetsCounties)
            .SingleOrDefault(s => s.SheetId == sheetId);

        foreach (var fileDetails in sheet.FileDetails.ToList())
        {
            db.FileDetails.Remove(fileDetails);
        }

        foreach (var sheetsCounties in sheet.SheetsCounties.ToList())
        {
            db.SheetsCounties.Remove(sheetsCounties);
        }

        db.Sheets.Remove(sheet);
    }
}

然后像这样使用它

public void Foo(int? someChainId, int? someSheetId, bool required = false)
{
    ControllerHelper hlp = new ControllerHelper();
    using (UranusContext db = new UranusContext())
    {
        hlp.DeleteChain(someChainId);

        if(_required)
            hlp.DeleteSheet(int? someSheetId);

        db.SaveChanges();
    }
}

Answer 3

尝试使用模式并将上下文作为参数传递给 DeleteSheet 方法：

    public class ControllerHelper
{
    public void DeleteChain(int? chainId)
    {
    using (UranusContext db = new UranusContext())
    {
            var chain = db.Chains.Include(c => c.Sheets)
                .SingleOrDefault(c => c.ChainId == chainId);

            // Removes sheets (children)
            foreach (var sheet in chain.Sheets.ToList())
            {
                DeleteSheet(sheet.SheetId, db);
            }

            db.Chains.Remove(chain);
            db.SaveChanges();
    }
    }

    public void DeleteSheet(int? sheetId, UranusContext db)
    {
        var sheet = db.Sheets.Include(s => s.FileDetails)
            .Include(s => s.SheetsCounties)
            .SingleOrDefault(s => s.SheetId == sheetId);

        foreach (var fileDetails in sheet.FileDetails.ToList())
        {
            db.FileDetails.Remove(fileDetails);
        }

        foreach (var sheetsCounties in sheet.SheetsCounties.ToList())
        {
            db.SheetsCounties.Remove(sheetsCounties);
        }

        db.Sheets.Remove(sheet);
        db.SaveChanges();
    }
}

这样，您可以确保只有在所有删除都完成后才会释放上下文。我总是尽量避免一次使用多个上下文，我以前被这种情况严重烧伤！

Answer 4

在您的设计中，ControllerHelper 是 UranusContext 的组合。这意味着您设计了只要ControllerHelper 存在，UranusContext 就存在，并且您希望UranusCibtext 在ControllerHelper 不再存在时立即停止存在。

通过使它成为一个组合，你向你的类的用户保证，只要你的类存在，你的所有函数都可以工作。因此，在您的用户通知您他们不再需要您的功能之前，您不应该在您的任何功能中使用Dispose() UranusContext。这可以通过使您的ControllerHelper IDisposable 来完成

如果有任何类实现了 IDisposable，则此类的设计者鼓励用户在不再需要该对象的功能后尽快调用Dispose()。

在你的情况下，代码是：

public class ControllerHelper : IDisposable()
{
    private UranusContext db = new UranusContext();

    public void Dispose()
    {
        if (this.db != null)
        {
            this.db.Dispose();
            this.db = null;
        }
        GC.SuppressFinalize(this);
    }

    public void DeleteChain(int? chainId)
    {
       // Do what you need to do, but don't Dispose()
       // nor use using, we want db to be functional
    }
    public void DeleteSheet(int? sheetId)
    {
       // Do what you need to do, but don't Dispose()
       // nor use using, we want db to be functional
    }
}

用法如下：

using (var controllerHelper = new ControllerHelper())
{
    // call functions from controllerhelper
}
// the controllerHelper is not needed anymore, Dispose() is called automatically
// and thus db is Disposed