Question

我是实体框架的新手，我对在一个方法调用另一个方法时处理我的DbContext的正确方法感到困惑。这些都是独立调用的，这就是DeleteSheet是独立的原因。但是，当删除父（Chain）时，DeleteChain调用DeleteSheet删除子项。

我尝试在每个方法中处理，但是当我运行DeleteChain时，我得到：

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

在

db.Chains.Remove(chain);

我猜它是因为我在移除孩子时在DeleteSheet中处理了它。

以下是我的方法：

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，因为如果我只处理DeleteChain然后在DeleteChain之外调用DeleteSheet，它就不会被处置。

编辑：尝试＃2。我将每个包装在一个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了，并在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. db.SaveChanges() DeleteChain上投了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(); } }。 / p>

尝试＃2。

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

一样使用它

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，您可以确保仅在完成所有删除后才处理上下文。我总是试图避免一次使用多个上下文，我之前已经被它严重烧伤了！

Answer 4

在您的设计中，ControllerHelper是UranusContext的组合。这意味着您设计的只要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

通过将其作为一个合成，您可以向您的班级用户承诺，只要您的班级存在，您的所有功能都会起作用。因此，在用户通知您不再需要您的功能之前，您不应Dispose() UranusContext任何功能。这可以通过制作ControllerHelper IDisposable

来完成

如果任何类实现了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()。

在您的情况下，代码将是：

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
    }
}

用法是：

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

当一个方法调用另一个方法并且都使用DbContext时，正确处理DbContext的方法

4 个答案: