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我有两张表，一张称为 Companies，另一张称为 Locations。Companies 有 Id 和 Name，Locations 有 Id、CompanyId、Name 和 SubAccount。我有两个项目。一种是 IMS.Data，所有验证都在其中，而 IMS 则在 Web 表单页面所在的位置。我无法验证公司是否有位置（如果公司 ID 是任何地方的外键），则不要删除记录。这是我到目前为止所拥有的一切，但我无法引用 Locations CompanyId 以使用 lambda 表达式进行检查。谁能帮助我我是 lambda 表达式的新手。

这是我用于验证的方法

    namespace IMS.Data
{
public class CompanyContext : IMSDBContext
{
    public Company DeleteCompany(Company company)
    {
        if (company.Name == null)
        {
            throw new Exception("Please select a record to delete.");
        }
        if (Companies.Any(x => x.Name == company.Name))
        {
            throw new Exception("Can not delete a company that has a location.");
        }
        Companies.Remove(company);
        return company;
    }

}
}

这是我使用的删除按钮

namespace IMS
{

public partial class CompanySetUp : Page
{
    private const string AddButton = "Add";
    private const string SaveButton = "Save";
    private const string DeleteButton = "Delete";
    private const string CancelButton = "Cancel";

    private int CompanyId // This puts the "CompanyId" into a viewstate and is used to update the record
    {
        get
        {
            return (int)ViewState["_companyId"];
        }
        set
        {
            ViewState["_companyId"] = value;
        }
    }

    private IList<Company> Companies { get; set; } // This gets and sets the list of companies from the table "Companies"

    protected void Page_Load(object sender, EventArgs e)
    {
        PopulateCompanyListGrid();
        //if (Companies != null && Companies.Count > 0) // This will put a record in the "txtCompanyName.Text" on page load
        //{
        //    txtCompanyName.Text = Companies.First().Name;
        //}

    }       

    protected void btnDelete_Click(object sender, EventArgs e) // This will delete the record that matches the textbox or throw an exception
    {
        CompanyContext context = null;
        switch (btnDelete.Text)
        {
            case DeleteButton:
                try
                {
                    context = new CompanyContext();
                    var company = context.Companies.ToList().First(x => x.Name == txtCompanyName.Text);

                    context.DeleteCompany(company);
                    //PopulateCompanyListGrid();
                    Reload();

                }
                catch (Exception ex)
                {
                    lblCompanyNameNotification.Text = ex.Message;
                }
                finally
                {
                    if (context != null)
                    {
                        context.Dispose();
                    }
                }
                PopulateCompanyListGrid();
                break;
            case CancelButton:
                Reload();
                break;
        }
    }
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1 回答 1

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如果您有一个包含此数据和正确设置外键的关系数据库，您可以提交更改并观察SqlExceptionwith code 547，这是一个外键异常。当要删除的数据被其他表引用时，会抛出此错误。

以这种方式处理它的优点是数据存储强制其自身有效，而不是为代码中的所有外键关系定义检查。如果您稍后添加新的 FK，它们将自动由数据库强制执行并被您的代码捕获，而不是您必须向代码本身添加新的检查。

于 2013-08-19T14:39:50.627 回答