在绑定组合框中空空项目 [英] NULL Empty Item in Bound ComboBox

问题描述

我怎么可以在绑定组合框，它使用 NULL 作为一个插入值或空项更新？

通过下面的code，我可以手动添加其他行。列 inspector_id 是一个FK关系的主键。我必须设置 inspector_id = -1 ，因为C＃不允许的 INT 是空。然而，插入（或更新）失败，因为没有 inspector_id：-1 数据库

 私人无效ItemInfo_Load（对象发件人，EventArgs的）
{
    // TODO：这行code加载数据到someDBDataSet.inspector'表。您可以移动，或将其删除，因为需要的。
    this.inspectorTableAdapter.ClearBeforeFill = FALSE;
    someDBDataSet.inspectorRow NEWROW = this.someDBDataSet.inspector.NewinspectorRow（）;
    newRow.inspector_id = -1; //由于在C＃中int类型不能为空
    newRow.fullName =（无）;
    newRow.employee code =;
    this.someDBDataSet.inspector.AddinspectorRow（NEWROW）;

    this.inspectorTableAdapter.Fill（this.someDBDataSet.inspector）;
    //this.inspectorTableAdapter.ClearBeforeFill = FALSE;
    // TODO：这行code加载数据到someDBDataSet.item'表。您可以移动，或将其删除，因为需要的。
    this.itemTableAdapter.Fill（this.someDBDataSet.item）;
}
 

解决方案

尤里卡！绑定到一个视图，而不是表。

绑定 inspector_idComboBox 的检查表中的一个新的SQL Server视图。

  SELECT NULL作为inspector_id，（无）作为全名，为员工code
联盟
SELECT inspector_id，全名，员工code
从dbo.inspector
 

优点：

1. 的（无）产品在组合框
在选择项目时
2. 的的SelectedItem 和文本仍然存在。
3. 在SQL视图允许空值 inspector_id
4. 没有解决方法都需要在应用程序code。只需填写数据集从视图。
5. 允许更多的灵活性，由于工作的关系未绑定。

...辉煌！

How can I have an empty item in the bound ComboBox which uses NULL as the value for an Insert or Update?

With the code below, I can manually add the additional row. The column inspector_id is the primary key of an FK relationship. I have to set inspector_id = -1, since C# does not allow an int to be null. However, the insert (or update) fails since there is no inspector_id: -1 in the database.

private void ItemInfo_Load(object sender, EventArgs e)
{
    // TODO: This line of code loads data into the 'someDBDataSet.inspector' table. You can move, or remove it, as needed.
    this.inspectorTableAdapter.ClearBeforeFill = false;
    someDBDataSet.inspectorRow newRow = this.someDBDataSet.inspector.NewinspectorRow();
    newRow.inspector_id = -1; // Since an int in C# cannot be null
    newRow.fullName = "(none)";
    newRow.employeeCode = "";
    this.someDBDataSet.inspector.AddinspectorRow(newRow);

    this.inspectorTableAdapter.Fill(this.someDBDataSet.inspector);
    //this.inspectorTableAdapter.ClearBeforeFill = false;
    // TODO: This line of code loads data into the 'someDBDataSet.item' table. You can move, or remove it, as needed.
    this.itemTableAdapter.Fill(this.someDBDataSet.item);
}

解决方案

Eureka! Bind to a view, not table.

Bind inspector_idComboBox to a new SQL Server view of the inspector table.

SELECT NULL as inspector_id, '(none)' as fullName, '' as employeeCode
UNION
SELECT inspector_id, fullName, employeeCode
FROM dbo.inspector

Pros:

1. The (none) item is in the ComboBox
2. The SelectedItem and text persists when selecting the item.
3. The SQL view allows a NULL value for inspector_id
4. No workarounds are needed in the application code. Just fill the DataSet from the view.
5. Allows more flexibility as the relationship is not bound.

... brilliant!

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