C# 表适配器实际上返回什么? [英] What do C# Table Adapters actually return?

问题描述

堆栈溢出！

我正在开发一个在 Windows 窗体应用程序中操作 SQL 表的应用程序.到目前为止，我只使用了预先生成的 Fill 查询，以及自制的更新和删除查询(不返回任何内容).

I'm working on an application that manipulates SQL tables in a windows form application. Up until now, I've only been using the pre-generated Fill queries, and self-made update and delete queries (which return nothing).

我对存储单个列中单个值的值感兴趣('nchar(15)' 名称)，虽然我很容易编写了 SQL 代码将该值返回给应用程序，但我不知道它将返回什么as.

I am interested in storing the value of a single value from a single column (an 'nchar(15)' name), and though I have easily written the SQL code to return that value to the application, I have no idea what it will be returned as.

SELECT [Contact First Name] FROM ContactSkillSet
WHERE [Contact ID] = @CurrentID

结果可以直接存储为字符串吗?我需要投它吗?调用 toString 方法?

Can the result be stored directly as a string? Do I need to cast it? Invoke a toString method?

谢谢！

有趣的是，以下工作:

String firstName = this.contactSkillSetTableAdapter.GrabFirstName(userKey);

Visual Studio 数据向导的乐趣，我想.

The joys of the Visual Studio data wizard, I suppose.

推荐答案

TableAdapter 用于填充 DataTable.您的示例查询的结果仍将是一个 DataTable，但在一行中有一个列.您可以使用以下方法获取值:

A TableAdapter is used to fill a DataTable. The result of your example query will still be a DataTable but with a single column in a single row. You can get the value using:

var adapter = new SomeKindOfTableAdapter();
var dataTable = new DataTable();

adapter.Fill(dataTable);

string contactFirstName = (string)dataTable.Rows[0][0];

还有其他方法可以在不使用 Table Adapter 的情况下获得您的价值:

There are other ways to get your value without using a Table Adapter though:

string query = @"SELECT [Contact First Name] 
                FROM ContactSkillSet 
                WHERE [Contact ID] = @Current";

string result;

using(SqlConnection conn = new SqlConnection(connString))
{
    conn.Open();

    using(SqlCommand command = new SqlCommand(query, conn))
    {
        result = (string)command.ExecuteScalar();
    }
}

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