c# - 如何使用 oleDb 检查域约束？

Question

我必须找到数据库(MS Access)中没有域约束的每一列，并为每一列计算当前数据的最小值和最大值，然后从我的程序中添加相应的约束。

例如，“Foo”列的最小值为 0，最大值为 100，我需要约束“Foo 在 0 和 100 之间”。

如何在 C# 中检查列是否具有此约束？

在访问中，我在“验证规则”中找到了此内容。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;


namespace Proiect
{
public partial class Form1 : Form
{

    private OleDbConnection con = new OleDbConnection();
    private new OleDbCommand cmd = new OleDbCommand();

    public Form1()
    {

        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        // TODO: This line of code loads data into the 'dataSet1.Carti'     
        this.cartiTableAdapter.Fill(this.dataSet1.Carti);
        cartiTableAdapter.Fill(dataSet1.Carti);
        dataGridView1.AllowUserToAddRows = false;
        dataGridView1.AllowUserToDeleteRows = false;
        dataGridView1.ReadOnly = true;
        con.ConnectionString="Provider=Microsoft.ACE.OLEDB.12.0;"+
       "DataSource=D:\..\BD.accdb";
        cmd.Connection=con; 
        this.cartiTableAdapter.Fill(this.dataSet1.Carti);
        chkC.Checked=false;

    }

    private void chkC_CheckedChanged(object sender, EventArgs e)
    {

    }

     }
    } 

Answer 1

为了检查应用于您的表的约束，您希望使用 OleDbSchemaGuid.Check_Constraints Field 。如何使用它实际上与您使用 OleDbSchemaGuid.Tables 的方式略有不同。

为了帮助您解决此问题，我为您编写了一个小控制台应用程序，您只需将其复制/粘贴到 Visual Studio(或任何首选软件)中的新控制台应用程序项目上，然后运行它即可查看这是如何运作的。该示例是在著名的 Northwind 数据库上实现的。

OleDbConnection cn = new OleDbConnection();
OleDbCommand cmd = new OleDbCommand();

//Open a connection to the SQL Server Northwind database.
// This is the sample DB I have used in my example.
cn.ConnectionString = "Provider=SQLOLEDB;Data Source=SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=SSPI;";
cn.Open();

//Retrieve records from the Employees table into a DataReader.
cmd.Connection = cn;
cmd.CommandText = "SELECT * FROM Employees";

//Retrieve column schema into a constraints.
var schemaTable = cn.GetOleDbSchemaTable(OleDbSchemaGuid.Check_Constraints,null);

//For each field in the table...
foreach (DataRow myField in schemaTable.Rows)
{
    //For each property of the field...
    foreach (DataColumn myProperty in schemaTable.Columns)
    {
        //Display the field name and value.
        Console.WriteLine(myProperty.ColumnName + " = " + myField[myProperty].ToString());
    }
    Console.WriteLine();

    //Pause.
}
Console.WriteLine("Done");
Console.ReadLine();
//Always close the DataReader and connection.
cn.Close();

如果您查看输出，您可以看到应用于 Discount 表的 Discount 字段的约束。

CONSTRAINT_CATALOG = Northwind
CONSTRAINT_SCHEMA = dbo
CONSTRAINT_NAME = CK_Discount
CHECK_CLAUSE = ([Discount]>=(0) AND [Discount]<=(1))
DESCRIPTION =

更新

一般来说，我会建议您熟悉 How To Retrieve Column Schema by Using the DataReader GetSchemaTable Method and Visual C# .NET

下面的示例是上面链接中代码的逐行副本，除了我已向此代码添加了 string 的 List 并捕获了表的字段名称(在本上下文中，在 C# DataColumn 中称为 ColumnName)，并且我已使用 //++ 添加++ 标记了我添加的行。

OleDbConnection cn = new OleDbConnection(); OleDbCommand cmd = new OleDbCommand(); 数据表模式表； OleDbDataReader myReader;

//Open a connection to the SQL Server Northwind database.
cn.ConnectionString = "Provider=SQLOLEDB;Data Source=EINSTEINIUM\\SQL2014EXPRESS;Initial Catalog=Northwind;Integrated Security=SSPI;Encrypt=False;TrustServerCertificate=False";
cn.Open();

//Retrieve records from the Employees table into a DataReader.
cmd.Connection = cn;
cmd.CommandText = "SELECT * FROM Employees";
myReader = cmd.ExecuteReader(CommandBehavior.KeyInfo);

//Retrieve column schema into a DataTable.
schemaTable = myReader.GetSchemaTable();

// ++ Added ++
var listOfTableFields = new List<string>();

//For each field in the table...
foreach (DataRow myField in schemaTable.Rows)
{
    //For each property of the field...
    foreach (DataColumn myProperty in schemaTable.Columns)
    {
        //Display the field name and value.
        Console.WriteLine(myProperty.ColumnName + " = " + myField[myProperty].ToString());

        // ++ Added ++
        if (myProperty.ColumnName == "ColumnName")
        {
            listOfTableFields.Add(myField[myProperty].ToString());
        }
    }
    Console.WriteLine();

    //Pause.
}

//Always close the DataReader and connection.
myReader.Close();
cn.Close();

// ++ Added ++
Console.WriteLine("List of fields in Employees table.");
// List of Fields in the Employees table.
foreach (var fieldName in listOfTableFields)
{
    Console.WriteLine(fieldName);
}

Console.ReadLine();

将此代码粘贴到控制台应用程序中并了解如何使用它。然后将您需要的部分移动到按钮 OnClick 上将非常容易。