Question

我必须找到在数据库（MS Access）中没有域约束的每个列，并且每个列都要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，一列＆＃34; Foo＆＃34;最小值为0，最大值为100，我需要约束＆＃34; Foo介于0和100＆＃34;之间。

如何在C＃中检查列是否存在此约束？

在访问中，我在＆＃34;验证规则＆＃34;。

中找到了这个

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

为了检查桌面上应用的约束，您希望使用OleDbSchemaGuid.Check_Constraints Field。如何使用它实际上与你如何使用OleDbSchemaGuid.Tables有点不同。

为了帮助您，我已经为您编写了一个小的控制台应用程序，您只需在Visual Studio（或任何首选软件）中的新控制台应用程序项目上进行复制/粘贴，然后运行它即可查看这是如何运作的。该示例在着名的 Northwind 数据库上实现。

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();

如果查看输出，可以看到Discount表的Discount字段上应用的约束。

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

<强>更新

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

以下示例是上述链接中代码的逐行副本，但我已在此代码中添加了List string并捕获了表的字段名称（称为ColumnName在此上下文中的C＃DataColumn中，我已使用// ++ Added ++标记了我添加的行。

OleDbConnection cn = new OleDbConnection（）; OleDbCommand cmd = new OleDbCommand（）; DataTable schemaTable; 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中，并了解如何使用它。然后将所需的部件移动到按钮OnClick。

非常容易

如何使用oleDb检查域约束？

1 个答案: