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，列"Foo"的最小值为0，最大值为100，我需要约束"Foo between 0 And 100"。

如何在 C# 中检查列是否具有此约束？

在访问中，我在 "Validation rules" 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

为了检查对您的 table 施加的约束，您希望使用 OleDbSchemaGuid.Check_Constraints Field。如何使用它实际上与您所说的 OleDbSchemaGuid.Tables 的使用方式略有不同。

为了帮助您解决这个问题，我为您编写了一个小的控制台应用程序，您可以简单地 copy/paste 在 Visual Studio 中的新 控制台应用程序项目 上（或任何首选软件）和运行它以查看它是如何工作的。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，您可以看到约束应用于 Discount table.

的 Discount 字段

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

更新

另外，一般来说，我会建议您熟悉一下 How To Retrieve Column Schema by Using the DataReader GetSchemaTable Method and Visual C# .NET

下面的示例是上面 link 中代码的逐行副本，只是我在该代码中添加了 List of string 并捕获了 table 的字段名称（在 C# 中称为 ColumnName DataColumn），并且我已经用 // ++ Added ++.

标记了我添加的行

OleDbConnection cn = new OleDbConnection(); OleDbCommand cmd = new OleDbCommand(); 数据表架构表； 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.

将非常容易

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