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我正在使用 C# (Visual Studio 2015) 并与 MS Access 数据库进行通信。我下面的代码工作正常，除了_statusLadder变量从备忘录数据类型字段返回一个空值（我在 MS Access 中运行相同的查询并提取正确的备忘录值）。

我也试过：

string _statusLadder = "";

有人可以帮我弄清楚如何从 MS Access 中检索备忘录数据类型字段吗？

见代码：

private string retrieveJobByID(int xID)
    {
        connection.Open();
        OleDbCommand command = new OleDbCommand();
        command.Connection = connection;

        command.CommandText = "SELECT TOP 1 [ID], [JOB_NUM], [CUSTOMER], [MODELNO], [CREATE_DATE], [MODEL_FAMILY], [VER], [COM_PROTOCOL], [STATUS_LADDER] FROM tbl_job_tables WHERE([ID] = ?)";
        command.Parameters.Add("@ID", OleDbType.Integer).Value = xID;

        OleDbDataReader reader = command.ExecuteReader();

        string _id = "", _jobnum = "", _customer = "", _modelFamily = "", _modelNum = "", _createDate = "", _ver = "", _comProtocol = "";
        var _statusLadder = "";

        while (reader.Read())
        {
            _id = reader["ID"].ToString();
            _jobnum = reader["JOB_NUM"].ToString();
            _customer = reader["CUSTOMER"].ToString();
            _modelFamily = reader["MODEL_FAMILY"].ToString();
            _modelNum = reader["MODELNO"].ToString();
            _createDate = reader["CREATE_DATE"].ToString();
            _ver = reader["VER"].ToString();
            _comProtocol = reader["COM_PROTOCOL"].ToString();
            _statusLadder = reader["STATUS_LADDER"].ToString();  //<-- This returns empty when it should be ~300 characters.
            Console.WriteLine("Status is: " + _statusLadder);
        }

        if (!reader.IsClosed)
        {
            reader.Close();
        }

        if (connection.State == ConnectionState.Open) { 
            connection.Close();
        }

        string result = _id + "|" + _jobnum + "|" + _customer + "|" + _modelFamily + "|" + _modelNum + "|" + _createDate + "|" + _ver + "|" + _comProtocol + "|" + _statusLadder;


        return result;
    }

编辑- 这是我的 MS Access 2010 设置 (ACCDB) 的一些图片：

(1) - 第一个显示 SQL 查询。我输入了 ID=116 作为参数

(2) - 第二张图片显示了查询的结果。您可以看到“STATUS_LADDER”返回了正确的值。

(3) - 这是字段“STATUS_LADDER”的表设置（在设计模式下）

在此处输入图像描述

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1 回答 1

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我从 Access 数据库中读取备忘录/长文本字段没有问题。试试这个代码（我简化了一些）。

using System.Data.OleDb;   //other standard namespaces needed also.   


public class AccessDataHelper
{
    string myConn;  //value set in this class constructor

     //Constructor
    public AccessDataHelper()
    {
        myConn = System.Configuration.ConfigurationManager.ConnectionStrings["LocalDB"].ToString();
        //If myConn is null, then a real problem.
    }

    public List<KAddress> GetUnvalidatedAddresses()
    {
        List<KAddress> kAddresses = new List<KAddress>();
        string sqlCommandText = String.Empty;

        using (OleDbConnection myOleDbConnection = new OleDbConnection())
        {

            if (myConn != null)
            {
                myOleDbConnection.ConnectionString = myConn;

                sqlCommandText = "SELECT tblAddresses.AddressId, " +
                    "tblAddresses.USPSValidated, tblAddresses.Notes, " +
                    "tblAddresses.Address, tblAddresses.City, tblAddresses.State, tblAddresses.ZIP " +
                    "FROM tblAddresses  " +
                    "WHERE ( ((IsNull(tblAddresses.USPSValidated)) Or ((tblAddresses.USPSValidated) <> 1)) ) ";
                    //Field USPSValidated is an integer 1=USPS valid address

                OleDbCommand oleDbCommand = new OleDbCommand(sqlCommandText, myOleDbConnection);
                oleDbCommand.Connection.Open();
                OleDbDataReader reader = oleDbCommand.ExecuteReader();

                while (reader.Read())
                {
                    KAddress kAddress = new KAddress();

                    kAddress.AddressID = Convert.ToInt32(reader["AddressID"]);
                    kAddress.Notes = reader["Notes"].ToString();    // Notes is a memo,long text field in Access

                    kAddress.Address = reader["Address"].ToString();
                    kAddress.City = reader["City"].ToString();
                    kAddress.State = reader["State"].ToString();
                    kAddress.Zip = reader["Zip"].ToString();

                    kAddresses.Add(kAddress);
                }
            }
        }

        return kAddresses;
    }

} //end of class
于 2019-02-16T19:07:45.147 回答