对 int 字段的查询找到行，对 char 字段的查询没有，c# oledb

Question

使用 C# 和 OleDB 连接到 Access 数据库。

我有三个几乎相同的查询字符串：

"select * from stock_head where sh_id = 19;"
"select * from stock_head where sh_lineno = 32059";
"select * from stock_head where sh_ref='#007705';";

第一个和第二个检索行并且每个情况下的字段都是整数，最后一个不是，它是一个字符字段并且该行确实存在：

ExecuteQuery - select * from stock_head where sh_lineno = 32059
ID 7705, #007705, 32059, NS, 'NO SALE', 04/02/2017 14:29:00
1 row(s) found

ExecuteQuery - select * from stock_head where sh_ref='#007705';
0 row(s) found

通过C#和OleDB查询字符字段有什么奇怪的地方吗？我试过使用 'like' 代替 '='，并用单引号和双引号来分隔值，但都无济于事。

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.OleDb;
using System.Linq;

namespace OleDbTest
{
class Program
{
    static void Main( string[] args )
    {
        // Create Profile File object
        ProcessEJFile EJP = new ProcessEJFile(
            "Provider=Microsoft.ACE.OLEDB.12.0;" +
            @"Data Source=E:\Users\sallyw\Documents\Bar.accdb;" +
            "Persist Security Info=False;");

        //// Get last reference from the Stock Header file
        //object retVal = EJP.ExecuteScalar(
        //    @"SELECT max(stock_head.[sh_ref]) FROM stock_head where sh_ref like ""[#]%"";", null);
        //string maxRef = retVal.ToString();
        //Console.WriteLine( "maxRef = {0}", maxRef );

        // Get the actual row
        string query =
             // @"select * from stock_head where sh_ref = '{0}';";
             //"select * from stock_head where sh_id = 19;";
             "select * from stock_head where sh_lineno = 32059";

        List<StockHead> shlist = EJP.GetStockHead(query, null );
        if ( shlist == null )
        {
            Console.WriteLine( "shlist is null" );
        }
        else
        {
            foreach (StockHead sh in shlist )
            {
                Console.WriteLine( sh.ToString() );
            }
            Console.WriteLine( "{0} row(s) found", shlist.Count());
        }

        query =
             // @"select * from stock_head where sh_ref = '{0}';";
             "select * from stock_head where sh_ref='#007705';";

        List<StockHead> shlist1 = EJP.GetStockHead(query, null );
        if ( shlist1 == null )
        {
            Console.WriteLine( "shlist1 is null" );
        }
        else
        {
            foreach ( StockHead sh in shlist1 )
            {
                Console.WriteLine( sh.ToString() );
            }
            Console.WriteLine( "{0} row(s) found", shlist1.Count() );
        }
        Console.ReadLine();
    }
}

class ProcessEJFile
{
    AccessDatabase Accdb = null;

    public ProcessEJFile( string connectionString )
    {
        Accdb = new AccessDatabase( connectionString );
    }

    public List<StockHead> GetStockHead( string sql, params object[] args )
    {
        DataTable t;

        Accdb.ExecuteQuery( out t, sql, args );

        if ( t != null )
        {
            List<StockHead> shlist = new List<StockHead>();

            foreach ( DataRow r in t.Rows )
            {
                StockHead sh = new StockHead( r);
                shlist.Add( sh );
            }
            return shlist;
        }
        else
        {
            return null;
        }
    }

    // Get a single value - MAX, COUNT etc.
    public Object ExecuteScalar( string sql, params object[] args )
    {
        return Accdb.ExecuteScalar( sql, args );
    }
}


class AccessDatabase
{
    public OleDbConnection conn = new OleDbConnection();

    public AccessDatabase( string connection )
    {
        conn.ConnectionString = connection;
    }

    public bool OpenDatabase()
    {
        try
        {
            conn.Open();
        }
        catch ( Exception ex )
        {
            return false;
        }
        return true;
    }

    public void CloseDatabase()
    {
        if ( conn == null )
            return;

        conn.Close();
    }

    public void ExecuteQuery( out DataTable dataTable, string sql, params object[] args )
    {
        dataTable = new DataTable();
        string query;

        // Simplified version not validating or cleaning arguments in any way
        if ( args == null )
        {
            query = sql;
        }
        else
        {
            query = string.Format( sql, args );
        }

        Console.WriteLine( "\nExecuteQuery - {0}", query );

        if ( OpenDatabase() )
        {
            OleDbCommand command = new OleDbCommand( query, conn );
            OleDbDataAdapter adapter = new OleDbDataAdapter( command );
            adapter.Fill( dataTable );
        }
    }

    public object ExecuteScalar( string sql, params object[] args )
    {
        Object returnValue = null;
        string query = sql;

        if ( OpenDatabase() )
        {
            OleDbCommand cmd = new OleDbCommand( query, (OleDbConnection)conn);
            returnValue = cmd.ExecuteScalar();
        }
        return returnValue;
    }
}

class StockHead
{
    public int sh_id;
    public string sh_ref;
    public int sh_lineno = 0;
    public string sh_type;
    public string sh_supplier = "";
    public DateTime sh_datetime;

    public StockHead( DataRow row )
    {
        this.sh_id = (int)row[ "sh_id" ];
        this.sh_ref = (string)row[ "sh_ref" ];
        if ( !string.IsNullOrEmpty( row[ "sh_lineno" ].ToString() ) )
        {
            this.sh_lineno = (int)row[ "sh_lineno" ];
        }
        this.sh_type = (string)row[ "sh_type" ];
        if ( !string.IsNullOrEmpty( row[ "sh_lineno" ].ToString() ) )
        {
            this.sh_supplier = (string)row[ "sh_supplier" ];
        }
        this.sh_datetime = (DateTime)row[ "sh_datetime" ];
    }

    public override string ToString()
    {
        return String.Format( "ID {0}, {1}, {2}, {3}, '{4}', {5}",
                this.sh_id, this.sh_ref, this.sh_lineno, this.sh_type, this.sh_supplier, this.sh_datetime );
    }
}

}`

Answer 1

您的查询没有问题。这是失败的，因为您每次通过在 ExecuteQuery 中调用 OpenDatabase 来执行查询时都尝试打开与数据库的连接。第二次 OpenDatabase 失败，因为数据库已经打开并且没有执行查询。

您正在捕获错误但未对其进行任何处理。给出的信息是...

The connection was not closed. The connection's current state is open.

这可以通过单步执行您的代码轻松找到。你不是运行它在调试吗？

你可以改成..

public bool OpenDatabase()
{
    try
    {
        if (conn.State != ConnectionState.Open)
        {
            conn.Open();
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
        return false;
    }
    return true;
}

如果你捕获了一个错误，那么除了返回 False 之外做一些事情

对 int 字段的查询找到行，对 char 字段的查询没有，c# oledb

Query on int fields finds row, query on char field doesn't, c# oledb

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