查询int字段查找行，查询char字段不，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';"; 

第一和第二检索该行并在每一种情况下该字段是一个整数，最后一个没有，这是一个字符字段和行确实存在：

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 

有关于通过C＃和OleDB查询字符字段有什么奇怪吗？我尝试过使用'like'而不是'='，并且使用单引号和双引号来分隔值，所有都无济于事。

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

有什么不对您的查询。这是失败的，因为您每次通过在ExecuteQuery中调用OpenDatabase执行查询时都尝试打开与数据库的连接。 OpenDatabase第二次失败，因为数据库已经打开并且查询未执行。

您正在捕获错误，但无所作为。给出的消息是...

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

这可以很容易地通过逐步通过您的代码找到。你没有在调试中运行它吗？

你可以把它改成..

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

如果捕获错误，然后用它做的东西以外返回FALSE