各位帮忙啊！关于提示表没有主键问题

编译提示：System.Data.MissingPrimaryKeyException:  表没有主键。  
代码：  
public  void  SavePhoto(string  data_id,byte[]  p_Blob,string  imgType)  
{  
OracleConnection  cn=new  OracleConnection("User  id=abc;Data  Source=web;password=abc");  //oracle数据库  
cn.Open();  
OracleDataAdapter  photoAdapter;    //da  
DataSet  photoDataSet;                        //dataset  
DataTable  photoTable;                        //table  
DataRow  photoRow;                                //datarow  
 
photoAdapter  =  new  OracleDataAdapter("select  imgtitle,imgdata    from  image  where  imgtitle='"+data_id+"'",cn);                                
photoDataSet=  new  DataSet("image");                  
string  strSQL="select  imgtitle,imgdata    from  image  where  imgtitle='"+data_id+"'";    
OracleCommand  acm=new  OracleCommand(strSQL,cn);  
OracleDataReader  odr=acm.ExecuteReader();  
Response.Write(strSQL);  
 
photoAdapter.UpdateCommand  =  new  OracleCommand("update  image  set  imgdata  =  :vPHOTO  where  imgtitle  =  :vID",cn);  
Response.Write("update  image  set  imgdata  =  :vPHOTO  where  imgtitle  =  :vID");  
 
photoAdapter.UpdateCommand.Parameters.Add(":vPHOTO",OracleType.Blob,  p_Blob.Length,"imgdata");  
photoAdapter.UpdateCommand.Parameters.Add(":vID",OracleType.VarChar,50,"imgtitle");  
photoAdapter.MissingSchemaAction  =  MissingSchemaAction.AddWithKey;  
photoAdapter.FillSchema(photoDataSet,  SchemaType.Source,"image");  
photoAdapter.Fill(photoDataSet,"image");  
photoTable  =  photoDataSet.Tables["image"];  
photoRow  =  photoTable.Rows.Find(data_id);//这句提示的错误  
                                             
photoRow.BeginEdit();  
if  (p_Blob.Length  !=  0)  
{  
photoRow["imgdata"]  =  p_Blob;  
}  
photoRow.EndEdit();                                                  
photoAdapter.Update(photoDataSet,"image");  
 
 
}