C＃中的数据访问层

Question

I want to create a data access layer in c# for first time. So I read and used tutorials ... now I have a simple code, but this code doesn't work...

for ex: for my delete query...

this is delete web method:

[WebMethod]
public void DeleteMethod(string DBName, string tableName, string attributes, string values)
{
    DBName = DAL.dataAccess.DBname;
    tName = DAL.dataAccess.tName;
    DAL.dataAccess.Delete(attributes, values); 
}

this method pass elements to dataAccess Class and the class create query and connect to my data base. the dataAccess class code for delete query:

public static string DBname { get;set; }

public static string tableName { get;set; }

public static void Delete(string field, string condition)
{
    connect = new SqlConnection(string.Format(_conString, DBname));
    adp.SelectCommand = new SqlCommand();
    adp.SelectCommand.Connection = connect;

    adp.SelectCommand.CommandText = "delete  from " + tName + " where " + field + " = " + condition ;
    DataSet ds = new DataSet();
    connect.Open();
    adp.Fill(ds);
    connect.Close();
}

at first I used cmd.ExecuteNonQuery(); instead of adp.Fill(ds); , but this doesn't work and get error. so I changed my code to this...

Now I get this error at adp.Fill(ds); : "Incorrect syntax near the keyword 'where'."

What is my code problems??

Answer 1

You should use an approach more like below - where you are correctly USING the connections and commands:

using (var connection = new SqlConnection((string.Format(_conString, DBname))
{
    using (var command = connection.CreateCommand())
    {
        connection.Open();
        command.CommandText = "delete  from " + tName + " where " + field +  " = " + condition ; 
        command.ExecuteNonQuery();
    }
}

see here for more details on why you need to use using : [ https://www.dotnetperls.com/sqlconnection]

Answer 2

Try this code in your delete method:-

You can hard code the connection string instead of reading from a config file. Also, for me the table is Employee, for you it could be your table name.

static void Main(string[] args)
    {
        tableName = "Employee";
        string condition = "'User4'";
        Delete("Name", condition);
    }

public static void Delete(string field, string condition)
    {
        string _conString = ConfigurationManager.AppSettings["ConnectionString"];

        using (SqlConnection connect = new SqlConnection(_conString))
        {
            SqlDataAdapter adp = new SqlDataAdapter();

            adp.SelectCommand = new SqlCommand();
            adp.SelectCommand.Connection = connect;

            adp.SelectCommand.CommandText = "delete  from " + tableName + " where " + field + " = " + condition;
            DataSet ds = new DataSet();
            connect.Open();
            adp.Fill(ds);
            connect.Close();
        }
    }