如何将DataTable传递回调用方法？

Question

I have been trying to pass a DataTable back to the calling method. Here is the code that calls the Class to create the DataTable .

string SQL = "SELECT .....";
Tables.Create_DataTable(SQL);

Here is the code for the class Tables .

public static class Tables
{
    internal static object Create_DataTable(string SQL)
    {
        DataTable dataTable = new DataTable("Work_Orders");

        using (DataAccessClass.sql_Connection)
        using (SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(SQL, DataAccessClass.sql_Connection))
        {
            DataAccessClass.OpenConnection();

            sqlDataAdapter.Fill(dataTable);
        }

        return Work_Orders;
    }
}

Right after the sqlDataAdapter.Fill(dataTable); there is a Work_Orders DataTable containing the requested data. On the return, I realize that the DataTable is actually an object . This is where I get stuck. How do I change the object to a DataTable ? Then I will add it to the DataSet .

Answer 1

You should return dataTable from your method, but as the basic question the signature should be :

attributes modifiers return-type method-name(parameters )
    {
     statements
    }

Take a look at Here or Here

But change your method like:

internal static DataTable Create_DataTable(string SQL)
{
    DataTable dataTable = new DataTable("Work_Orders");

    using (DataAccessClass.sql_Connection)
    using (SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(SQL, DataAccessClass.sql_Connection))
    {
        DataAccessClass.OpenConnection();

        sqlDataAdapter.Fill(dataTable);
    }

    return dataTable;
}

EDIT:

1- Avoid to return Object from a method

2- Avoid returning DataTable from a method also

because both of them make your code unreadable and unclean, so this is better to return an object which specified for example suppose your DataTable have some fileds about user then this better to be like:

if DataTable have one row:

internal static User Create_DataTable(string SQL)
{
    DataTable dataTable = new DataTable("Work_Orders");

    using (DataAccessClass.sql_Connection)
    using (SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(SQL, DataAccessClass.sql_Connection))
    {
        DataAccessClass.OpenConnection();

        sqlDataAdapter.Fill(dataTable);
    }
     User u = new User()
       { 
          Name = dataTable.Rows[0]("Name"),
          Family = dataTable.Rows[0]("Family"),
          UserName = dataTable.Rows[0]("UserName")
        }
    return u;
}

or if DataTable have infos about several users (Have some rows):

internal static List<User> Create_DataTable(string SQL)
{
    DataTable dataTable = new DataTable("Work_Orders");

    using (DataAccessClass.sql_Connection)
    using (SqlDataAdapter sqlDataAdapter = new SqlDataAdapter(SQL, DataAccessClass.sql_Connection))
    {
        DataAccessClass.OpenConnection();

        sqlDataAdapter.Fill(dataTable);
    }
     List<User> uList = new List<User>();
     foreach (DataRow row in Datatable.Rows) 
     { 
         uList.Add(new User()
              { 
                   Name = row["Name"],
                   Family = row["Family"],
                   UserName = row["UserName"]
               });
      }
    return uList;
}

The above code just are samples.