DataSet does not return Data

Question

Hi! I want to get data from an Access Database through a DataSet but all the tables appear to be empty.

using(var x = new DataSet1())
 {
       Console.WriteLine("Am intrat");
       var l = x.Angajati_Detalii.FirstOrDefault();
       foreach(var item in x.Angajati_Detalii)
       {  
            Console.WriteLine(item);
       }
       Console.WriteLine("Am iesit");
 }

This is my code, the DataSet was created automatically from DataSource menu in visual studio.
I checked from the debugger when the program is running but all the tables have count 0.
Am I missing something?
Thank you very much!

Answer 1

Here is an example for reading not using a setup done in a form

public static async Task<DataSet> GetDataSet()
{

    DataSet dataSet = new ();

    await using var cn = new OleDbConnection { ConnectionString = ConnectionString };
    await using var cmd = new OleDbCommand() { Connection = cn };

    cmd.CommandText = "SELECT EmployeeID, FirstName, LastName FROM Employees";

    await cn.OpenAsync();

    DataTable table = new ("EmployeeTable");
    table.Load(cmd.ExecuteReader());

    dataSet.Tables.Add(table);

    return dataSet;
}

Caller

private async void ReadDatSetButton_Click(object sender, EventArgs e)
{

    await Task.Run(async () =>
    {
        DataSet dataSet = await EmployeesOperations.GetDataSet();

        DataTable employeeTable = dataSet.Tables["EmployeeTable"];

        foreach (DataRow row in employeeTable.Rows)
        {
            Debug.WriteLine($"{string.Join(",", row.ItemArray)}");
        }

    });
}

And EF Core is even better, requires the following package. Using Microsoft's common model, blog with post.

Main model - by using model name + Id EF uses it for the primary key, otherwise you need to tell EF via a configuration.

public class Blog
{
    public int BlogId { get; set; }
    public string Url { get; set; }
    public List<Post> Posts { get; set; }
    public override string ToString() => BlogId.ToString();

}

Child model, same thing with the primary key

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public int BlogId { get; set; }
    public Blog Blog { get; set; }
    public override string ToString() => Title;

}

The following uses SQL-Server, change UseSqlServer to whatever the access provider uses.

public class BloggingContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }
    public DbSet<Post> Posts { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlServer(
            "Server=(localdb)\\mssqllocaldb;" + 
            "Database=EFSaving.RelatedData;Trusted_Connection=True");
    }
}

Create the database in code

using (var context = new BloggingContext())
{
    context.Database.EnsureDeleted();
    context.Database.EnsureCreated();
}

Add some data

using (var context = new BloggingContext())
{
    var blog = new Blog
    {
        Url = "http://blogs.msdn.com/dotnet",
        Posts = new List<Post>
        {
            new() { Title = "Intro to C#" },
            new() { Title = "Intro to VB.NET" },
            new() { Title = "Intro to F#" }
        }
    };

    context.Blogs.Add(blog);
    Console.WriteLine($"{context.SaveChanges()}");
}

Read data

foreach (var item in context.Blogs.ToList())
{
    Console.WriteLine($"{item.BlogId}");
    foreach (var postItem in item.Posts)
    {
        Console.WriteLine($"\t{postItem.Title}");
    }
}

Answer 2

This line of code creates a new dataset1 with no data in it.

  using(var x = new DataSet1())
  {

You would have load data into your dataset with your code or fill it from a database or xml file