How to connect to SQL server database from a Windows 10 UWP app

With the Windows 10 Fall Creators Update (build 16299) UWP apps can now access SQL Server directly via the standard NET classes (System.Data.SqlClient) – thanks to the newly added support for .NET Standard 2.0 in UWP.

Here is a Northwind UWP demo app:
https://github.com/StefanWickDev/IgniteDemos

We have presented this demo at Microsoft Ignite in September 2017, here is the recording of our session (skip to 23:00 for the SQL demo):
https://myignite.microsoft.com/sessions/53541

Here is the code to retrieve the products from the Northwind database (see DataHelper.cs in the demo). Note that it is exactly the same code that you would write for a Winforms or WPF app – thanks to the .NET Standard 2.0:

public static ProductList GetProducts(string connectionString)
{
    const string GetProductsQuery = "select ProductID, ProductName, QuantityPerUnit," +
        " UnitPrice, UnitsInStock, Products.CategoryID " +
        " from Products inner join Categories on Products.CategoryID = Categories.CategoryID " +
        " where Discontinued = 0";

    var products = new ProductList();
    try
    {
        using (SqlConnection conn = new SqlConnection(connectionString))
        {
            conn.Open();
            if (conn.State == System.Data.ConnectionState.Open)
            {
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = GetProductsQuery;
                    using (SqlDataReader reader = cmd.ExecuteReader())
                    {
                        while (reader.Read())
                        {
                            var product = new Product();
                            product.ProductID = reader.GetInt32(0);
                            product.ProductName = reader.GetString(1);
                            product.QuantityPerUnit = reader.GetString(2);
                            product.UnitPrice = reader.GetDecimal(3);
                            product.UnitsInStock = reader.GetInt16(4);
                            product.CategoryId = reader.GetInt32(5);
                            products.Add(product);
                        }
                    }
                }
            }
        }
        return products;
    }
    catch (Exception eSql)
    {
        Debug.WriteLine("Exception: " + eSql.Message);
    }
    return null;
}

If you need to support earlier versions than the Fall Creators Update, there is also a way for you to call SqlClient APIs from your UWP app package, via the Desktop Bridge. I have a sample for this published here:
https://github.com/Microsoft/DesktopBridgeToUWP-Samples/tree/master/Samples/SQLServer