In a Nutshell

Dapper.QX revolves around the Query<TResult> class. Use this to encapsulate a SQL statement along with its available parameters. Here's a very simple case.

public class EmployeesResult
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime HireDate { get; set; }
}

public class EmployeesQuery : Query<EmployeesResult>
{
    public Employees() : base("SELECT * FROM [dbo].[Employee] {where} ORDER BY [LastName], [FirstName]")

    [Where("[HireDate]>=@minHireDate")]
    public DateTime? MinHireDate { get; set; }

    [Where("[HireDate]<=@maxHireDate")]
    public DateTime? MaxHireDate { get; set; }
}

Here we've defined a result class followed by a Query class that uses the result. The Query class has two optional parameters MinHireDate and MaxHireDate. Use the query like this:

using (var cn = GetConnection())
{
    var results = await new EmployeesQuery() 
    {
        MinHireDate = new DateTime(2019, 1, 1) 
    }.ExecuteAsync(cn);
}

Key points:

• Use a Query<TResult> class to define your queries, passing the SQL to the base constructor.
• Use {where} or {andWhere} within your SQL to indicate where criteria is injected.
• Add properties to your query class that correspond to parameters in the query. Implement optional criteria as nullable properties decorated with the [Where] or [Case] attributes. There's more you can do with properties, but these are good starting point.
• Writing result classes (EmployeesResult in the example above) by hand can be very tedious. I offer a free tool to help with this: Postulate.Zinger
• There are several Execute overloads, all async: ExecuteAsync, ExecuteSingleAsync and ExecuteSingleOrDefaultAsync. These all require an open database connection. I use a fictional GetConnection method above just as example. Your connection code will likely look a little different.