API Proposal - example code included

[dimzon]

public static class ProposalExtensions
    {
        public static void JustShowMeTheCode(IDbConnection cn)
        {
            var result = cn.Query(
                // allows to use anonymous type as result
                template: new { EmployeeName = "" }, 
                param: new { EmployeeAge = 26 },
                // allows to use 'nameof' for column names and parameter names 
                sql: (t, p) => $"select e.name as {nameof(t.EmployeeName)} from tbl_emp e where e.age>@{nameof(p.EmployeeAge)}");
            foreach (var item in result)
            {
                Console.WriteLine(item.EmployeeName);
            }
        }

        public static IEnumerable<T> Query<T,TParams>(this IDbConnection cnn, T template, Func<T,TParams,string> sql, TParams param,  IDbTransaction? transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null)
        {
            return cnn.Query<T>(sql(default(T),default(TParams)),param,transaction,buffered,commandTimeout,commandType);
        }

        public static IEnumerable<T> Query<T>(this IDbConnection cnn, T template, Func<T,string> sql, IDbTransaction? transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null)
        {
            return cnn.Query<T>(sql(default(T)), param:null, transaction, buffered, commandTimeout, commandType);
        }
    }

[mgravell]

There seems to be two things here:

1. The ability to use a template to hack around not being able to specify the type for anonymous return types
2. The ability to compose the SQL using nameof etc

The first of these is much better approaches using named-tuples, which should already work; consider instead Query<(int Id, string Name)>(...)

The second is arguably much harder to read, but fundamentally composing strings already works; the only new bit here is the template. Honestly, I wonder if this, if wanted, is better approached using the proposed custom string interpolation handler - maybe look here (draft only): https://github.com/DapperLib/DapperAOT/blob/sqlbuilder/test/Dapper.AOT.Test/SqlBuilderTests.cs

I doubt we'd add the PR proposed here into the core, but you can always use it in your own local extension method