This file add overloads for each Dapper.SQLMapper method, allowing the use of FormattableString for building parametrized queries. Each parameter of string will be converted into a SQL parameter.

SqlMapperExtensions.cs

using System.Data;
using System.Globalization;
using System.Text.RegularExpressions;

/*
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* This file add overloads for each Dapper.SQLMapper method, allowing the use of FormattableString     *
* for building parametrized queries. Each parameter of string will be converted into a SQL parameter. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
*/

namespace Dapper
{
    /// <inheritdoc cref="SqlMapper"/>
    public static class SqlMapperExtensions
    {
        private const string DefaultParameterPrefix = "@__p";

        #region Public Methods

        /// <inheritdoc cref="SqlMapper.Execute"/>
        public static int Execute(this IDbConnection cnn, FormattableString sql, object? param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null, string parameterPrefix = DefaultParameterPrefix, CultureInfo culture = null)
        {
            var (queryString, parameters) = sql.ToDapper(parameterPrefix, param, culture);
            return cnn.Execute(queryString, parameters, transaction, commandTimeout, commandType);
        }

        /// <inheritdoc cref="SqlMapper.ExecuteAsync"/>
        public static Task<int> ExecuteAsync(this IDbConnection cnn, FormattableString sql, object? param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null, string parameterPrefix = DefaultParameterPrefix, CultureInfo culture = null)
        {
            var (queryString, parameters) = sql.ToDapper(parameterPrefix, param, culture);
            return cnn.ExecuteAsync(queryString, parameters, transaction, commandTimeout, commandType);
        }

        /// <inheritdoc cref="SqlMapper.Query{T}"/>
        public static IEnumerable<T> Query<T>(this IDbConnection cnn, FormattableString sql, object? param = null, IDbTransaction transaction = null, bool buffered = true, int? commandTimeout = null, CommandType? commandType = null, string parameterPrefix = DefaultParameterPrefix, CultureInfo culture = null)
        {
            var (queryString, parameters) = sql.ToDapper(parameterPrefix, param, culture);
            return cnn.Query<T>(queryString, parameters, transaction, buffered, commandTimeout, commandType);
        }

        /// <inheritdoc cref="SqlMapper.QueryAsync{T}"/>
        public static Task<IEnumerable<T>> QueryAsync<T>(this IDbConnection cnn, FormattableString sql, object? param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null, string parameterPrefix = DefaultParameterPrefix, CultureInfo culture = null)
        {
            var (queryString, parameters) = sql.ToDapper(parameterPrefix, param, culture);
            return cnn.QueryAsync<T>(queryString, parameters, transaction, commandTimeout, commandType);
        }

        /// <inheritdoc cref="SqlMapper.QueryFirst{T}"/>
        public static T QueryFirst<T>(this IDbConnection cnn, FormattableString sql, object? param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null, string parameterPrefix = DefaultParameterPrefix, CultureInfo culture = null)
        {
            var (queryString, parameters) = sql.ToDapper(parameterPrefix, param, culture);
            return cnn.QueryFirst<T>(queryString, parameters, transaction, commandTimeout, commandType);
        }

        /// <inheritdoc cref="SqlMapper.QueryFirstAsync{T}"/>
        public static Task<T> QueryFirstAsync<T>(this IDbConnection cnn, FormattableString sql, object? param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null, string parameterPrefix = DefaultParameterPrefix, CultureInfo culture = null)
        {
            var (queryString, parameters) = sql.ToDapper(parameterPrefix, param, culture);
            return cnn.QueryFirstAsync<T>(queryString, parameters, transaction, commandTimeout, commandType);
        }

        /// <inheritdoc cref="SqlMapper.QueryFirstOrDefault{T}"/>
        public static T QueryFirstOrDefault<T>(this IDbConnection cnn, FormattableString sql, object? param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null, string parameterPrefix = DefaultParameterPrefix, CultureInfo culture = null)
        {
            var (queryString, parameters) = sql.ToDapper(parameterPrefix, param, culture);
            return cnn.QueryFirstOrDefault<T>(queryString, parameters, transaction, commandTimeout, commandType);
        }

        /// <inheritdoc cref="SqlMapper.QueryFirstOrDefaultAsync{T}"/>
        public static Task<T> QueryFirstOrDefaultAsync<T>(this IDbConnection cnn, FormattableString sql, object? param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null, string parameterPrefix = DefaultParameterPrefix, CultureInfo culture = null)
        {
            var (queryString, parameters) = sql.ToDapper(parameterPrefix, param, culture);
            return cnn.QueryFirstOrDefaultAsync<T>(queryString, parameters, transaction, commandTimeout, commandType);
        }

        /// <summary>
        /// Converts a FormattableString to a Dapper query and DynamicParameters.
        /// </summary>
        /// <param name="sql">The FormattableString to convert.</param>
        /// <param name="parameterPrefix">the prefix used for each parameter</param>
        /// <param name="aditionalParameters">Append aditional parameters using <see cref="DynamicParameters.AddDynamicParams(object)"/></param>
        /// <returns>A tuple containing the query string and DynamicParameters.</returns>
        public static (string query, DynamicParameters parameters) ToDapper(this FormattableString sql, string parameterPrefix = null, object aditionalParameters = null, CultureInfo culture = null)
        {
            culture = culture ?? culture ?? CultureInfo.InvariantCulture;
            parameterPrefix = string.IsNullOrWhiteSpace(parameterPrefix) ? DefaultParameterPrefix : parameterPrefix;
            var dynamicParameters = new DynamicParameters();
            for (int i = 0; i < sql.ArgumentCount; i++)
            {
                var arg = sql.GetArgument(i);
                var format = sql.Format;
                var index = "{" + i + ":";
                var f = format.IndexOf(index);
                if (f >= 0)
                {
                    if (arg is IFormattable farg && farg != null)
                    {
                        var argumentFormat = format.Substring(f + index.Length);
                        argumentFormat = argumentFormat.Substring(0, argumentFormat.IndexOf("}"));
                        arg = farg.ToString(argumentFormat, culture);
                    }
                    else
                    {
                        arg = arg?.ToString();
                    }
                }

                dynamicParameters.Add($"{parameterPrefix}{i}", arg);
            }

            if (aditionalParameters != null)
            {
                dynamicParameters.AddDynamicParams(aditionalParameters);
            }
            var q = new Regex(@"\{(\d+)(:[^}]+)?\}").Replace(sql.Format, match => $"{parameterPrefix}{match.Groups[1].Value}");
            return (query: q, parameters: dynamicParameters);
        }

        #endregion Public Methods
    }
}