using System;

using System.Linq;

using System.Data;

using System.Reflection;

using Dapper;

using Microsoft.Data.Sqlite;

using System.ComponentModel;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        using (var connection = new SqliteConnection("Data Source=:memory:"))

        {

            connection.Query<TestModel>("SELECT 'ONE' TestEnumString UNION ALL SELECT 'TWO' UNION ALL SELECT NULL UNION ALL SELECT 'Other' UNION ALL SELECT 'NotExisting'").Dump();

            EnumExtensions.EnumDescriptionCache<TestEnum>.FailOnNotExisting = true;

            //this will throw vvvvvvvvv because of NotExisting

            connection.Query<TestModel>("SELECT 'ONE' TestEnumString UNION ALL SELECT 'TWO' UNION ALL SELECT NULL UNION ALL SELECT 'Other' UNION ALL SELECT 'NotExisting'").Dump();

        }

    }

}

​

public class TestModel

{

    internal DapperableEnum<TestEnum> TestEnumString { get; set;}

    public TestEnum? TestEnum => TestEnumString.Value;

}

​

public enum TestEnum

{

    [Description("ONE")]

    One = 1,

    [Description("TWO")]

    Two = 2,

    Other = 3

}

​

public readonly struct DapperableEnum<TEnum> where TEnum : struct, Enum

{

    public TEnum? Value { get; }

​

    static DapperableEnum()

    {

        SqlMapper.AddTypeHandler(new DapperableEnumHandler<TEnum>());

    }

​

    public DapperableEnum(TEnum value)

    {

        Value = value;

    }

​

    public DapperableEnum(string description)

    {

        Value = description.GetEnumValueFromDescription<TEnum>();

    }

​

    public static implicit operator DapperableEnum<TEnum>(TEnum v) => new DapperableEnum<TEnum>(v);

    public static implicit operator TEnum?(DapperableEnum<TEnum> v) => v.Value;

    public static implicit operator DapperableEnum<TEnum>(string s) => new DapperableEnum<TEnum>(s);

}

​

public class DapperableEnumHandler<TEnum> : SqlMapper.TypeHandler<DapperableEnum<TEnum>> where TEnum : struct, Enum

{

    public override DapperableEnum<TEnum> Parse(object value) => value is DBNull ? null : new DapperableEnum<TEnum>((string)value);

​

    public override void SetValue(IDbDataParameter parameter, DapperableEnum<TEnum> value)

    {

        parameter.DbType = DbType.String;

        parameter.Value = value.Value.GetDescriptionFromEnumValue();

    }

}

​

public static class EnumExtensions

{

    public static TEnum? GetEnumValueFromDescription<TEnum>(this string description) where TEnum : struct, Enum

        => EnumDescriptionCache<TEnum>.Values.TryGetValue(description, out var value) ? value : !EnumDescriptionCache<TEnum>.FailOnNotExisting ? null : throw new ArgumentException("Not found.", nameof(description));

​

    public static string GetDescriptionFromEnumValue<TEnum>(this TEnum? value) where TEnum : struct, Enum

        => value.HasValue ? EnumDescriptionCache<TEnum>.Descriptions[value.Value] : null;

​

    public static class EnumDescriptionCache<TEnum> where TEnum : struct, Enum

    {

        static EnumDescriptionCache()

        {

            var fields = typeof(TEnum).GetFields().Where(field => field.IsLiteral);

            Descriptions = fields

                .Select(field =>

                    ((TEnum)field.GetValue(null), field.GetCustomAttribute<DescriptionAttribute>() is DescriptionAttribute attribute ? attribute.Description : field.Name))

                .ToDictionary(keyValue => keyValue.Item1, keyValue => keyValue.Item2);

            Values = Descriptions.ToDictionary(keyValue => keyValue.Value, keyValue => keyValue.Key);

        }

​

        public static readonly Dictionary<TEnum, string> Descriptions;

        public static readonly Dictionary<string, TEnum> Values;

        public static bool FailOnNotExisting { get; set; }

    }

}