SqlMapper.TypeHandler.cs

using System;
using System.Data;

namespace Dapper
{
    public static partial class SqlMapper
    {
        /// <summary>
        /// Base-class for simple type-handlers
        /// </summary>
        /// <typeparam name="T">This <see cref="Type"/> this handler is for.</typeparam>
        public abstract class TypeHandler<T> : ITypeHandler
        {
            /// <summary>
            /// Assign the value of a parameter before a command executes
            /// </summary>
            /// <param name="parameter">The parameter to configure</param>
            /// <param name="value">Parameter value</param>
            public abstract void SetValue(IDbDataParameter parameter, T value);

            /// <summary>
            /// Parse a database value back to a typed value
            /// </summary>
            /// <param name="value">The value from the database</param>
            /// <returns>The typed value</returns>
            public abstract T Parse(object value);

            void ITypeHandler.SetValue(IDbDataParameter parameter, object value)
            {
                if (value is DBNull)
                {
                    parameter.Value = value;
                }
                else
                {
                    SetValue(parameter, (T)value);
                }
            }

            object ITypeHandler.Parse(Type destinationType, object value)
            {
                return Parse(value);
            }
        }

        /// <summary>
        /// Base-class for simple type-handlers that are based around strings
        /// </summary>
        /// <typeparam name="T">This <see cref="Type"/> this handler is for.</typeparam>
        public abstract class StringTypeHandler<T> : TypeHandler<T>
        {
            /// <summary>
            /// Parse a string into the expected type (the string will never be null)
            /// </summary>
            /// <param name="xml">The string to parse.</param>
            protected abstract T Parse(string xml);

            /// <summary>
            /// Format an instance into a string (the instance will never be null)
            /// </summary>
            /// <param name="xml">The string to format.</param>
            protected abstract string Format(T xml);

            /// <summary>
            /// Assign the value of a parameter before a command executes
            /// </summary>
            /// <param name="parameter">The parameter to configure</param>
            /// <param name="value">Parameter value</param>
            public override void SetValue(IDbDataParameter parameter, T value)
            {
                parameter.Value = value == null ? (object)DBNull.Value : Format(value);
            }

            /// <summary>
            /// Parse a database value back to a typed value
            /// </summary>
            /// <param name="value">The value from the database</param>
            /// <returns>The typed value</returns>
            public override T Parse(object value)
            {
                if (value == null || value is DBNull) return default;
                return Parse((string)value);
            }
        }
    }
}