Automapper Project 无法使用结构创建地图表达式

Question

在使用 ProjectTo 查询时，是否有办法支持“包装”域模型作为映射中的结构？ 例如，我有一个名为 Edition 的结构，它代表一个许可证版本。在数据库中，此类列存储为Integer。但是，在使用 WebApi 时，此类字段会以 struct Edition 的形式返回。您可能会问，如果它是 WebApi，只需在模型中返回 int 即可。好吧，这就是我们在幕后所做的，但我们还有一个用于 api 的 SDK，在这个 SDK 中，我们将返回的类建模为具有 Edition 而不是 int，因此开发人员很清楚什么数据的意思。 我们创建了 .net TypeConverters 和 Newtonjson 转换器，一切看起来都不错，除了 AutoMapper 在使用 ProjectTo<MyModel> 时抛出异常

Unable to create a map expression from ScriptVersion.License (System.Nullable`1[System.Int32]) to ScriptVersionModel.License (System.Nullable`1[Licensing.Edition])
Mapping types:
ScriptVersion -> ScriptVersionModel
Contracts.ScriptVersion -> Api.V10.ScriptVersionModel
Type Map configuration:
ScriptVersion -> ScriptVersionModel
Contracts.ScriptVersion -> Api.V10.ScriptVersionModel
Property:
License

Edition + EditionTypeConverter

[TypeConverter(typeof(EditionTypeConverter))]
    [Serializable]
    public struct Edition : ISerializable
    {
        /// <summary>
        /// Prefer using <see cref="Edition.Community"/> instead.
        /// This only exists to support using <see cref="Edition"/> on <see cref="System.Attribute"/>.
        /// </summary>
        public const int CommunityNumber = 1024;
        /// <summary>
        /// Prefer using <see cref="Edition.Standard"/> instead.
        /// This only exists to support using <see cref="Edition"/> on <see cref="System.Attribute"/>.
        /// </summary>
        public const int StandardNumber = 1025;
        /// <summary>
        /// Prefer using <see cref="Edition.Enterprise"/> instead.
        /// This only exists to support using <see cref="Edition"/> on <see cref="System.Attribute"/>.
        /// </summary>
        public const int EnterpriseNumber = 1026;
        public static readonly Edition NotLicensed = new Edition(0);
        public static readonly Edition Community = new Edition(CommunityNumber);
        public static readonly Edition Standard = new Edition(StandardNumber);
        public static readonly Edition Enterprise = new Edition(EnterpriseNumber);
        private readonly int edition;

        public Edition(int edition)
        {
            this.edition = edition;
        }

        public Edition(SerializationInfo info, StreamingContext context)
        {
            edition = (int)info.GetValue(nameof(edition), typeof(int));
        }

        public override string ToString()
        {
            if (edition == NotLicensed)
                return "Not Licensed";
            if (edition == Community)
                return nameof(Community);
            if (edition == Standard)
                return nameof(Standard);
            if (edition == Enterprise)
                return nameof(Enterprise);

            return $"Unknown({edition})";
        }

        public override bool Equals(object obj)
        {
            if (obj == null)
                return false;
            if (!(obj is Edition))
                return false;

            var token = (Edition)obj;
            return token.edition == edition;
        }

        public override int GetHashCode() => edition.GetHashCode();

        void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
        {
            info.AddValue(nameof(edition), edition);
        }

        public static bool operator !=(Edition left, Edition right) => !(left == right);
        public static implicit operator int(Edition edition) => edition.edition;
        public static bool operator ==(Edition left, Edition right)
        {
            if (ReferenceEquals(left, null))
                return ReferenceEquals(right, null);

            return left.Equals(right);
        }

        public static Edition? From(int? edition) => edition.HasValue ? new Edition(edition.Value) : (Edition?)null;

        public class EditionTypeConverter : TypeConverter
        {
            public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
            {
                return sourceType.GetActualType() == typeof(int) ||
                    sourceType.GetActualType() == typeof(long) ||
                    base.CanConvertFrom(context, sourceType);
            }

            public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
            {
                if (value == null)
                    return null;

                if (int.TryParse(value.ToString(), out int edition))
                    return new Edition(edition);
                if (long.TryParse(value.ToString(), out long longEdition))
                    return new Edition((int)longEdition);

                return base.ConvertFrom(context, culture, value);
            }
        }
    }

ScriptVersionModel - 从 WebApi 返回

public class ScriptVersionModel
{
   public Edition? License{get;set;}
}

ScriptVersion - 实体框架类映射到数据库

public class ScriptVersion
{
   public int? License{get;set;}
}

触发错误的代码

context.ScriptVersions.Where(predicate).ProjectTo<ScriptVersionModel>();

Answer 1

你可以用这个

public IMapper InitializeMapper()
{
    var configuration = new MapperConfiguration(cfg =>
    {
        cfg.CreateMap<ScriptVersion, ScriptVersionModel>().ForMember(a => a.License, map => map.MapFrom(src => new Edition(src.License ?? 0)));
    });
    return configuration.CreateMapper();
}

然后

var mapper = InitializeMapper();
ScriptVersionModel edition = mapper.Map<ScriptVersionModel>(new ScriptVersion { License = 12 });

或

context.ScriptVersions.Where(predicate).ProjectTo<ScriptVersionModel>();