使用 C# 9 的records作为强类型ID - 路由和查询参数-白红宇的个人博客

发布日期：2021-05-09 05:28:39 浏览次数：16 分类：博客文章

本文共 9681 字，大约阅读时间需要 32 分钟。

�� C# 9 ��record��id��

public record ProductId(int Value);

��id��ASP.NET Core��

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public record ProductId(int Value);public class Product{    public ProductId Id { get; set; }    public string Name { get; set; }    public decimal UnitPrice { get; set; }}

��API��

[ApiController][Route("api/[controller]")]public class ProductController : ControllerBase{    ...    [HttpGet("{id}")]    public ActionResult
   
     GetProduct(ProductId id)    {         return Ok(new Product {                 Id = id,                Name = "Apple",                UnitPrice = 0.8M  			 });    }}

��Get�� /api/product/1��

{    "type": "https://tools.ietf.org/html/rfc7231#section-6.5.13",    "title": "Unsupported Media Type",    "status": 415,    "traceId": "00-3600640f4e053b43b5ccefabe7eebd5a-159f5ca18d189142-00"}

��415��.NET Core ��URL��ProductId��int��ID��

��

��ProductId��

public class ProductIdConverter : TypeConverter{    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType) =>        sourceType == typeof(string);    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType) =>        destinationType == typeof(string);    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)    {        return value switch        {            string s => new ProductId(int.Parse(s)),            null => null,            _ => throw new ArgumentException($"Cannot convert from {value} to ProductId", nameof(value))        };    }    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)    {        if (destinationType == typeof(string))        {            return value switch            {                ProductId id => id.Value.ToString(),                null => null,                _ => throw new ArgumentException($"Cannot convert {value} to string", nameof(value))            };        }        throw new ArgumentException($"Cannot convert {value ?? "(null)"} to {destinationType}", nameof(destinationType));    }}

��string,��int��

��ProductId��TypeConverter��

[TypeConverter(typeof(ProductIdConverter))]public record ProductId(int Value);

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{    "id": {        "value": 1    },    "name": "Apple",    "unitPrice": 0.8}

��id ��json��json��ProductId��

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��Helper

��ID��

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public static class StronglyTypedIdHelper{    private static readonly ConcurrentDictionary
   
     StronglyTypedIdFactories = new();    public static Func
    
      GetFactory
     
      (Type stronglyTypedIdType)        where TValue : notnull    {        return (Func
      
       )StronglyTypedIdFactories.GetOrAdd(            stronglyTypedIdType,            CreateFactory
       
        );    }    private static Func
        
          CreateFactory
         
          (Type stronglyTypedIdType) where TValue : notnull { if (!IsStronglyTypedId(stronglyTypedIdType)) throw new ArgumentException($"Type '{stronglyTypedIdType}' is not a strongly-typed id type", nameof(stronglyTypedIdType)); var ctor = stronglyTypedIdType.GetConstructor(new[] { typeof(TValue) }); if (ctor is null) throw new ArgumentException($"Type '{stronglyTypedIdType}' doesn't have a constructor with one parameter of type '{typeof(TValue)}'", nameof(stronglyTypedIdType)); var param = Expression.Parameter(typeof(TValue), "value"); var body = Expression.New(ctor, param); var lambda = Expression.Lambda
          
           
            >(body, param); return lambda.Compile(); } public static bool IsStronglyTypedId(Type type) => IsStronglyTypedId(type, out _); public static bool IsStronglyTypedId(Type type, [NotNullWhen(true)] out Type idType) { if (type is null) throw new ArgumentNullException(nameof(type)); if (type.BaseType is Type baseType && baseType.IsGenericType && baseType.GetGenericTypeDefinition() == typeof(StronglyTypedId<>)) { idType = baseType.GetGenericArguments()[0]; return true; } idType = null; return false; }}

�� Helper ��

public class StronglyTypedIdConverter
   
     : TypeConverter    where TValue : notnull{    private static readonly TypeConverter IdValueConverter = GetIdValueConverter();    private static TypeConverter GetIdValueConverter()    {        var converter = TypeDescriptor.GetConverter(typeof(TValue));        if (!converter.CanConvertFrom(typeof(string)))            throw new InvalidOperationException(                $"Type '{typeof(TValue)}' doesn't have a converter that can convert from string");        return converter;    }    private readonly Type _type;    public StronglyTypedIdConverter(Type type)    {        _type = type;    }    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)    {        return sourceType == typeof(string)            || sourceType == typeof(TValue)            || base.CanConvertFrom(context, sourceType);    }    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)    {        return destinationType == typeof(string)            || destinationType == typeof(TValue)            || base.CanConvertTo(context, destinationType);    }    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)    {        if (value is string s)        {            value = IdValueConverter.ConvertFrom(s);        }        if (value is TValue idValue)        {            var factory = StronglyTypedIdHelper.GetFactory
    
     (_type);            return factory(idValue);        }        return base.ConvertFrom(context, culture, value);    }    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)    {        if (value is null)            throw new ArgumentNullException(nameof(value));        var stronglyTypedId = (StronglyTypedId
     
      )value;        TValue idValue = stronglyTypedId.Value;        if (destinationType == typeof(string))            return idValue.ToString()!;        if (destinationType == typeof(TValue))            return idValue;        return base.ConvertTo(context, culture, value, destinationType);    }}

�� Converter

public class StronglyTypedIdConverter : TypeConverter{    private static readonly ConcurrentDictionary
   
     ActualConverters = new();    private readonly TypeConverter _innerConverter;    public StronglyTypedIdConverter(Type stronglyTypedIdType)    {        _innerConverter = ActualConverters.GetOrAdd(stronglyTypedIdType, CreateActualConverter);    }    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType) =>        _innerConverter.CanConvertFrom(context, sourceType);    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType) =>        _innerConverter.CanConvertTo(context, destinationType);    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value) =>        _innerConverter.ConvertFrom(context, culture, value);    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType) =>        _innerConverter.ConvertTo(context, culture, value, destinationType);    private static TypeConverter CreateActualConverter(Type stronglyTypedIdType)    {        if (!StronglyTypedIdHelper.IsStronglyTypedId(stronglyTypedIdType, out var idType))            throw new InvalidOperationException($"The type '{stronglyTypedIdType}' is not a strongly typed id");        var actualConverterType = typeof(StronglyTypedIdConverter<>).MakeGenericType(idType);        return (TypeConverter)Activator.CreateInstance(actualConverterType, stronglyTypedIdType)!;    }}

�� ProductIdConvert�� .NET Core ��JSON��

[TypeConverter(typeof(StronglyTypedIdConverter))]public abstract record StronglyTypedId
   
    (TValue Value)    where TValue : notnull{    public override string ToString() => Value.ToString();}

��: thomas levesque
��

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�� QQ�� 897216102

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