Newtonsoft问题与IdynamicMetaObjectProvider实施了有关避难所化的类

Question

目前，我偶然发现了newtonsofts json库的问题，这对我来说是一个谜。

我有几个类，这些类正在实现IdynamicMetaObjectProvider接口。将几个对象序列到JSON不是问题，我完全从对象的每个实例中获得了我期望的JSON。

但是，挑战使我头疼。从我到目前为止观察到的内容，似乎库正在缓存它无法找到的每个动态属性的值，并在应用程序运行时保留此功能。因此，例如，我正在遵循三个JSON：

{ "PropA": "1" }
{ "PropA": "2", "PropB": "1" }
{ "PropA": "3", "PropB": "2", "PropC": "1" }

可以选择这一点的jsons将为我遵循.net对象：

{ "PropA": "1" }
{ "PropA": "1", "PropB": "1" }
{ "PropA": "1", "PropB": "1", "PropC": "1" }

但是！如果我将目标类型从实现的iDynamicMetaObjectProvider更改为dicitionary或Dynamic，则测试对象将正确设置属性。

我的班级有一个索引属性，在设置器上设置了一个断点，该设置器已经提供了错误的值（因此，我的类实现都没有问题）。

public abstract class DynamicModelObject : IDynamicMetaObjectProvider //, IPropertyIndexer //, IDictionary<String, Object>
    {
        [NotMapped]
        [JsonIgnore]
        internal Dictionary<String, Object> properties = new Dictionary<String, Object>();
        [IgnoreProperty]
        [JsonIgnore]
        public override Object this[String propertyName]
        {
            get
            {
                object val;
                if (properties.TryGetValue(propertyName, out val)) {
                    return val;
                }
                var prop = this.GetType().GetProperty(propertyName);
                if (prop != null && prop.CanRead) {
                    return prop.GetValue(this);
                }
                return null;
            }
            set
            {
                isDearty = true;
                var prop = this.GetType().GetProperty(propertyName);
                if (prop != null && prop.CanWrite) {
                    prop.SetValue(this, value);
                } else {
                    properties[propertyName] = value;
                }
                var val = value as String;
                if (value == null || (val != null && String.IsNullOrEmpty(val))) {
                    properties.Remove(propertyName);
                }   
            }
        }
        public DynamicMetaObject GetMetaObject(System.Linq.Expressions.Expression parameter)
        {
            return new DynamicDictionaryPropertyStore<DynamicModelObject>(parameter, this);
        }
        [IgnoreProperty]
        public IEnumerable<String> DynamicPropertyMemberNames
        {
            get
            {
                foreach (var key in properties.Keys) {
                    yield return key;
                }
            }
        }
        private List<String> staticProperties = null;
        [IgnoreProperty]
        private IEnumerable<String> StaticPropertyMemberNames
        {
            get
            {
                if (staticProperties == null) {
                    staticProperties = new List<String>();
                    foreach (var prop in this.GetType()
                        .GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.GetProperty)) {
                        if (!Attribute.IsDefined(prop, typeof(IgnorePropertyAttribute)) && !Attribute.IsDefined(prop, typeof(ScriptIgnoreAttribute))) {
                            staticProperties.Add(prop.Name);
                            yield return prop.Name;
                        }
                    }
                } else {
                    foreach (var prop in staticProperties) {
                        yield return prop;
                    }
                }
            }
        }
        [IgnoreProperty]
        private IEnumerable<String> AllPropertyMemberNames
        {
            get
            {
                foreach (var prop in DynamicPropertyMemberNames.Concat(StaticPropertyMemberNames)) {
                    yield return prop;
                }
            }
        }
        private class DynamicDictionaryPropertyStore<T> : DynamicMetaObject where T : DynamicModelObject
        {
            private T target;
            internal DynamicDictionaryPropertyStore(System.Linq.Expressions.Expression parameter, T target)
                : base(parameter, BindingRestrictions.Empty, target)
            {
                this.target = target;
            }
            public override IEnumerable<string> GetDynamicMemberNames()
            {
                return target.DynamicPropertyMemberNames;
            }
            public override DynamicMetaObject BindSetMember(SetMemberBinder binder, DynamicMetaObject value)
            {
                BindingRestrictions restrictions = BindingRestrictions.GetTypeRestriction(Expression, LimitType);
                System.Linq.Expressions.Expression self = System.Linq.Expressions.Expression.Convert(Expression, LimitType);
                if (binder == null) return null;
                var body = System.Linq.Expressions.Expression.Property(self, "Item", System.Linq.Expressions.Expression.Constant(binder.Name));
                var convert = System.Linq.Expressions.Expression.Convert(System.Linq.Expressions.Expression.Constant(value.Value), typeof(object));
                var lambda = System.Linq.Expressions.Expression.Assign(body, convert);
                return new DynamicMetaObject(lambda, restrictions);
            }
            public override DynamicMetaObject BindGetMember(GetMemberBinder binder)
            {
                BindingRestrictions restrictions = BindingRestrictions.GetTypeRestriction(Expression, LimitType);
                System.Linq.Expressions.Expression self = System.Linq.Expressions.Expression.Convert(Expression, LimitType);
                if (binder == null) return null;
                var body = System.Linq.Expressions.Expression.Property(self, "Item", System.Linq.Expressions.Expression.Constant(binder.Name));
                return new DynamicMetaObject(body, restrictions);
            }
        }
    }

发生了什么？

Answer 1

您对DynamicModelObject的实现不正确。在DynamicDictionaryPropertyStore子类中，您进行以下操作：

public override DynamicMetaObject BindSetMember(SetMemberBinder binder, DynamicMetaObject value) {
    BindingRestrictions restrictions = BindingRestrictions.GetTypeRestriction(Expression, LimitType);
    System.Linq.Expressions.Expression self = System.Linq.Expressions.Expression.Convert(Expression, LimitType);
    if (binder == null) return null;
    var body = System.Linq.Expressions.Expression.Property(self, "Item", System.Linq.Expressions.Expression.Constant(binder.Name));
    var convert = System.Linq.Expressions.Expression.Convert(System.Linq.Expressions.Expression.Constant(value.Value), typeof(object));
    var lambda = System.Linq.Expressions.Expression.Assign(body, convert);
    return new DynamicMetaObject(lambda, restrictions);
}

如果您要查看所产生的表达式，则会看到（例如PropA）：

Convert($arg0).Item["PropA"] = Convert("1")

因此，作为一个设置器，您返回调用索引器并分配常数值（1），而不管是什么值通过了什么值。此表达式将在稍后用于所有设置，用于PropA（缓存）。因此，您的问题：所有的设定器都会忽略传递的值，并且将始终为您首次致电它们的值分配值。要修复，请更换此行：

var convert = System.Linq.Expressions.Expression.Convert(System.Linq.Expressions.Expression.Constant(value.Value), typeof(object));

与此：

var convert = System.Linq.Expressions.Expression.Convert(value.Expression, typeof(object));

由此产生的设置器表达式将是：

Convert($arg0).Item["PropA"] = Convert($arg1)

请注意，没有cast柱，只有争论。之后，您的问题将解决。