使用一组复杂数据类型调用UpdateModel会重置所有非绑定值吗？

Question

我不确定这是否是DefaultModelBinder类中的错误或者是什么.但UpdateModel通常不会更改模型的任何值,除了它找到匹配的值.看看以下内容:

[AcceptVerbs(HttpVerbs.Post)]
public ViewResult Edit(List<int> Ids)
{
    // Load list of persons from the database
    List<Person> people = GetFromDatabase(Ids);
    // shouldn't this update only the Name & Age properties of each Person object
    // in the collection and leave the rest of the properties (e.g. Id, Address)
    // with their original value (whatever they were when retrieved from the db)
    UpdateModel(people, "myPersonPrefix", new string[] { "Name", "Age" });
    // ...
}

会发生什么是UpdateModel创建新的 Person对象,从ValueProvider分配它们的Name和Age属性并将它们放在参数List <>中,这使得其余的属性设置为它们的默认初始值(例如Id = 0),那么什么是去吧？

Answer 1

更新: 我介绍了mvc源代码(特别是DefaultModelBinder类),这是我发现的:

该类确定我们正在尝试绑定一个集合,因此它调用方法:UpdateCollection(...)它创建一个ModelBindingContext具有null Model属性的内部.然后,将该上下文发送到BindComplexModel(...)检查Model属性的方法,如果是这种情况,则null创建模型类型的新实例.

这就是导致值重置的原因.

因此,只填充通过表单/查询字符串/路由数据的值,其余值保持其初始化状态.

我能够做很少的修改UpdateCollection(...)来解决这个问题.

这是我的更改方法:

internal object UpdateCollection(ControllerContext controllerContext, ModelBindingContext bindingContext, Type elementType) {
IModelBinder elementBinder = Binders.GetBinder(elementType);

// build up a list of items from the request
List<object> modelList = new List<object>();
for (int currentIndex = 0; ; currentIndex++) {
    string subIndexKey = CreateSubIndexName(bindingContext.ModelName, currentIndex);
    if (!DictionaryHelpers.DoesAnyKeyHavePrefix(bindingContext.ValueProvider, subIndexKey)) {
        // we ran out of elements to pull
        break;
    }
    // **********************************************************
    // The DefaultModelBinder shouldn't always create a new
    // instance of elementType in the collection we are updating here.
    // If an instance already exists, then we should update it, not create a new one.
    // **********************************************************
    IList containerModel = bindingContext.Model as IList;
    object elementModel = null;
    if (containerModel != null && currentIndex < containerModel.Count)
    {
        elementModel = containerModel[currentIndex];
    }
     //*****************************************************
    ModelBindingContext innerContext = new ModelBindingContext() {
        Model = elementModel, // assign the Model property
        ModelName = subIndexKey,
        ModelState = bindingContext.ModelState,
        ModelType = elementType,
        PropertyFilter = bindingContext.PropertyFilter,
        ValueProvider = bindingContext.ValueProvider
    };
    object thisElement = elementBinder.BindModel(controllerContext, innerContext);

    // we need to merge model errors up
    VerifyValueUsability(controllerContext, bindingContext.ModelState, subIndexKey, elementType, thisElement);
    modelList.Add(thisElement);
}

// if there weren't any elements at all in the request, just return
if (modelList.Count == 0) {
    return null;
}

// replace the original collection
object collection = bindingContext.Model;
CollectionHelpers.ReplaceCollection(elementType, collection, modelList);
return collection;

}