Question

导入期间为使用ko.observableArray()属性扩展的实体运行时出错，而不是在构造函数中作为简单数组[]类型进行扩展。

var customerCtor = function () {
    this.extendedProp = ko.observable(true);
    //this.extendedArray = ko.observableArray(); // causes error: Cannot write a value to a ko.computed unless you specify a 'write' option. If you wish to read the current value, don't pass any parameters.
    this.extendedArray = []; // this works just fine
  };

我在Breeze v1.3.6 DocCode旁边创建了一个测试：exportImportTests.js“在本地存储整个缓存并恢复”作为我的起点，这是新的测试：

test("w/extended Customer, stash entire cache locally and restore", 3, function () {
  var em1 = newEm();

  var store = em1.metadataStore;
  // extend Customer with observables 
  var customerCtor = function () {
    this.extendedProp = ko.observable(true);
    this.extendedArray = ko.observableArray(); // causes error: Cannot write a value to a ko.computed unless you specify a 'write' option. If you wish to read the current value, don't pass any parameters.
    //this.extendedArray = []; // but this will work just fine?
  };

  store.registerEntityTypeCtor("Customer", customerCtor);

  var expected = testData.primeTheCache(em1);
  // grab first Customer, push value onto extendedArray prop
  var custEntity = em1.getEntities(expected.customerType)[0];
  custEntity.extendedArray().push('some-value');  // even when defined as [], Breeze re-writes field as ko.observable

  var exportData = em1.exportEntities();

  var stashName = "stash_everything";
  window.localStorage.setItem(stashName, exportData);

  var importData = window.localStorage.getItem(stashName);
  var em2 = new EntityManager(); // virginal - so register ctor on this instance
  var store2 = em2.metadataStore;
  store2.registerEntityTypeCtor("Customer", customerCtor);
  em2.importEntities(importData);

  var entitiesInCache = em2.getEntities();
  var restoreCount = entitiesInCache.length;
  equal(restoreCount, expected.entityCount,
      "should have restored expected number of all entities");

  var restoredCustomer = em2.getEntities(expected.customerType)[0];
  ok(restoredCustomer.extendedProp(), 'extended property present');
  ok(restoredCustomer.extendedArray().length > 0, 'extended Array present and has data');
});

em2.importEntities(importData);会抛出错误：

Error: Cannot write a value to a ko.computed unless you specify a 'write' option. If you wish to read the current value, don't pass any parameters.
at Error (<anonymous>)
at h [as extendedArray] (http://localhost:47595/Scripts/knockout-2.2.1.js:44:167)
at ctor.initializeEntityPrototype.proto.setProperty (http://localhost:47595/Scripts/breeze.debug.js:14634:31)
at updateTargetPropertyFromRaw (http://localhost:47595/Scripts/breeze.debug.js:13062:24)
at aspectName (http://localhost:47595/Scripts/breeze.debug.js:13025:13)
at Array.forEach (native)
at updateTargetFromRaw (http://localhost:47595/Scripts/breeze.debug.js:13023:19)
at em._inKeyFixup (http://localhost:47595/Scripts/breeze.debug.js:12601:17)
at Array.forEach (native)
at importEntityGroup (http://localhost:47595/Scripts/breeze.debug.js:12568:28)

由于Breeze总是重写构造函数字段（在我的情况下为KO），定义为[]有效。但不确定为什么在预定义属性时会发生这种情况？

有人碰到这个，或者我错过了某处的文档说明？

Answer 1

我们会看一下。

是的，Breeze假设构造函数中添加的每个属性都应该根据当前的“模型库”进行重写，在您的情况下，它是KO。因此，毫不奇怪数组成为ko.observableArray。

此外，由于这样的属性被认为是在Breeze的管辖范围内，我们必须将它与Breeze可观察性和序列化机制联系起来，这意味着我们将其重新编写为Breeze风格的可观察数组。这样的数组是计算的。

显然，我们为“未映射”的属性执行此操作的方式存在一些问题。我们来看看。

N.B。：我假设（并且您的代码确认）数组属性extendedArray是Breeze意义上的“未映射属性”。那应该没问题。

您不应该在构造函数中提及映射的集合导航属性。没有正当理由这样做我能想到的。在构造函数中提及映射属性的主要原因是（a）为其提供默认值或（b）使其可用于自定义（未映射）计算属性。集合导航属性没有合理的替代默认值（默认为空），将它包含在计算中是很少/可避免的。

Breeze导入ko.observableArray（）的实体扩展属性抛出错误

1 个答案: