MongoEngine distinct（）过滤和EmbeddedDocument

Question

最近，也许在软件升级之后，我遇到了一个问题：distinct（）过滤现在返回一个字典集合而不是EmbeddedDocument集合。意味着对象的直接遍历按预期工作。

这是一段代码，可能不会被删除而是相当简单。这是一个简单的产品目录，其功能包括按功能过滤等功能：

from mongoengine import *


class FeatureInfo(Document):
    title = StringField()


class ProductFeature(EmbeddedDocument):
    featureInfo = ReferenceField(FeatureInfo)
    value = StringField()

    def eq(a, b):
        return a.featureInfo.title == b.featureInfo.title and a.value == b.value


class Product(Document):
    title = StringField()
    features = ListField(EmbeddedDocumentField(ProductFeature))


def populate():
    producer_feature_info = FeatureInfo("Producer")
    producer_feature_info.save()

    screen_size_feature_info = FeatureInfo("Screen size")
    screen_size_feature_info.save()

    iphone_producer_feature = ProductFeature(featureInfo=producer_feature_info, value="Apple")
    iphone_screen_size_feature = ProductFeature(featureInfo=screen_size_feature_info, value="4 inch")

    iphone = Product(title="iPhone 5S")
    iphone.features.append(iphone_producer_feature)
    iphone.features.append(iphone_screen_size_feature)
    iphone.save()

    galaxy_producer_feature = ProductFeature(featureInfo=producer_feature_info, value="Samsung")
    galaxy_screen_size_feature = ProductFeature(featureInfo=screen_size_feature_info, value="5 inch")

    galaxy = Product(title="Galaxy S4")
    galaxy.features.append(galaxy_producer_feature)
    galaxy.features.append(galaxy_screen_size_feature)
    galaxy.save()

    galaxy_producer_feature = ProductFeature(featureInfo=producer_feature_info, value="Samsung")
    galaxy_screen_size_feature = ProductFeature(featureInfo=screen_size_feature_info, value="4 inch")

    galaxy = Product(title="Galaxy S2")
    galaxy.features.append(galaxy_producer_feature)
    galaxy.features.append(galaxy_screen_size_feature)
    galaxy.save()


if __name__ == "__main__":
    connect('test')
    populate()

    products = Product.objects()

    print "\n".join(map(lambda p: p.title + " [" + ", ".join(map(lambda f: f.featureInfo.title + " = " + f.value, p.features)) + "]", products))

    print "\nProduct features"

    features = []

    for product in products:
        print product.title
        for feature in product.features:
            if feature not in features:
                features.append(feature)
            print feature.__class__.__name__

    print "\nUnique features"

    for feature in features:
        print feature.featureInfo.title + " = " + feature.value + " (" + feature.__class__.__name__ + ")"

    print "\nDistinct features"

    features = products.distinct("features")

    for feature in features:
        print feature.__class__.__name__

这是输出：

python test.py 
iPhone 5S [Producer = Apple, Screen size = 4 inch]
Galaxy S4 [Producer = Samsung, Screen size = 5 inch]
Galaxy S2 [Producer = Samsung, Screen size = 4 inch]

Product features
iPhone 5S
ProductFeature
ProductFeature
Galaxy S4
ProductFeature
ProductFeature
Galaxy S2
ProductFeature
ProductFeature

Unique features
Producer = Apple (ProductFeature)
Screen size = 4 inch (ProductFeature)
Producer = Samsung (ProductFeature)
Screen size = 5 inch (ProductFeature)

Distinct features
BaseDict
BaseDict
BaseDict
BaseDict

我在StackOverflow上发现了这样一个问题，但MongoEngine 0.8.3存在问题，0.8.4存在问题。我跟着它升级但没有效果。