Question

在ZOBD中（在Python 3.x中）我希望能够将对象存储为BTrees.OOBTree.OOBTree()中的键。我尝试时得到的错误示例（请参阅注释）：

from BTrees.OOBTree import OOBTree as Btree

class Test:
    pass

bt=Btree()
t=Test()
bt[t]=None #TypeError: Object has default comparison

所以，我在某处读到可能需要定义__eq__来删除该错误，但是虽然这似乎解决了以前的问题但似乎会导致更多问题。例如：

[编辑：应该注意的是，我在这里发现了继承OOBTree（和TreeSet）的一些问题。显然，他们没有妥善保存;所以，它与继承Persistent不一样，即使它们继承了Persistent。]

from BTrees.OOBTree import OOBTree as Btree

class Test:
    def __eq__(self, other): #Maybe this isn't the way to define the method
        return self==other

bt=Btree()
t=Test()
bt[t]=None

t in bt #TypeError: unorderable types: Test() < Test()

在BTree或OOBTree中使用对象作为键的正确方法是什么？我确实需要测试密钥是否存在。

对于那些不了解的人来说，ZODB中的BTree非常类似于可扩展的Python字典（它们应该可以使用比常规Python字典更多的键值对）来设计持久性。

Answer 1

我认为this answer可以帮助解决您的问题。

基本上，您必须在对象上重新实现三种方法：

var menus = (from menu in XDocument.Parse(xml).Descendants("Menu") select new { TextField = (string)menu.Attribute("TextField") }).ToList();（平等检查）
__eq__（非等同性检查）
__ne__使对象真正可序列化为字典键

Answer 2

尽管艾略特·贝里奥特的回答让我得到了我需要的答案，但我想我会发布完整的答案，这些答案对我有帮助，所以其他人不必花费额外的时间来解决问题。（我将以第二人称自言自语。）

首先（我没有真正问过它，但它可能是你想要做的事情），不要继承OOBTree或OOTreeSet（这会导致问题）。创建自己的继承Persistent的类，并在其中放置一个OOBTree或OOTreeSet，如果你想要一个像继承的OOBTree那样的东西（同样，如果你想要的话，定义使它看起来像字典或集合所需的方法）。 p>

接下来，您需要创建一个Persistent ID系统（对于放在OOBTree或OOTreeSet中的每个对象，因为如果您没有ZOBD可以使用的唯一整数，则对象会导致OOBTrees和OOTreeSets出现故障你需要定义Eliot提到的方法，以及其他类似的方法（这些方法需要比较整数ID，而不是对象本身）;即定义生成对象的类的这些方法它将是OOBTree的键或包含在OOTreeSet中：__eq__，__ne__，__hash__，__lt__，__le__，__gt__和__ge__。但是，为了获得持久性ID，您将不得不制作ID计数器类或其他东西（因为它不会将普通整数保存为OOBTree中的值，因为某些奇怪的是，除非我做错了），并且那个计数器类也必须有一个ID。

接下来，你需要确保如果你正在制作对象键，那么你最好不要在同一个OOBTree中使字符串成为键，否则你就会变得神秘问题（由于字符串与您的对象没有相同的ID系统）。它会将字符串键与您的对象键进行比较，并导致错误，因为它们并非设计用于比较。

这是Python 3.x代码的一个工作示例，它允许您将对象用作OOBTree中的键，并且它允许您迭代OOBTree中的持久对象（并将它们用作键）。它还向您展示了如何保存和加载对象。

对不起它有点长，但它应该让你知道这是如何工作的：

import transaction, ZODB, ZODB.FileStorage
from persistent import Persistent
from BTrees.OOBTree import OOBTree as OOBTree
from BTrees.OOBTree import OOTreeSet as OOTreeSet

class Btree(Persistent):
    def __init__(self, ID=None, **attr):
        #I like to use entirely uppercase variables to represent ones you aren't supposed to access outside of the class (because it doesn't have the restrictions that adding _ and __ to the beginning do, and because you don't really need all caps for constants in Python)
        Persistent.__init__(self)
        self.DS=OOBTree() #DS stands for data structure
        self.DS.update(attr)
        if ID==None:
            self.ID=-1 #To give each object a unique id. The value, -1, is replaced.
            self.ID_SET=False
        else:
            self.ID=ID #You should remember what you’re putting here, and it should be negative.
            self.ID_SET=True
    def clear(self):
        self.DS.clear()
    def __delitem__(self, key):
        del self.DS[key]
    def __getitem__(self, key):
        return self.DS[key]
    def __len__(self):
        return len(self.DS)
    def __iadd__(self, other):
        self.DS.update(other)
    def __isub__(self, other):
        for x in other:
            try:
                del self.DS[x]
            except KeyError:
                pass
    def __contains__(self, key):
        return self.DS.has_key(key)
    def __setitem__(self, key, value):
        self.DS[key]=value
    def __iter__(self):
        return iter(self.DS)
    def __eq__(self, other):
        return self.id==other.id
    def __ne__(self, other):
        return self.id!=other.id
    def __hash__(self):
        return self.id
    def __lt__(self, other):
        return self.id<other.id
    def __le__(self, other):
        return self.id<=other.id
    def __gt__(self, other):
        return self.id>other.id
    def __ge__(self, other):
        return self.id>=other.id
    @property
    def id(self):
        if self.ID_SET==False:
            print("Warning. self.id_set is False. You are accessing an id that has not been set.")
        return self.ID
    @id.setter
    def id(self, num):
        if self.ID_SET==True:
            raise ValueError("Once set, the id value may not be changed.")
        else:
            self.ID=num
            self.ID_SET=True
    def save(self, manager, commit=True):
        if self.ID_SET==False:
            self.id=manager.inc()
        manager.root.other_set.add(self)
        if commit==True:
            transaction.commit()

class Set(Persistent):
    def __init__(self, ID=None, *items):
        Persistent.__init__(self)
        self.DS=OOTreeSet()
        if ID==None:
            self.ID=-1 #To give each object a unique id. The value, -1, is replaced automatically when saved by the project for the first time (which should be done right after the object is created).
            self.ID_SET=False
        else:
            if ID>=0:
                raise ValueError("Manual values should be negative.")
            self.ID=ID #You should remember what you’re putting here, and it should be negative.
            self.ID_SET=True
        self.update(items)
    def update(self, items):
        self.DS.update(items)
    def add(self, *items):
        self.DS.update(items)
    def remove(self, *items):
        for x in items:
            self.DS.remove(x)
    def has(self, *items):
        for x in items:
            if not self.DS.has_key(x):
                return False
        return True
    def __len__(self):
        return len(self.DS)
    def __iadd__(self, other):
        self.DS.update(other)
    def __isub__(self, other):
        self.remove(*other)
    def __contains__(self, other):
        return self.DS.has_key(other)
    def __iter__(self):
        return iter(self.DS)
    def __eq__(self, other):
        return self.id==other.id
    def __ne__(self, other):
        return self.id!=other.id
    def __hash__(self):
        return self.id
    def __lt__(self, other):
        return self.id<other.id
    def __le__(self, other):
        return self.id<=other.id
    def __gt__(self, other):
        return self.id>other.id
    def __ge__(self, other):
        return self.id>=other.id
    @property
    def id(self):
        if self.ID_SET==False:
            print("Warning. self.id_set is False. You are accessing an id that has not been set.")
        return self.ID
    @id.setter
    def id(self, num):
        if self.ID_SET==True:
            raise ValueError("Once set, the id value may not be changed.")
        else:
            self.ID=num
            self.ID_SET=True
    def save(self, manager, commit=True):
        if self.ID_SET==False:
            self.id=manager.inc()
        manager.root.other_set.add(self)
        if commit==True:
            transaction.commit()

class Counter(Persistent):
    #This is for creating a persistent id count object (using a plain integer outside of a class doesn't seem to work).
    def __init__(self, value=0):
        self.value=value
        self.ID_SET=False
        self.id=value
    #The following methods are so it will fit fine in a BTree (they don't have anything to do with self.value)
    def __eq__(self, other):
        return self.id==other.id
    def __ne__(self, other):
        return self.id!=other.id
    def __hash__(self):
        return self.id
    def __lt__(self, other):
        return self.id<other.id
    def __le__(self, other):
        return self.id<=other.id
    def __gt__(self, other):
        return self.id>other.id
    def __ge__(self, other):
        return self.id>=other.id
    @property
    def id(self):
        if self.ID_SET==False:
            print("Warning. self.id_set is False. You are accessing an id that has not been set.")
        return self.ID
    @id.setter
    def id(self, num):
        if self.ID_SET==True:
            raise ValueError("Once set, the id value may not be changed.")
        else:
            self.ID=num
            self.ID_SET=True

class Manager:
    def __init__(self, filepath):
        self.filepath=filepath
        self.storage = ZODB.FileStorage.FileStorage(filepath)
        self.db = ZODB.DB(self.storage)
        self.conn = self.db.open()
        self.root = self.conn.root
        print("Database opened.\n")
        try:
            self.root.other_dict #This holds arbitrary stuff, like the Counter. String keys.
        except AttributeError:
            self.root.other_dict=OOBTree()
            self.root.other_dict["id_count"]=Counter()
        try:
            self.root.other_set #set other
        except AttributeError:
            self.root.other_set=OOTreeSet() #This holds all our Btree and Set objects (they are put here when saved to help them be persistent).
    def inc(self): #This increments our Counter and returns the new value to become the integer id of a new object.
        self.root.other_dict["id_count"].value+=1
        return self.root.other_dict["id_count"].value
    def close(self):
        self.db.pack()
        self.db.close()
        print("\nDatabase closed.")

class Btree2(Btree):
    #To prove that we can inherit our own classes we created that inherit Persistent (but inheriting OOBTree or OOTreeSet causes issues)
    def __init__(self, ID=None, **attr):
        Btree.__init__(self, ID, **attr)




m=Manager("/path/to/database/test.fs")

try:
    m.root.tree #Causes an AttributeError if this is the first time you ran the program, because it doesn't exist.
    print("OOBTree loaded.")
except AttributeError:
    print("Creating OOBTree.")
    m.root.tree=OOBTree()
    for i in range(5):
        key=Btree2()
        key.save(m, commit=False) #Saving without committing adds it to the manager's OOBTree and gives it an integer ID. This needs to be done right after creating an object (whether or not you commit).
        value=Btree2()
        value.save(m, commit=False)
        m.root.tree[key]=value #Assigning key and value (which are both objects) to the OOBTree
    transaction.commit() #Commit the transactions

try:
    m.root.set
    print("OOTreeSet loaded.")
except AttributeError:
    print("Creating OOTreeSet")
    m.root.set=OOTreeSet()
    for i in range(5):
        item=Set()
        item.save(m, commit=False)
        m.root.set.add(item)
    transaction.commit()

#Doing the same with an OOTreeSet (since objects in them suffered from the same problem as objects as keys in an OOBTree)
for x in m.root.tree:
    print("Key: "+str(x.id))
    print("Value: "+str(m.root.tree[x].id))
    if x in m.root.tree:
        print("Comparison works for "+str(x.id))

print("\nOn to OOTreeSet.\n")

for x in m.root.set:
    if x in m.root.set:
        print("Comparison works for "+str(x.id))

m.close()

在ZOBD OOBTree中使用对象作为键的正确方法是什么？

2 个答案: