Question

我正在使用图形对象映射，其中我有2个对象来表示2个节点。我想拥有关系的属性，如何定义与属性关系的类？ Here，我看到了一个例子，但没有使用对象。

我的代码如下：

class Intent(GraphObject):
   name = Property()
   message = RelatedTo("Message", "HAS")

class Message(GraphObject):
   name = Property()
   owner = RelatedFrom("Intent","HAS")

graph = Graph(password='1234')
intent = Intent()
intent.name = "ABC"
complete_intent = graph.pull(intent)

如果我想为关系提供一些属性＆＃34; HAS＆＃34;，如何定义类HAS？什么应该是从哪里继承的基类（比如节点的GraphObject，是否存在关系的东西？）

Answer 1

py2neo的当前版本不允许关联对象＆＃39;，这将允许您以标准OOP-y方式将参数放入关系中。

OGM对于开始项目和快速插入/检索事务非常有用，但对于大多数更复杂的事务，您将需要编写cypher来实现您的目标。

但是，您经常希望在GraphObject上组织这些查询，有时您可以扩展GraphObject以添加方法以提供一些必需的功能。

在您的使用案例中，您可能希望添加一些类似下面的方法来获取或设置您的关系属性。我已经编写了一个快速演示来检索关系的属性，你也可以添加一个类似的方法来设置关系。

from py2neo.ogm import (GraphObject,
                        INCOMING,
                        OUTGOING,
                        Property,
                        RelatedFrom,
                        RelatedTo,)
# this function makes this kind of thing tonnes easier
from py2neo.types import remote


class GraphObjectWithRelProps(GraphObject):
    """Simple extension to add get method for a relationship
    between self and another node"""

    @staticmethod
    def _get_relationship(source, target, relationship):
        """Returns the relationship connecting source and target as set
        in the class definition.
        Copy this method, adding an argument for the params
        and altering the cypher to add a set function

        Only works if two classes are rleated by only one relationship

        :param source: GraphObject instance - the starting node
        :param target: GraphObject instance - the ending node
        :param relationship: str name of the relationship on source"""

        # get relationship pattern
        rel = getattr(source, relationship)
        # the pattern is calculated for us on this object
        pattern = rel._RelatedObjects__relationship_pattern

        # basic cypher query
        q = ('MATCH {0} '
             'WHERE id(a) = $sId AND id(b) = $tId '
             'RETURN _').format(pattern)
        # for a set operation you would add 
        # DELETE _ CREATE {0} SET _ += $relParams
        # where $relParams is supplied as a dict with your params
        # you could also add a patch method using _ += $relParams
        # the remote function allows us to get a reference to the graph
        graph = remote(source.__ogm__.node).graph
        # as well as the node IDs of the GraphObject
        params = {
            'sId': remote(source.__ogm__.node)._id,
            'tId': remote(target.__ogm__.node)._id,
        }

        return graph.run(q, params).evaluate()


class Intent(GraphObjectWithRelProps):
    name = Property()
    message = RelatedTo("Message", "HAS")

    def get_message_rel(self, n):
        graph = remote(self.__ogm__.node).graph
        return self._get_relationship(graph, self, n, 'message')


class Message(GraphObjectWithRelProps):
    name = Property()
    owner = RelatedFrom("Intent","HAS")

    def get_owner_rel(self, n):
        graph = remote(self.__ogm__.node).graph
        return self._get_relationship(graph, self, n, 'owner')

py2neo：使用对象获取关系属性

1 个答案: