mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-05-15 21:27:23 -04:00
Mike Bayer
9f6b67a37e
For a 1.4 / 1.3 merge, rewrite the documentation for Query.join() to indicate calling forms that are now considered legacy, including the use of strings in join(), sending a series of join paths in one call, and using the aliased=True flag. update the elementtree examples as well to use aliased() (they are much simpler to understand this way too) and update other links. Also improve docs for aliased() and some other ORM targets such as PropComparator. Change-Id: I636e3a9130dc5509e51c2cf60a52f38fcadffbc6 References: #4705
300 lines
8.6 KiB
Python
300 lines
8.6 KiB
Python
"""Uses the same strategy as
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``adjacency_list.py``, but associates each DOM row with its owning
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document row, so that a full document of DOM nodes can be loaded
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using O(1) queries - the construction of the "hierarchy" is performed
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after the load in a non-recursive fashion and is more
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efficient.
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"""
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# PART I - Imports/Configuration
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from __future__ import print_function
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import os
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import re
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from xml.etree import ElementTree
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from sqlalchemy import and_
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from sqlalchemy import Column
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from sqlalchemy import create_engine
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from sqlalchemy import ForeignKey
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from sqlalchemy import Integer
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from sqlalchemy import MetaData
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from sqlalchemy import String
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from sqlalchemy import Table
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from sqlalchemy import Unicode
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from sqlalchemy.orm import aliased
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from sqlalchemy.orm import lazyload
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from sqlalchemy.orm import mapper
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from sqlalchemy.orm import relationship
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from sqlalchemy.orm import Session
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e = create_engine("sqlite://")
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meta = MetaData()
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# PART II - Table Metadata
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# stores a top level record of an XML document.
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documents = Table(
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"documents",
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meta,
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Column("document_id", Integer, primary_key=True),
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Column("filename", String(30), unique=True),
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)
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# stores XML nodes in an adjacency list model. This corresponds to
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# Element and SubElement objects.
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elements = Table(
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"elements",
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meta,
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Column("element_id", Integer, primary_key=True),
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Column("parent_id", Integer, ForeignKey("elements.element_id")),
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Column("document_id", Integer, ForeignKey("documents.document_id")),
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Column("tag", Unicode(30), nullable=False),
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Column("text", Unicode),
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Column("tail", Unicode),
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)
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# stores attributes. This corresponds to the dictionary of attributes
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# stored by an Element or SubElement.
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attributes = Table(
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"attributes",
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meta,
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Column(
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"element_id",
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Integer,
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ForeignKey("elements.element_id"),
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primary_key=True,
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),
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Column("name", Unicode(100), nullable=False, primary_key=True),
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Column("value", Unicode(255)),
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)
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meta.create_all(e)
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# PART III - Model
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# our document class. contains a string name,
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# and the ElementTree root element.
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class Document(object):
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def __init__(self, name, element):
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self.filename = name
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self.element = element
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# PART IV - Persistence Mapping
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# Node class. a non-public class which will represent the DB-persisted
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# Element/SubElement object. We cannot create mappers for ElementTree elements
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# directly because they are at the very least not new-style classes, and also
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# may be backed by native implementations. so here we construct an adapter.
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class _Node(object):
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pass
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# Attribute class. also internal, this will represent the key/value attributes
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# stored for a particular Node.
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class _Attribute(object):
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def __init__(self, name, value):
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self.name = name
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self.value = value
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# setup mappers. Document will eagerly load a list of _Node objects.
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# they will be ordered in primary key/insert order, so that we can reconstruct
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# an ElementTree structure from the list.
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mapper(
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Document,
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documents,
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properties={
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"_nodes": relationship(
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_Node, lazy="joined", cascade="all, delete-orphan"
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)
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},
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)
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# the _Node objects change the way they load so that a list of _Nodes will
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# organize themselves hierarchically using the ElementTreeMarshal. this
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# depends on the ordering of nodes being hierarchical as well; relationship()
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# always applies at least ROWID/primary key ordering to rows which will
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# suffice.
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mapper(
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_Node,
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elements,
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properties={
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"children": relationship(
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_Node, lazy=None
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), # doesnt load; used only for the save relationship
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"attributes": relationship(
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_Attribute, lazy="joined", cascade="all, delete-orphan"
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), # eagerly load attributes
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},
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)
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mapper(_Attribute, attributes)
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# define marshalling functions that convert from _Node/_Attribute to/from
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# ElementTree objects. this will set the ElementTree element as
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# "document._element", and append the root _Node object to the "_nodes" mapped
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# collection.
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class ElementTreeMarshal(object):
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def __get__(self, document, owner):
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if document is None:
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return self
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if hasattr(document, "_element"):
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return document._element
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nodes = {}
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root = None
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for node in document._nodes:
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if node.parent_id is not None:
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parent = nodes[node.parent_id]
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elem = ElementTree.SubElement(parent, node.tag)
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nodes[node.element_id] = elem
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else:
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parent = None
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elem = root = ElementTree.Element(node.tag)
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nodes[node.element_id] = root
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for attr in node.attributes:
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elem.attrib[attr.name] = attr.value
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elem.text = node.text
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elem.tail = node.tail
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document._element = ElementTree.ElementTree(root)
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return document._element
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def __set__(self, document, element):
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def traverse(node):
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n = _Node()
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n.tag = str(node.tag)
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n.text = str(node.text)
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n.tail = str(node.tail)
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document._nodes.append(n)
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n.children = [traverse(n2) for n2 in node]
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n.attributes = [
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_Attribute(str(k), str(v)) for k, v in node.attrib.items()
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]
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return n
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traverse(element.getroot())
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document._element = element
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def __delete__(self, document):
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del document._element
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document._nodes = []
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# override Document's "element" attribute with the marshaller.
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Document.element = ElementTreeMarshal()
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# PART V - Basic Persistence Example
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line = "\n--------------------------------------------------------"
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# save to DB
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session = Session(e)
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# get ElementTree documents
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for file in ("test.xml", "test2.xml", "test3.xml"):
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filename = os.path.join(os.path.dirname(__file__), file)
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doc = ElementTree.parse(filename)
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session.add(Document(file, doc))
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print("\nSaving three documents...", line)
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session.commit()
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print("Done.")
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print("\nFull text of document 'text.xml':", line)
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document = session.query(Document).filter_by(filename="test.xml").first()
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ElementTree.dump(document.element)
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# PART VI - Searching for Paths
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# manually search for a document which contains "/somefile/header/field1:hi"
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print("\nManual search for /somefile/header/field1=='hi':", line)
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root = aliased(_Node)
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child_node = aliased(_Node)
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grandchild_node = aliased(_Node)
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d = (
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session.query(Document)
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.join(Document._nodes.of_type(root))
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.filter(and_(root.parent_id.is_(None), root.tag == "somefile"))
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.join(root.children.of_type(child_node))
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.filter(child_node.tag == "header")
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.join(child_node.children.of_type(grandchild_node))
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.filter(
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and_(grandchild_node.tag == "field1", grandchild_node.text == "hi")
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)
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.one()
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)
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ElementTree.dump(d.element)
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# generalize the above approach into an extremely impoverished xpath function:
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def find_document(path, compareto):
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query = session.query(Document)
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for i, match in enumerate(
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re.finditer(r"/([\w_]+)(?:\[@([\w_]+)(?:=(.*))?\])?", path)
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):
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(token, attrname, attrvalue) = match.group(1, 2, 3)
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if not i:
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parent = Document
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target_node = aliased(_Node)
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query = query.join(parent._nodes.of_type(target_node)).filter(
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target_node.parent_id.is_(None)
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)
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else:
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parent = target_node
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target_node = aliased(_Node)
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query = query.join(parent.children.of_type(target_node))
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query = query.filter(target_node.tag == token)
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if attrname:
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attribute_entity = aliased(_Attribute)
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query = query.join(
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target_node.attributes.of_type(attribute_entity)
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)
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if attrvalue:
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query = query.filter(
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and_(
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attribute_entity.name == attrname,
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attribute_entity.value == attrvalue,
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)
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)
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else:
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query = query.filter(attribute_entity.name == attrname)
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return (
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query.options(lazyload(Document._nodes))
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.filter(target_node.text == compareto)
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.all()
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)
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for path, compareto in (
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("/somefile/header/field1", "hi"),
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("/somefile/field1", "hi"),
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("/somefile/header/field2", "there"),
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("/somefile/header/field2[@attr=foo]", "there"),
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):
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print("\nDocuments containing '%s=%s':" % (path, compareto), line)
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print([d.filename for d in find_document(path, compareto)])
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