pymongo的一些操作

 参考:http://www.yiibai.com/mongodb/mongodb_drop_collection.html

http://www.cnblogs.com/zhouxuchen/p/5544227.html

pymongo的一些操作:

启动

sudo service mongod start

远程连接的时候, 配置mongodb.conf  (通过 $ whereis mongod  找到位置)    #bind_ip = 127.0.0.1    改为0.0.0.0  ,和django是一样的

数据库 聚集(1层)

#!/usr/bin/python
#coding=utf-8

import datetime,time
from pymongo import MongoClient

#连接到数据库
# client = MongoClient('localhost', 27017)
client = MongoClient("127.0.0.1", 27017)

#list all databases
print client.database_names()   #database list

#delete specific database
# client.drop_database('tieba')   #delete
# db = client['tieba']            #没有就新建

#list all collection names
print db.collection_names(include_system_collections=False)

#delete specific collection
#db["mycollection"].drop()

聚集下的item:增删改查(2层)

insert_one,增加一个item，如果你传递给insert_one()方法的参数不包含_id字段，MongoClient将自动添加这个字段并且生成一个ObjectId设置为这个字段的值。

 def insert_one(self, document, bypass_document_validation=False):
        """Insert a single document.

          >>> db.test.count({'x': 1})
          0
          >>> result = db.test.insert_one({'x': 1})
          >>> result.inserted_id
          ObjectId('54f112defba522406c9cc208')
          >>> db.test.find_one({'x': 1})
          {u'x': 1, u'_id': ObjectId('54f112defba522406c9cc208')}

        :Parameters:
          - `document`: The document to insert. Must be a mutable mapping
            type. If the document does not have an _id field one will be
            added automatically.
          - `bypass_document_validation`: (optional) If ``True``, allows the
            write to opt-out of document level validation. Default is
            ``False``.

insert_many,增加一个可循环的item

    def insert_many(self, documents, ordered=True,
                    bypass_document_validation=False):
        """Insert an iterable of documents.

          >>> db.test.count()
          0
          >>> result = db.test.insert_many([{'x': i} for i in range(2)])
          >>> result.inserted_ids
          [ObjectId('54f113fffba522406c9cc20e'), ObjectId('54f113fffba522406c9cc20f')]
          >>> db.test.count()
          2

        :Parameters:
          - `documents`: A iterable of documents to insert.
          - `ordered` (optional): If ``True`` (the default) documents will be
            inserted on the server serially, in the order provided. If an error
            occurs all remaining inserts are aborted. If ``False``, documents
            will be inserted on the server in arbitrary order, possibly in
            parallel, and all document inserts will be attempted.
          - `bypass_document_validation`: (optional) If ``True``, allows the
            write to opt-out of document level validation. Default is
            ``False``.

update_one,注意一些操作符,如$set,$unset,$inc ,设置,删除,加法,对字段的操作,upsert=True,没有就增加

更新顶级字段

如下操作将更新第一个符合name等于Juni这个条件的文档。使用$set操作符更新cuisine字段且将lastModified修改为当前日期。

result = db.restaurants.update_one(
    {"name": "Juni"},
    {
        "$set": {
            "cuisine": "American (New)"
        },
        "$currentDate": {"lastModified": True}
    }
)

更新嵌入式文档中的字段

要更新一个嵌入式文档中的字段，需要使用点操作符。当使用点操作符时，使用点操作符需要使用双引号将字段名包裹。下面的操作将更新address字段中的street值。

result = db.restaurants.update_one(
    {"restaurant_id": "41156888"},
    {"$set": {"address.street": "East 31st Street"}}
)

    def update_one(self, filter, update, upsert=False,
                   bypass_document_validation=False,
                   collation=None):
        """Update a single document matching the filter.

          >>> for doc in db.test.find():
          ...     print(doc)
          ...
          {u'x': 1, u'_id': 0}
          {u'x': 1, u'_id': 1}
          {u'x': 1, u'_id': 2}
          >>> result = db.test.update_one({'x': 1}, {'$inc': {'x': 3}})
          >>> result.matched_count
          1
          >>> result.modified_count
          1
          >>> for doc in db.test.find():
          ...     print(doc)
          ...
          {u'x': 4, u'_id': 0}
          {u'x': 1, u'_id': 1}
          {u'x': 1, u'_id': 2}

        :Parameters:
          - `filter`: A query that matches the document to update.
          - `update`: The modifications to apply.
          - `upsert` (optional): If ``True``, perform an insert if no documents
            match the filter.
          - `bypass_document_validation`: (optional) If ``True``, allows the
            write to opt-out of document level validation. Default is
            ``False``.
          - `collation` (optional): An instance of
            :class:`~pymongo.collation.Collation`. This option is only supported
            on MongoDB 3.4 and above.

update_many,更改了所有匹配的item

    def update_many(self, filter, update, upsert=False,
                    bypass_document_validation=False, collation=None):
        """Update one or more documents that match the filter.

          >>> for doc in db.test.find():
          ...     print(doc)
          ...
          {u'x': 1, u'_id': 0}
          {u'x': 1, u'_id': 1}
          {u'x': 1, u'_id': 2}
          >>> result = db.test.update_many({'x': 1}, {'$inc': {'x': 3}})
          >>> result.matched_count
          3
          >>> result.modified_count
          3
          >>> for doc in db.test.find():
          ...     print(doc)
          ...
          {u'x': 4, u'_id': 0}
          {u'x': 4, u'_id': 1}
          {u'x': 4, u'_id': 2}

        :Parameters:
          - `filter`: A query that matches the documents to update.
          - `update`: The modifications to apply.
          - `upsert` (optional): If ``True``, perform an insert if no documents
            match the filter.
          - `bypass_document_validation` (optional): If ``True``, allows the
            write to opt-out of document level validation. Default is
            ``False``.
          - `collation` (optional): An instance of
            :class:`~pymongo.collation.Collation`. This option is only supported
            on MongoDB 3.4 and above.

replace_one,替换,这个是没有操作符的

替换一个文档

要替换整个文档（除了_id字段），将一个完整的文档作为第二个参数传给update()方法。替代文档对应原来的文档可以有不同的字段。在替代文档中，你可以忽略_id字段因为它是不变的。如果你包含了_id字段，那它必须和原文档的值相同。

重要：
在更新之后，该文档将只包含替代文档的字段。

在如下的更新操作后，被修改的文档将只剩下_id、name和address字段。该文档将不再包含restaurant_id、cuisine、grades以及borough字段。

result = db.restaurants.replace_one(
    {"restaurant_id": "41704620"},
    {
        "name": "Vella 2",
        "address": {
            "coord": [-73.9557413, 40.7720266],
            "building": "1480",
            "street": "2 Avenue",
            "zipcode": "10075"
        }
    }
)

 

    def replace_one(self, filter, replacement, upsert=False,
                    bypass_document_validation=False, collation=None):
        """Replace a single document matching the filter.

          >>> for doc in db.test.find({}):
          ...     print(doc)
          ...
          {u'x': 1, u'_id': ObjectId('54f4c5befba5220aa4d6dee7')}
          >>> result = db.test.replace_one({'x': 1}, {'y': 1})
          >>> result.matched_count
          1
          >>> result.modified_count
          1
          >>> for doc in db.test.find({}):
          ...     print(doc)
          ...
          {u'y': 1, u'_id': ObjectId('54f4c5befba5220aa4d6dee7')}

        The *upsert* option can be used to insert a new document if a matching
        document does not exist.

          >>> result = db.test.replace_one({'x': 1}, {'x': 1}, True)
          >>> result.matched_count
          0
          >>> result.modified_count
          0
          >>> result.upserted_id
          ObjectId('54f11e5c8891e756a6e1abd4')
          >>> db.test.find_one({'x': 1})
          {u'x': 1, u'_id': ObjectId('54f11e5c8891e756a6e1abd4')}

        :Parameters:
          - `filter`: A query that matches the document to replace.
          - `replacement`: The new document.
          - `upsert` (optional): If ``True``, perform an insert if no documents
            match the filter.
          - `bypass_document_validation`: (optional) If ``True``, allows the
            write to opt-out of document level validation. Default is
            ``False``.
          - `collation` (optional): An instance of
            :class:`~pymongo.collation.Collation`. This option is only supported
            on MongoDB 3.4 and above.

delete_one,删除一个item

"""Delete a single document matching the filter.

          >>> db.test.count({'x': 1})
          3
          >>> result = db.test.delete_one({'x': 1})
          >>> result.deleted_count
          1
          >>> db.test.count({'x': 1})
          2

        :Parameters:
          - `filter`: A query that matches the document to delete.
          - `collation` (optional): An instance of
            :class:`~pymongo.collation.Collation`. This option is only supported
            on MongoDB 3.4 and above.

delete_many,只要符合匹配规则的,都删除

要删除一个集合中的所有文档，给delete_many()方法传递一个空的条件参数即可。

result = db.restaurants.delete_many({})

销毁一个集合

删除所有文档的操作只会清空集合中的文档。该集合以及集合的索引将依旧存在。要清空一个集合，销毁该集合以及它的索引并且重建集合和索引可能是相比于清空一个集合更加高效的操作方式。使用drop()方法可以销毁一个集合，包括它所有的索引。

db.restaurants.drop()

 

    def delete_many(self, filter, collation=None):
        """Delete one or more documents matching the filter.

          >>> db.test.count({'x': 1})
          3
          >>> result = db.test.delete_many({'x': 1})
          >>> result.deleted_count
          3
          >>> db.test.count({'x': 1})
          0

        :Parameters:
          - `filter`: A query that matches the documents to delete.
          - `collation` (optional): An instance of
            :class:`~pymongo.collation.Collation`. This option is only supported
            on MongoDB 3.4 and above.

find_one

    def find_one(self, filter=None, *args, **kwargs):
        """Get a single document from the database.

        All arguments to :meth:`find` are also valid arguments for
        :meth:`find_one`, although any `limit` argument will be
        ignored. Returns a single document, or ``None`` if no matching
        document is found.

        The :meth:`find_one` method obeys the :attr:`read_preference` of
        this :class:`Collection`.

        :Parameters:

          - `filter` (optional): a dictionary specifying
            the query to be performed OR any other type to be used as
            the value for a query for ``"_id"``.

          - `*args` (optional): any additional positional arguments
            are the same as the arguments to :meth:`find`.

          - `**kwargs` (optional): any additional keyword arguments
            are the same as the arguments to :meth:`find`.

              >>> collection.find_one(max_time_ms=100)
        """

find,调用find()方式不传值即可得到集合中所有的文档,

cursor = db.restaurants.find()   

返回restaurants集合中所有文档。

如下所示的操作将查询borough字段等于Manhattan的文档。

cursor = db.restaurants.find({"borough": "Manhattan"})

逻辑与

你可以使用一个列表指定一个逻辑与条件查询操作，使用逗号分隔条件。

cursor = db.restaurants.find({"cuisine": "Italian", "address.zipcode": "10075"})

逻辑或

你可以使用$or操作符进行逻辑或条件的指定。

cursor = db.restaurants.find(
    {"$or": [{"cuisine": "Italian"}, {"address.zipcode": "10075"}]})

大于（$gt）操作符,操作符：$eq $gt $gte $in $lt $lte $ne $nin，等等，还有很多

查询字段grades包含一个嵌入式文档，其中score大于30。

cursor = db.restaurants.find({"grades.score": {"$gt": 30}})

对结果进行排序

要指定结果集的顺序，可以通过追加sort()方法进行查询。给sort()方法传递需要排序的字段和配需类型等。

• pymongo.ASCENDING表示升序排序。
• pymongo.DESCENDING表示降序排序。

如果要通过多个键星星排序，可以传递键的列表和以及对应的排序类型的列表。举例来说，如下操作将返回restaurants集合中所有的文档，并且先通过borough字段进行升序排序，然后在每个borough内，通过"address.zipcode"字段进行升序排序。

import pymongo
cursor = db.restaurants.find().sort([
    ("borough", pymongo.ASCENDING),
    ("address.zipcode", pymongo.ASCENDING)
])

 

"""Query the database.

        The `filter` argument is a prototype document that all results
        must match. For example:

        >>> db.test.find({"hello": "world"})

        only matches documents that have a key "hello" with value
        "world".  Matches can have other keys *in addition* to
        "hello". The `projection` argument is used to specify a subset
        of fields that should be included in the result documents. By
        limiting results to a certain subset of fields you can cut
        down on network traffic and decoding time.

        Raises :class:`TypeError` if any of the arguments are of
        improper type. Returns an instance of
        :class:`~pymongo.cursor.Cursor` corresponding to this query.

        The :meth:`find` method obeys the :attr:`read_preference` of
        this :class:`Collection`.

        :Parameters:
          - `filter` (optional): a SON object specifying elements which
            must be present for a document to be included in the
            result set
          - `projection` (optional): a list of field names that should be
            returned in the result set or a dict specifying the fields
            to include or exclude. If `projection` is a list "_id" will
            always be returned. Use a dict to exclude fields from
            the result (e.g. projection={'_id': False}).
          - `skip` (optional): the number of documents to omit (from
            the start of the result set) when returning the results
          - `limit` (optional): the maximum number of results to
            return
          - `no_cursor_timeout` (optional): if False (the default), any
            returned cursor is closed by the server after 10 minutes of
            inactivity. If set to True, the returned cursor will never
            time out on the server. Care should be taken to ensure that
            cursors with no_cursor_timeout turned on are properly closed.
          - `cursor_type` (optional): the type of cursor to return. The valid
            options are defined by :class:`~pymongo.cursor.CursorType`:

            - :attr:`~pymongo.cursor.CursorType.NON_TAILABLE` - the result of
              this find call will return a standard cursor over the result set.
            - :attr:`~pymongo.cursor.CursorType.TAILABLE` - the result of this
              find call will be a tailable cursor - tailable cursors are only
              for use with capped collections. They are not closed when the
              last data is retrieved but are kept open and the cursor location
              marks the final document position. If more data is received
              iteration of the cursor will continue from the last document
              received. For details, see the `tailable cursor documentation
              <http://www.mongodb.org/display/DOCS/Tailable+Cursors>`_.
            - :attr:`~pymongo.cursor.CursorType.TAILABLE_AWAIT` - the result
              of this find call will be a tailable cursor with the await flag
              set. The server will wait for a few seconds after returning the
              full result set so that it can capture and return additional data
              added during the query.
            - :attr:`~pymongo.cursor.CursorType.EXHAUST` - the result of this
              find call will be an exhaust cursor. MongoDB will stream batched
              results to the client without waiting for the client to request
              each batch, reducing latency. See notes on compatibility below.

          - `sort` (optional): a list of (key, direction) pairs
            specifying the sort order for this query. See
            :meth:`~pymongo.cursor.Cursor.sort` for details.
          - `allow_partial_results` (optional): if True, mongos will return
            partial results if some shards are down instead of returning an
            error.
          - `oplog_replay` (optional): If True, set the oplogReplay query
            flag.
          - `batch_size` (optional): Limits the number of documents returned in
            a single batch.
          - `manipulate` (optional): **DEPRECATED** - If True (the default),
            apply any outgoing SON manipulators before returning.
          - `collation` (optional): An instance of
            :class:`~pymongo.collation.Collation`. This option is only supported
            on MongoDB 3.4 and above.
          - `return_key` (optional): If True, return only the index keys in
            each document.
          - `show_record_id` (optional): If True, adds a field ``$recordId`` in
            each document with the storage engine's internal record identifier.
          - `snapshot` (optional): If True, prevents the cursor from returning
            a document more than once because of an intervening write
            operation.
          - `hint` (optional): An index, in the same format as passed to
            :meth:`~pymongo.collection.Collection.create_index` (e.g.
            ``[('field', ASCENDING)]``). Pass this as an alternative to calling
            :meth:`~pymongo.cursor.Cursor.hint` on the cursor to tell Mongo the
            proper index to use for the query.
          - `max_time_ms` (optional): Specifies a time limit for a query
            operation. If the specified time is exceeded, the operation will be
            aborted and :exc:`~pymongo.errors.ExecutionTimeout` is raised. Pass
            this as an alternative to calling
            :meth:`~pymongo.cursor.Cursor.max_time_ms` on the cursor.
          - `max_scan` (optional): The maximum number of documents to scan.
            Pass this as an alternative to calling
            :meth:`~pymongo.cursor.Cursor.max_scan` on the cursor.
          - `min` (optional): A list of field, limit pairs specifying the
            inclusive lower bound for all keys of a specific index in order.
            Pass this as an alternative to calling
            :meth:`~pymongo.cursor.Cursor.min` on the cursor.
          - `max` (optional): A list of field, limit pairs specifying the
            exclusive upper bound for all keys of a specific index in order.
            Pass this as an alternative to calling
            :meth:`~pymongo.cursor.Cursor.max` on the cursor.
          - `comment` (optional): A string or document. Pass this as an
            alternative to calling :meth:`~pymongo.cursor.Cursor.comment` on the
            cursor.
          - `modifiers` (optional): **DEPRECATED** - A dict specifying
            additional MongoDB query modifiers. Use the keyword arguments listed
            above instead.

        .. note:: There are a number of caveats to using
          :attr:`~pymongo.cursor.CursorType.EXHAUST` as cursor_type:

          - The `limit` option can not be used with an exhaust cursor.

          - Exhaust cursors are not supported by mongos and can not be
            used with a sharded cluster.

          - A :class:`~pymongo.cursor.Cursor` instance created with the
            :attr:`~pymongo.cursor.CursorType.EXHAUST` cursor_type requires an
            exclusive :class:`~socket.socket` connection to MongoDB. If the
            :class:`~pymongo.cursor.Cursor` is discarded without being
            completely iterated the underlying :class:`~socket.socket`
            connection will be closed and discarded without being returned to
            the connection pool.

find_one_and_delete

    def find_one_and_delete(self, filter,
                            projection=None, sort=None, **kwargs):
        """Finds a single document and deletes it, returning the document.

          >>> db.test.count({'x': 1})
          2
          >>> db.test.find_one_and_delete({'x': 1})
          {u'x': 1, u'_id': ObjectId('54f4e12bfba5220aa4d6dee8')}
          >>> db.test.count({'x': 1})
          1

        If multiple documents match *filter*, a *sort* can be applied.

          >>> for doc in db.test.find({'x': 1}):
          ...     print(doc)
          ...
          {u'x': 1, u'_id': 0}
          {u'x': 1, u'_id': 1}
          {u'x': 1, u'_id': 2}
          >>> db.test.find_one_and_delete(
          ...     {'x': 1}, sort=[('_id', pymongo.DESCENDING)])
          {u'x': 1, u'_id': 2}

        The *projection* option can be used to limit the fields returned.

          >>> db.test.find_one_and_delete({'x': 1}, projection={'_id': False})
          {u'x': 1}

        :Parameters:
          - `filter`: A query that matches the document to delete.
          - `projection` (optional): a list of field names that should be
            returned in the result document or a mapping specifying the fields
            to include or exclude. If `projection` is a list "_id" will
            always be returned. Use a mapping to exclude fields from
            the result (e.g. projection={'_id': False}).
          - `sort` (optional): a list of (key, direction) pairs
            specifying the sort order for the query. If multiple documents
            match the query, they are sorted and the first is deleted.
          - `**kwargs` (optional): additional command arguments can be passed
            as keyword arguments (for example maxTimeMS can be used with
            recent server versions).

find_one_and_replace

    def find_one_and_replace(self, filter, replacement,
                             projection=None, sort=None, upsert=False,
                             return_document=ReturnDocument.BEFORE, **kwargs):
        """Finds a single document and replaces it, returning either the
        original or the replaced document.

        The :meth:`find_one_and_replace` method differs from
        :meth:`find_one_and_update` by replacing the document matched by
        *filter*, rather than modifying the existing document.

          >>> for doc in db.test.find({}):
          ...     print(doc)
          ...
          {u'x': 1, u'_id': 0}
          {u'x': 1, u'_id': 1}
          {u'x': 1, u'_id': 2}
          >>> db.test.find_one_and_replace({'x': 1}, {'y': 1})
          {u'x': 1, u'_id': 0}
          >>> for doc in db.test.find({}):
          ...     print(doc)
          ...
          {u'y': 1, u'_id': 0}
          {u'x': 1, u'_id': 1}
          {u'x': 1, u'_id': 2}

        :Parameters:
          - `filter`: A query that matches the document to replace.
          - `replacement`: The replacement document.
          - `projection` (optional): A list of field names that should be
            returned in the result document or a mapping specifying the fields
            to include or exclude. If `projection` is a list "_id" will
            always be returned. Use a mapping to exclude fields from
            the result (e.g. projection={'_id': False}).
          - `sort` (optional): a list of (key, direction) pairs
            specifying the sort order for the query. If multiple documents
            match the query, they are sorted and the first is replaced.
          - `upsert` (optional): When ``True``, inserts a new document if no
            document matches the query. Defaults to ``False``.
          - `return_document`: If
            :attr:`ReturnDocument.BEFORE` (the default),
            returns the original document before it was replaced, or ``None``
            if no document matches. If
            :attr:`ReturnDocument.AFTER`, returns the replaced
            or inserted document.
          - `**kwargs` (optional): additional command arguments can be passed
            as keyword arguments (for example maxTimeMS can be used with
            recent server versions).

find_one_and_update

    def find_one_and_update(self, filter, update,
                            projection=None, sort=None, upsert=False,
                            return_document=ReturnDocument.BEFORE, **kwargs):
        """Finds a single document and updates it, returning either the
        original or the updated document.

          >>> db.test.find_one_and_update(
          ...    {'_id': 665}, {'$inc': {'count': 1}, '$set': {'done': True}})
          {u'_id': 665, u'done': False, u'count': 25}}

        By default :meth:`find_one_and_update` returns the original version of
        the document before the update was applied. To return the updated
        version of the document instead, use the *return_document* option.

          >>> from pymongo import ReturnDocument
          >>> db.example.find_one_and_update(
          ...     {'_id': 'userid'},
          ...     {'$inc': {'seq': 1}},
          ...     return_document=ReturnDocument.AFTER)
          {u'_id': u'userid', u'seq': 1}

        You can limit the fields returned with the *projection* option.

          >>> db.example.find_one_and_update(
          ...     {'_id': 'userid'},
          ...     {'$inc': {'seq': 1}},
          ...     projection={'seq': True, '_id': False},
          ...     return_document=ReturnDocument.AFTER)
          {u'seq': 2}

        The *upsert* option can be used to create the document if it doesn't
        already exist.

          >>> db.example.delete_many({}).deleted_count
          1
          >>> db.example.find_one_and_update(
          ...     {'_id': 'userid'},
          ...     {'$inc': {'seq': 1}},
          ...     projection={'seq': True, '_id': False},
          ...     upsert=True,
          ...     return_document=ReturnDocument.AFTER)
          {u'seq': 1}

        If multiple documents match *filter*, a *sort* can be applied.

          >>> for doc in db.test.find({'done': True}):
          ...     print(doc)
          ...
          {u'_id': 665, u'done': True, u'result': {u'count': 26}}
          {u'_id': 701, u'done': True, u'result': {u'count': 17}}
          >>> db.test.find_one_and_update(
          ...     {'done': True},
          ...     {'$set': {'final': True}},
          ...     sort=[('_id', pymongo.DESCENDING)])
          {u'_id': 701, u'done': True, u'result': {u'count': 17}}

        :Parameters:
          - `filter`: A query that matches the document to update.
          - `update`: The update operations to apply.
          - `projection` (optional): A list of field names that should be
            returned in the result document or a mapping specifying the fields
            to include or exclude. If `projection` is a list "_id" will
            always be returned. Use a dict to exclude fields from
            the result (e.g. projection={'_id': False}).
          - `sort` (optional): a list of (key, direction) pairs
            specifying the sort order for the query. If multiple documents
            match the query, they are sorted and the first is updated.
          - `upsert` (optional): When ``True``, inserts a new document if no
            document matches the query. Defaults to ``False``.
          - `return_document`: If
            :attr:`ReturnDocument.BEFORE` (the default),
            returns the original document before it was updated, or ``None``
            if no document matches. If
            :attr:`ReturnDocument.AFTER`, returns the updated
            or inserted document.
          - `**kwargs` (optional): additional command arguments can be passed
            as keyword arguments (for example maxTimeMS can be used with
            recent server versions).

 

3字段的一些操作(3层)

1.增加字段：collection.update({"_id":1},{"$set":{"new_field":0}}) #红色为查找条件，绿色为新增字段（当document中没有new_field这个字段时，则新增这个字段）

2.删除字段：collection.update({"_id":1},{"$unset":{"new_field":1}}) #红色为查找条件，绿色为删除字段

3.按条件查找：collection.find_one({"_id":1}) #红色为查找条件

                           collection.find({"_id":1})
4.统计不含有某一字段的记录数：dbName.collectionName.find({fieldName:null}).count()

5.求某字段最大值：collection.find().sort({"_id":-1}).limit(1)#得到的记录为集合中"_id"值最大的那一条