Upserts can create duplicate documents, unless there is a unique index to prevent duplicates. Consider an example where no document with the name Andy exists and multiple clients issue the following command at roughly the same time: db.runCommand( { update: "people", updates: [ { q: { name...
// the type of _id is `Number`"probability":1,// all documents had an _id field"hasDuplicates":false,// therefore no duplicates"types":[// an array of Type objects, @see `./lib/types
The combined results from the previous stage and the $unionWith stage can include duplicates. For example, create a suppliers collection and a warehouses collection: db.suppliers.insertMany([ { _id: 1, supplier: "Aardvark and Sons", state: "Texas" }, { _id: 2, supplier: "Bears Run Amo...
WriteResult({"nInserted":1}) > db.highsea.insert({"_id":"3","email":"644494365@qq.com"}) WriteResult({"nInserted":0,"writeError": {"code":11000,"errmsg":"insertDocument :: caused by :: 11000 E11000 duplicat e key error index: highsea.highsea.$_id_ dup key: { : \"3\" ...
If you use a persistent datastore without theautoloadoption, you need to callloadDatabasemanually. This function fetches the data from datafile and prepares the database.Don't forget it!If you use a persistent datastore, no command (insert, find, update, remove) will be executed beforeloadData...
Open up books/pipelines.py again and add the logic necessary to check for duplicates based on a new unique id field that you’ll derive from hashing the individual page URL:Python books/pipelines.py 1import hashlib 2import pymongo 3from itemadapter import ItemAdapter 4from scrapy.exceptions ...
1. _id: The_idfield represents a unique value in the MongoDB document. The_idfield is like the document's primary key. If you create a new document without an_idfield, MongoDB will automatically create the field. 2. Collection: This is a grouping of MongoDB documents. A collection is...
This also drastically increases complexity, duplicates data across multiple data stores and does not allow for real-time analytics 3. If available, writing native MapReduce operations within the NoSQL database itself MongoDB provides the Aggregation Pipeline natively within the database, which delivers...
db.persons.copyTo(newColl) - duplicates collection by copying all documents to newColl; no indexes are copied. db.persons.convertToCapped(maxBytes) - calls {convertToCapped:'persons', size:maxBytes}} command db.persons.dataSize() db.persons.distinct( key ) - e.g. db.persons.distinct( '...
1. _id: The_idfield represents a unique value in the MongoDB document. The_idfield is like the document's primary key. If you create a new document without an_idfield, MongoDB will automatically create the field. 2. Collection: This is a grouping of MongoDB documents. A collection is...