If you also have documents that don’t have the key, you can use: ME.find({ pictures: { $exists: true, $not: {$size: 0} } }) MongoDB doesn’t use indexes if $size is involved, so here is a better solution: ME.find({ pictures: { $exists: true, $ne: [] } }) If your property can have invalid values (like null … Read more
Lots of reads in every query, fewer regular writes Both databases perform well on reads where the hot data set fits in memory. Both also emphasize join-less data models (and encourage denormalization instead), and both provide indexes on documents or rows, although MongoDB’s indexes are currently more flexible. Cassandra’s storage engine provides constant-time writes no … Read more
You can do… JavaScript (shell): db.getCollectionNames() Node.js: db.listCollections() Non-JavaScript (shell only): show collections The reason I call that non-JavaScript is because: $ mongo prodmongo/app –eval “show collections” MongoDB shell version: 3.2.10 connecting to: prodmongo/app 2016-10-26T19:34:34.886-0400 E QUERY [thread1] SyntaxError: missing ; before statement @(shell eval):1:5 $ mongo prodmongo/app –eval “db.getCollectionNames()” MongoDB shell version: 3.2.10 connecting … Read more
There’s a more efficient way to do this in MongoDB 2.2+ now that you can use numeric array indexes (0 based) in query object keys. // Find all docs that have at least two name array elements. db.accommodations.find({‘name.1’: {$exists: true}}) You can support this query with an index that uses a partial filter expression (requires … Read more
Like this: mongo <dbname> –eval “db.dropDatabase()” More info on scripting the shell from the command line here: https://docs.mongodb.com/manual/tutorial/write-scripts-for-the-mongo-shell/#scripting