Query for documents where array size is greater than 1

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 3.2+):

// index for at least two name array elementsdb.accommodations.createIndex(    {'name.1': 1},    {partialFilterExpression: {'name.1': {$exists: true}}});

Update:

For mongodb versions 2.2+ more efficient way to do this described by @JohnnyHK in another answer.

1.Using $where

db.accommodations.find( { $where: "this.name.length > 1" } );

But...

Javascript executes more slowly than the native operators listed on this page, but is very flexible. See the server-side processing page for more information.

2.Create extra field NamesArrayLength, update it with names array length and then use in queries:

db.accommodations.find({"NamesArrayLength": {$gt: 1} });

It will be better solution, and will work much faster (you can create index on it).

I believe this is the fastest query that answers your question, because it doesn't use an interpreted $where clause:

{$nor: [    {name: {$exists: false}},    {name: {$size: 0}},    {name: {$size: 1}}]}

It means "all documents except those without a name (either non existant or empty array) or with just one name."

Test:

> db.test.save({})> db.test.save({name: []})> db.test.save({name: ['George']})> db.test.save({name: ['George', 'Raymond']})> db.test.save({name: ['George', 'Raymond', 'Richard']})> db.test.save({name: ['George', 'Raymond', 'Richard', 'Martin']})> db.test.find({$nor: [{name: {$exists: false}}, {name: {$size: 0}}, {name: {$size: 1}}]}){ "_id" : ObjectId("511907e3fb13145a3d2e225b"), "name" : [ "George", "Raymond" ] }{ "_id" : ObjectId("511907e3fb13145a3d2e225c"), "name" : [ "George", "Raymond", "Richard" ] }{ "_id" : ObjectId("511907e3fb13145a3d2e225d"), "name" : [ "George", "Raymond", "Richard", "Martin" ] }>