Find MongoDB records where array field is not empty

Solution 1:

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 boolean or others) , then you an add an additional check using $types as proposed in this answer:

With mongo >= 3.2:

ME.find({ pictures: { $exists: true, $type: 'array', $ne: [] } })

With mongo < 3.2:

ME.find({ pictures: { $exists: true, $type: 4, $ne: [] } })

Since the MongoDB 2.6 release, you can compare with the operator $gt, but this could lead to unexpected results (you can find a detailed explanation in this answer):

ME.find({ pictures: { $gt: [] } })

Solution 2:

After some more looking, especially in the mongodb documents, and puzzling bits together, this was the answer:

ME.find({pictures: {$exists: true, $not: {$size: 0}}})