How To Update Array
The $ operator acts as a placeholder for the first match of the update query document.
{
_id: 4,
grades: [
{ grade: 80, mean: 75, std: 8 },
{ grade: 85, mean: 90, std: 5 }, // 6
{ grade: 85, mean: 85, std: 8 }
]
}
db.students.updateOne(
{ _id: 4, "grades.grade": 85 },
{ $set: { "grades.$.std" : 6 } }
)
The $pop operator removes the first or last element of an array.
{
_id: 1,
scores: [ 8, 9, 10 ] // [ 9, 10 ]
}
db.students.updateOne( { _id: 1 }, { $pop: { scores: -1 } } )
The $pull operator removes from an array all instances of values that match a specified condition.
{
_id: 1,
votes: [ 3, 5, 6, 7, 7, 8 ] // [ 3, 5 ]
}
db.profiles.updateOne( { _id: 1 }, { $pull: { votes: { $gte: 6 } } } )
How To Shard Collection
// namespace: <database>.<collection>
// key: { <field1>: <1|"hashed"> }
// 1: ranged based sharding
// hashed: hashed based sharding
sh.shardCollection(namespace, key)