Paging
sort()
limit(numPerPage)
skip(page*numPerPage)
Basic Writes
Upsert == Insert + Update
insertOne()
insertMany()
const upsertResult = await theaters.updateOne(
{
"location.address": newTheaterDoc.location.address,
},
{
$set: newTheaterDoc,
},
{ upsert: true },
)
Write Concerns
严格的情况下，需要确保大多数写入成功再返回成功消息。
How they can provide different level of write durablilty in our application.
// w: num of nodes ack(ed)
writeConcern: {w:1}
- Only requests an acknowledgement that one node applied the write
- This is the default writeConcern in MongoDB
writeConcern: {w:"majority"}
0 does ensure that a write was committed by any nodes.
writeConcern: {w:0 }
Basic Updates
updateOne()
updateMany()
const upsertResult = await theaters.updateOne(
{
"location.address": newTheaterDoc.location.address,
},
{
$set: newTheaterDoc,
},
{ upsert: true },
)
Basic Joins
- Join two collections of data
- Movies and comments
- Use new expressive
$lookup - Build aggregation in Compass, and then export to language
Pipeline
[
{
'$match': {
'year': {
'$gte': 1980,
'$lt': 1990
}
}
},
{'$lookup': {
'from': 'comments',
'let': {
//
'id': '$_id'
},
'pipeline': [
{
'$match': {
'$expr': {
'$eq': [
'$movie_id', '$$id'
]
}
}
}, {
'$count': 'count'
}
],
'as': 'movie_comments'
}
}
]
The only way we can use fields from the movies collection in the pipeline is by defining those variables in the let expression.
Basic Deletes
When we perform a delete:
- Collection data will be changed
- Indexes will be updated
- Entries in the oplog(for replication) will be added
//deleteOne deletes the first matching document in $natural order.
deleteOne()
// deleteMany deletes multiple matching documents in one operation.
deleteMany()