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Can the $in operator return null for unmatched documents?
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)
Data science time! April 2019 and salary with experience
The Ask Question Wizard is Live!How do I update/upsert a document in Mongoose?Query for documents where array size is greater than 1Find document with array that contains a specific valuemongodb: return an array of document idsHow do you query a MongoDB document where an array attribute is null or of zero length?Mongoose: findOneAndUpdate doesn't return updated documentMongoDB- Return Array of existing fields by compare collection with Array of objectmongoose findall return data from a different modelChecking that a field in Mongo contains multiple valuesHow to modify existing data or create new if doesn't exist in mongodb?
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I have a requirement to return the same length of the array provided to mongo.
usernames = ['user1', 'user2', 'user3']
Now lets say user3 doesn't exist, is there a way to return null when mongo doesn't find the document ?
If i'm using the $in operator i only get the matched documents ex.
User.find( username: $in: usernames )
result = [user1Document, user2Document]
I can loop over the array and query the database for every username but it's not efficient.
const userPromises = usernames.map(username => User.findOne( username ));
return Promise.all(userPromises);
mongodb mongoose
asked Mar 22 at 14:11
Asaf AvivAsaf Aviv
1,1031213
add a comment |
I have a requirement to return the same length of the array provided to mongo.
usernames = ['user1', 'user2', 'user3']
Now lets say user3 doesn't exist, is there a way to return null when mongo doesn't find the document ?
If i'm using the $in operator i only get the matched documents ex.
User.find( username: $in: usernames )
result = [user1Document, user2Document]
I can loop over the array and query the database for every username but it's not efficient.
const userPromises = usernames.map(username => User.findOne( username ));
return Promise.all(userPromises);
mongodb mongoose
asked Mar 22 at 14:11
Asaf AvivAsaf Aviv
1,1031213
1
You should use iteration to returnnullfor the non-existing elements as you did. Aggregation trick might help here but it is even more costly then the looping.
– Anthony Winzlet
Mar 22 at 14:24
add a comment |
I have a requirement to return the same length of the array provided to mongo.
usernames = ['user1', 'user2', 'user3']
Now lets say user3 doesn't exist, is there a way to return null when mongo doesn't find the document ?
If i'm using the $in operator i only get the matched documents ex.
User.find( username: $in: usernames )
result = [user1Document, user2Document]
I can loop over the array and query the database for every username but it's not efficient.
const userPromises = usernames.map(username => User.findOne( username ));
return Promise.all(userPromises);
mongodb mongoose
asked Mar 22 at 14:11
Asaf AvivAsaf Aviv
1,1031213
I have a requirement to return the same length of the array provided to mongo.
usernames = ['user1', 'user2', 'user3']
Now lets say user3 doesn't exist, is there a way to return null when mongo doesn't find the document ?
If i'm using the $in operator i only get the matched documents ex.
User.find( username: $in: usernames )
result = [user1Document, user2Document]
I can loop over the array and query the database for every username but it's not efficient.
const userPromises = usernames.map(username => User.findOne( username ));
return Promise.all(userPromises);
mongodb mongoose
mongodb mongoose
asked Mar 22 at 14:11
Asaf AvivAsaf Aviv
1,1031213
asked Mar 22 at 14:11
Asaf AvivAsaf Aviv
1,1031213
asked Mar 22 at 14:11
Asaf AvivAsaf Aviv
1,1031213
asked Mar 22 at 14:11
Asaf AvivAsaf Aviv
1,1031213
asked Mar 22 at 14:11
Asaf AvivAsaf Aviv
1,1031213
1,1031213
1
You should use iteration to returnnullfor the non-existing elements as you did. Aggregation trick might help here but it is even more costly then the looping.
– Anthony Winzlet
Mar 22 at 14:24
add a comment |
1
You should use iteration to returnnullfor the non-existing elements as you did. Aggregation trick might help here but it is even more costly then the looping.
– Anthony Winzlet
Mar 22 at 14:24
1
1
You should use iteration to return
null for the non-existing elements as you did. Aggregation trick might help here but it is even more costly then the looping.– Anthony Winzlet
Mar 22 at 14:24
You should use iteration to return
null for the non-existing elements as you did. Aggregation trick might help here but it is even more costly then the looping.– Anthony Winzlet
Mar 22 at 14:24
add a comment |
1 Answer
1
active
oldest
votes
You can start with initial filtering using $in and then to map all the values from input array into final result you have to $group them $push-ing $$ROOT (enitre document), then you can just merge input usernames with docs using $map and $filter operators:
db.col.aggregate([
$match: username: $in: ['user1', 'user2', 'user3']
,
$group:
_id: null,
docs: $push: "$$ROOT"
,
$project:
_id: 0,
results:
$map:
input: ['user1', 'user2', 'user3'],
as: 'username',
in:
$let:
vars:
filtered:
$filter:
input: "$docs",
as: "doc",
cond: $eq: [ "$$doc.username", "$$username" ]
,
in:
$arrayElemAt: [ "$$filtered", 0 ]
])
Mongo playground
answered Mar 22 at 14:23
micklmickl
16.4k61841
Perfect, Thank you!
– Asaf Aviv
Mar 22 at 14:42
How can i do the same operation with ObjectIds ? when i try to change username to _id i'm getting'_id' starts with an invalid character for a user variable name
– Asaf Aviv
Mar 22 at 15:19
@AsafAviv yes you can but I need to see your code to see why you're getting that error, please use mongo playground for that
– mickl
Mar 22 at 17:17
mongoplayground.net/p/Zep8U4aeKHx thanks again
– Asaf Aviv
Mar 22 at 17:50
1
Nice, Thank you for your time @mickl i appreciate it!
– Asaf Aviv
Mar 22 at 18:08
|
show 3 more comments
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1 Answer
1
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oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
You can start with initial filtering using $in and then to map all the values from input array into final result you have to $group them $push-ing $$ROOT (enitre document), then you can just merge input usernames with docs using $map and $filter operators:
db.col.aggregate([
$match: username: $in: ['user1', 'user2', 'user3']
,
$group:
_id: null,
docs: $push: "$$ROOT"
,
$project:
_id: 0,
results:
$map:
input: ['user1', 'user2', 'user3'],
as: 'username',
in:
$let:
vars:
filtered:
$filter:
input: "$docs",
as: "doc",
cond: $eq: [ "$$doc.username", "$$username" ]
,
in:
$arrayElemAt: [ "$$filtered", 0 ]
])
Mongo playground
answered Mar 22 at 14:23
micklmickl
16.4k61841
Perfect, Thank you!
– Asaf Aviv
Mar 22 at 14:42
How can i do the same operation with ObjectIds ? when i try to change username to _id i'm getting'_id' starts with an invalid character for a user variable name
– Asaf Aviv
Mar 22 at 15:19
@AsafAviv yes you can but I need to see your code to see why you're getting that error, please use mongo playground for that
– mickl
Mar 22 at 17:17
mongoplayground.net/p/Zep8U4aeKHx thanks again
– Asaf Aviv
Mar 22 at 17:50
1
Nice, Thank you for your time @mickl i appreciate it!
– Asaf Aviv
Mar 22 at 18:08
|
show 3 more comments
You can start with initial filtering using $in and then to map all the values from input array into final result you have to $group them $push-ing $$ROOT (enitre document), then you can just merge input usernames with docs using $map and $filter operators:
db.col.aggregate([
$match: username: $in: ['user1', 'user2', 'user3']
,
$group:
_id: null,
docs: $push: "$$ROOT"
,
$project:
_id: 0,
results:
$map:
input: ['user1', 'user2', 'user3'],
as: 'username',
in:
$let:
vars:
filtered:
$filter:
input: "$docs",
as: "doc",
cond: $eq: [ "$$doc.username", "$$username" ]
,
in:
$arrayElemAt: [ "$$filtered", 0 ]
])
Mongo playground
answered Mar 22 at 14:23
micklmickl
16.4k61841
Perfect, Thank you!
– Asaf Aviv
Mar 22 at 14:42
How can i do the same operation with ObjectIds ? when i try to change username to _id i'm getting'_id' starts with an invalid character for a user variable name
– Asaf Aviv
Mar 22 at 15:19
@AsafAviv yes you can but I need to see your code to see why you're getting that error, please use mongo playground for that
– mickl
Mar 22 at 17:17
mongoplayground.net/p/Zep8U4aeKHx thanks again
– Asaf Aviv
Mar 22 at 17:50
1
Nice, Thank you for your time @mickl i appreciate it!
– Asaf Aviv
Mar 22 at 18:08
|
show 3 more comments
You can start with initial filtering using $in and then to map all the values from input array into final result you have to $group them $push-ing $$ROOT (enitre document), then you can just merge input usernames with docs using $map and $filter operators:
db.col.aggregate([
$match: username: $in: ['user1', 'user2', 'user3']
,
$group:
_id: null,
docs: $push: "$$ROOT"
,
$project:
_id: 0,
results:
$map:
input: ['user1', 'user2', 'user3'],
as: 'username',
in:
$let:
vars:
filtered:
$filter:
input: "$docs",
as: "doc",
cond: $eq: [ "$$doc.username", "$$username" ]
,
in:
$arrayElemAt: [ "$$filtered", 0 ]
])
Mongo playground
answered Mar 22 at 14:23
micklmickl
16.4k61841
You can start with initial filtering using $in and then to map all the values from input array into final result you have to $group them $push-ing $$ROOT (enitre document), then you can just merge input usernames with docs using $map and $filter operators:
db.col.aggregate([
$match: username: $in: ['user1', 'user2', 'user3']
,
$group:
_id: null,
docs: $push: "$$ROOT"
,
$project:
_id: 0,
results:
$map:
input: ['user1', 'user2', 'user3'],
as: 'username',
in:
$let:
vars:
filtered:
$filter:
input: "$docs",
as: "doc",
cond: $eq: [ "$$doc.username", "$$username" ]
,
in:
$arrayElemAt: [ "$$filtered", 0 ]
])
Mongo playground
answered Mar 22 at 14:23
micklmickl
16.4k61841
answered Mar 22 at 14:23
micklmickl
16.4k61841
answered Mar 22 at 14:23
micklmickl
16.4k61841
answered Mar 22 at 14:23
micklmickl
16.4k61841
16.4k61841
Perfect, Thank you!
– Asaf Aviv
Mar 22 at 14:42
How can i do the same operation with ObjectIds ? when i try to change username to _id i'm getting'_id' starts with an invalid character for a user variable name
– Asaf Aviv
Mar 22 at 15:19
@AsafAviv yes you can but I need to see your code to see why you're getting that error, please use mongo playground for that
– mickl
Mar 22 at 17:17
mongoplayground.net/p/Zep8U4aeKHx thanks again
– Asaf Aviv
Mar 22 at 17:50
1
Nice, Thank you for your time @mickl i appreciate it!
– Asaf Aviv
Mar 22 at 18:08
|
show 3 more comments
Perfect, Thank you!
– Asaf Aviv
Mar 22 at 14:42
How can i do the same operation with ObjectIds ? when i try to change username to _id i'm getting'_id' starts with an invalid character for a user variable name
– Asaf Aviv
Mar 22 at 15:19
@AsafAviv yes you can but I need to see your code to see why you're getting that error, please use mongo playground for that
– mickl
Mar 22 at 17:17
mongoplayground.net/p/Zep8U4aeKHx thanks again
– Asaf Aviv
Mar 22 at 17:50
1
Nice, Thank you for your time @mickl i appreciate it!
– Asaf Aviv
Mar 22 at 18:08
Perfect, Thank you!
– Asaf Aviv
Mar 22 at 14:42
Perfect, Thank you!
– Asaf Aviv
Mar 22 at 14:42
How can i do the same operation with ObjectIds ? when i try to change username to _id i'm getting
'_id' starts with an invalid character for a user variable name– Asaf Aviv
Mar 22 at 15:19
How can i do the same operation with ObjectIds ? when i try to change username to _id i'm getting
'_id' starts with an invalid character for a user variable name– Asaf Aviv
Mar 22 at 15:19
@AsafAviv yes you can but I need to see your code to see why you're getting that error, please use mongo playground for that
– mickl
Mar 22 at 17:17
@AsafAviv yes you can but I need to see your code to see why you're getting that error, please use mongo playground for that
– mickl
Mar 22 at 17:17
mongoplayground.net/p/Zep8U4aeKHx thanks again
– Asaf Aviv
Mar 22 at 17:50
mongoplayground.net/p/Zep8U4aeKHx thanks again
– Asaf Aviv
Mar 22 at 17:50
1
1
Nice, Thank you for your time @mickl i appreciate it!
– Asaf Aviv
Mar 22 at 18:08
Nice, Thank you for your time @mickl i appreciate it!
– Asaf Aviv
Mar 22 at 18:08
|
show 3 more comments
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1
You should use iteration to return
nullfor the non-existing elements as you did. Aggregation trick might help here but it is even more costly then the looping.– Anthony Winzlet
Mar 22 at 14:24