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Set filtering conditions for nested array in MongoDB
To set filtering conditions, use $filter and $cond in MongoDB aggregate(). The $filter selects a subset of an array to return based on the specified condition. Let us create a collection with documents −
> db.demo725.insertOne( ... { ... ... "details": { ... ... "userMessages": [ ... { ... "Messages": [ ... { "Message": "Hello" }, ... { "Message": "How" }, ... { "Message": "are" } ... ] ... ... }, ... { ... "Messages": [ ... { "Message": "Good" }, ... { "Message": "Bye" } ... ... ] ... }, ... { ... "Messages": [ ... { "Message": "Hello" }, ... { "Message": "Bye" } ... ... ] ... ... } ... ] ... } ... } ... ); { "acknowledged" : true, "insertedId" : ObjectId("5eab16cd43417811278f5893") }
Display all documents from a collection with the help of find() method −
> db.demo725.find();
This will produce the following output −
{ "_id" : ObjectId("5eab16cd43417811278f5893"), "details" : { "userMessages" : [ { "Messages" : [ { "Message" : "Hello" }, { "Message" : "How" }, { "Message" : "are" } ] }, { "Messages" : [ { "Message" : "Good" }, { "Message" : "Bye" } ] }, { "Messages" : [ { "Message" : "Hello" }, { "Message" : "Bye" } ] } ] } }
Following is the query to set filtering conditions for nested array −
> db.demo725.aggregate([ ... { ... $addFields: { ... "details.userMessages": { ... $filter: { ... input: "$details.userMessages", ... as: "out", ... cond: { ... $anyElementTrue: { ... $map: { ... input: "$$out.Messages", ... in: { $gte: [ { $indexOfBytes: [ "$$this.Message", "Hello" ] }, 0 ] } ... } ... } ... } ... } ... } ... } ... } ... ]).pretty()
This will produce the following output −
{ "_id" : ObjectId("5eab16cd43417811278f5893"), "details" : { "userMessages" : [ { "Messages" : [ { "Message" : "Hello" }, { "Message" : "How" }, { "Message" : "are" } ] }, { "Messages" : [ { "Message" : "Hello" }, { "Message" : "Bye" } ] } ] } }
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