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MongoDB query to find property of first element of array?
You can use $slice operator for this. Let us first create a collection with documents −
> db.firstElementOfArray.insertOne(
... {
... _id: 100,
... "Details": [
... {
... "CustomerName": "John",
... "CustomerCountryName":"US"
... }
... ]
... }
... );
{ "acknowledged" : true, "insertedId" : 100 }
> db.firstElementOfArray.insertOne(
... {
... _id: 101,
... "Details": [
... {
... "CustomerName": "Carol",
... "CustomerCountryName":"UK"
... },
... {
... "CustomerName": "David",
... "CustomerCountryName":"AUS"
... }
... ]
... }
... );
{ "acknowledged" : true, "insertedId" : 101 }Following is the query to display all documents from the collection with the help of find() method −
> db.firstElementOfArray.find().pretty();
This will produce the following output −
{
"_id" : 100,
"Details" : [
{
"CustomerName" : "John",
"CustomerCountryName" : "US"
}
]
}
{
"_id" : 101,
"Details" : [
{
"CustomerName" : "Carol",
"CustomerCountryName" : "UK"
},
{
"CustomerName" : "David",
"CustomerCountryName" : "AUS"
}
]
}Following is the query to find property of first element of array −
> db.firstElementOfArray.find({},{'Details':{$slice:1},'Details.CustomerName':1}).pretty();This will produce the following output −
{ "_id" : 100, "Details" : [ { "CustomerName" : "John" } ] }
{ "_id" : 101, "Details" : [ { "CustomerName" : "Carol" } ] }
Updated on: 30-Jul-2019
840 Views
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