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MongoDB query with fields in the same document?
You can use $where operator for this. To understand the concept, let us create a collection with the document. The query to create a collection with a document is as follows −
> db.queryInSameDocumentsDemo.insertOne({"StudentDetails":{"StudentName":"John"},"NewStudentDetails":{"StudentName":"Carol"}});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90096ed3c9d04998abf017")
}
> db.queryInSameDocumentsDemo.insertOne({"StudentDetails":{"StudentName":"Bob"},"NewStudentDetails":{"StudentName":"Bob"}});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c900a435705caea966c5573")
}Display all documents from a collection with the help of find() method. The query is as follows −
> db.queryInSameDocumentsDemo.find().pretty();
The following is the output −
{
"_id" : ObjectId("5c90096ed3c9d04998abf017"),
"StudentDetails" : {
"StudentName" : "John"
},
"NewStudentDetails" : {
"StudentName" : "Carol"
}
}
{
"_id" : ObjectId("5c900a435705caea966c5573"),
"StudentDetails" : {
"StudentName" : "Bob"
},
"NewStudentDetails" : {
"StudentName" : "Bob"
}
}Case 1 − Here is the query with fields in the same document. We have used the equality (==) operator here. The query is as follows −
> db.queryInSameDocumentsDemo.find( { $where: "this.StudentDetails.StudentName == this.NewStudentDetails.StudentName" } ).pretty();The following is the output −
{
"_id" : ObjectId("5c900a435705caea966c5573"),
"StudentDetails" : {
"StudentName" : "Bob"
},
"NewStudentDetails" : {
"StudentName" : "Bob"
}
}Case 2 − Here is the query with fields in the same document. We have used not equal to operator.
The query is as follows −
> db.queryInSameDocumentsDemo.find( { $where: "this.StudentDetails.StudentName != this.NewStudentDetails.StudentName" } ).pretty();The following is the output −
{
"_id" : ObjectId("5c90096ed3c9d04998abf017"),
"StudentDetails" : {
"StudentName" : "John"
},
"NewStudentDetails" : {
"StudentName" : "Carol"
}
}
Updated on: 30-Jul-2019
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