To update array in MongoDB document by variable index, use the below syntax. Here, yourIndexValue in the index value, where yourIndexVariableName is the variable name for index −
var yourIndexVariableName= yourIndexValue, anyVariableName= { "$set": {} }; yourVariableName["$set"]["yourFieldName."+yourIndexVariableName] = "yourValue"; db.yourCollectionName.update({ "_id": yourObjectId}, yourVariableName);
Let us first create a collection with documents −
> db.updateByVariableDemo.insertOne({"StudentSubjects":["MySQL","Java","SQL Server","PL/SQL"]}); { "acknowledged" : true, "insertedId" : ObjectId("5cd553c37924bb85b3f4893a") }
Following is the query to display all documents from a collection with the help of find() method −
> db.updateByVariableDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5cd553c37924bb85b3f4893a"), "StudentSubjects" : [ "MySQL", "Java", "SQL Server", "PL/SQL" ] }
Following is the query to update array in MongoDB document by variable index −
> var indexValue = 1, ... valueToUpdate= { "$set": {} }; > valueToUpdate["$set"]["StudentSubjects."+indexValue] = "MongoDB"; MongoDB > db.updateByVariableDemo.update({ "_id": ObjectId("5cd553c37924bb85b3f4893a") }, valueToUpdate) WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
Let us display the documents once again −
> db.updateByVariableDemo.find().pretty();
This will produce the following output −
{ "_id" : ObjectId("5cd553c37924bb85b3f4893a"), "StudentSubjects" : [ "MySQL", "MongoDB", "SQL Server", "PL/SQL" ] }