MongoDB updating Data

MongoDB updating Data

>$set Operator
this is used to add update an existing field or add a new field
Sysntax : db.collection.updateOne/updateMany({--findQuery--},{$set:{fieldName:"value"}})


> $inc Operator for Increment and Decrement 
this isus ed to increment / decrement the value 
Systax : db.collection.updateOne/updateMany({--findQuery--},{$set:{fieldName:"value"} , $inc:{age: INCREMENT_VALUE}})
Note: $inc can be combined with other operator
IMP : You can not put $set and $inc on same field , it will throw an error ie updating and incrementing age will cause an error 

>$min , $max , $mul
min is used to update field only when if specified value is less than the field value
max is used to update field only when if specified value is more than the field value
mul will multiply the field value 

>$unset 
this is used to delete field from a document 
let supose we want to delete phone number from document where isSporty is true 
db.userdata.updateMany({isSporty:true},{$unset:{phone:""}})

$rename
this is used to rename a field
Syntax: db.collection.updateMany({--find--},{$rename:{fieldName:"newFieldName"}})

>upsert
this is he third argument passed while updating a document 
this will update document if it exist or it will create a document 

db.userdata.update({name:"Abhinay"},{$set:{age:24,hobbies:[{title:"Yoga",frequency:2}]}},{upsert:true})

this will add user Abhinay as this does not exists, 
Importent :  upsert will not only update field value but also it has power to update field name ie there is no need of $rename field
with upsert , as it is inserting a new document

>updating Array
the problem : with the help of elemMatch we can get the desired array,,,, but how to accesss perticular element of an array
Solution we use $ for that  but remmeber we get only first element with $ to get specefic element we must use an identifier with $
example we want to update and array where title is sports and frequency is more than 2 
we can get array bu find query as db.userdata.find({hobbies:{$elemMatch:{title:"Sports",frequency:{$gt:2}}}}).pretty()
now to access perticular field we use $ as below 
 db.userdata.updateMany({hobbies:{$elemMatch:{title:"Sports",frequency:{$gt:2}}}}, {$set:{"hobbies.$.isHighFrequency":true}})
 
> Updating Sepcefic elemtn with $ and Identifier and condition
when we want to apply condition to filter result then we use an idetifier , a condition and $
let suppose we found frequency greater than 3 in this case we will have multple document within array some of them satisfying condition 
some not. now we want to filter them out who satisfy the condition for that we place an identifier then we apply condition in 
"arrayFilters"

db.userdata.updateMany(
{"hobbies.frequency":{$gt:2}}, >> find condition
{$set:{"hobbies.$[el].goodFrequency":true}}, >> update with only identifier "el"
{arrayFilters:[{"el.frequency":{$gt:2}}]}   >> condition on el 
)

> updating all items with $[]
this is used when we want to update all the fields within an array documents
example increment all the frequency of document which have age greater than 30 

db.userdata.updateMany({"age":{$gt:30}},{$inc:{"hobbies.$[].frequency":1}})

> updating first element 
this wil only work when there is condition is on the array fields
db.userdata.updateMany({"age":{$gt:30}},{$inc:{"hobbies.$.frequency":1}})     >> this will throw an error where as 
 db.userdata.updateMany({"hobbies.frequency":{$gt:5}},{$set:{"hobbies.$.nota":true}})   >> this will work as ther is a condition on 
 array, by appkyting condition to array we get a palceholder so we use $ to access first matching element of an array
 
> Adding an element to an array [use $push]
we learned how to update an document within an array Also we added new fields to an array document.
Now we will learn how to add entire document to an array 
db.userdata.updateOne({name:"Abhinay"},{$push:{hobbies:{title:"Sports",frequency:3}}})

>Add multiple element $each
db.userdata.updateOne({name:"Abhinay"},{$push:{hobbies:
{$each :[{title:"Gaming",frequency:3},{title:"Running",frequency:3}]}}}
)

>Remove element from an array [$pull]
 this will remove all occurance of an element 
 db.userdata.updateOne({name:"Abhinay"},{$pull:{hobbies:{title:"Gaming"}}})
 
 > Removing Last element of an array [$pop]
 
 db.userdata.updateOne({name:"Chirs"},{$pop:{hobbies:-1}})  remove first element
 db.userdata.updateOne({name:"Chirs"},{$pop:{hobbies:1}})  remove last element
 
 > Adding Unique value to an array 
 we already have an operator for this $push then what is the difference ... ? 
 with $addToSet we can add unique element to an array
  db.userdata.updateOne({name:"Abhinay"},{$addToSet:{hobbies:{title:"Gaming",frequency:3}}})
  this will add unique records to an array
  
  "name" : "Abhinay",
        "age" : 33,
        "hobbies" : [
                {
                        "title" : "Yoga",
                        "frequency" : 2
                },
             
                {
                        "title" : "Yoga",
                        "frequency" : 3
                }
        ]
 

Above Yoga records are unique in the sense of different frequency