Update elements inside a array MongoDB using Java

Question

A sample JSON Document

{
"_id" : "ab85cebc-8c7a-43bf-8efc-1151ccaa4f84",
"address" : {
    "city" : "Bangalore",
    "postcode" : "560080",
    "countrycode":"in",
    "street" : "SADASHIVNAGAR,SANKEY TANK RD"
},
"brand" : "Shell",
"prices" : [ 
    {
        "fuelType" : "DIESEL",
        "price" : 52.7
    }, 
    {
        "fuelType" : "PETROL",
        "price" : 67.05
    }
]
}

• I have around 20 docs for brand:Shell with different location in and around Bangalore.
• For all those I have to update Diesel and Petrol price.

Say current DIESEL and PETROL prices are 57.9 and 71.4 respectively?

How do I update all document with these latest price using JAVA (using Eclipse IDE)

Code (in complete)

public class UpdateGasstationFuelPrice {

public static void main(String[] args) {
    MongoClient client = new MongoClient("localhost",27017);
    MongoDatabase db = client.getDatabase( "notes" );

    MongoCursor<Document> cursor = db.getCollection( "gasstation" ).find( new BasicDBObject( "address.countrycode","in" )
        .append("address.city","Bangalore")
        .append("brand","Shell")).iterator();

    if (cursor.hasNext()){
        Document doc = cursor.next();
    }
    client.close();
}
}

Update with Query

  db.getCollection("gasstation").update({"address.countrycode":"in","address.city":"Bangalore","brand":"Shell"},   
            //Query to get the position
            { 
              "prices":  { $exists: true }  
            },
            // Use the positional $ operator to update specific element (which matches your query    
            { 
              $set: 
                  { 
                    //set value specific to elements field/key
                    "prices" : [
                        {
                            "fuelType" : "DIESEL",
                            "price" : 502.7
                        }, 
                        {
                            "fuelType" : "PETROL",
                            "price" : 607.05
                        }
                      ] 
                  } 
            } 
        );

Answer 1

You cannot updated util you know the position of the element which you want to update.

So basically what you can do is:

1. You need to query to seek the position.
2. Use the positional operator and update the array.

db.gasstation.update(    
    //Query to get the position
    { 
      "prices.fuelType":  "DIESEL"  
    },
    // Use the positional $ operator to update specific element (which matches your query    
    { 
      $set: 
          { 
            "prices.$" : 
              //Element/new value to update
               {
                 "fuelType" : "DIESEL",
                 "price" : 999.7
               } 
          } 
    } 
);

If you want just to update only specific field inside the json element embedded in the array you can do as follows:

db.gasstation.update(    
    //Query to get the position
    { 
      "prices.fuelType":  "DIESEL"  
    },
    // Use the positional $ operator to update specific element (which matches your query    
    { 
      $set: 
          { 
            //set value specific to elements field/key
            //i.e. Update documents in an Array
            "prices.$.price" : 999.7 
          } 
    } 
);

---

Updates based on comments:

db.gasstation.update(    
    //Query to match
    {
      "address.city":"Bangalore",
      "brand":"Shell",
      "countrycode":"in",
      "prices": { $exists: true }
    },
    // Use $set operator & overwrite entire array
    { 
      $set: 
          { 
            //Overwrite value
            "prices" : [
                {
                    "fuelType" : "DIESEL",
                    "price" : 502.7
                }, 
                {
                    "fuelType" : "PETROL",
                    "price" : 607.05
                }
              ] 
          } 
    } 
);