Update property in nested array of entities in MongoDB

Question

Is there a straight forward way to update nested array of entities in MongoDB. I am using MongoDB C# Driver for making the DB call from application. Below is an exmaple : say I have a Student collection where each document has a nested array of Course with some necessary fields populated and Course by itself is a separate collection like:

{
 "_id": "234dssfcv456",
 "Name": "Jean Douglas",
 "Age": 32,
 "Courses": 
  [
    {
       "_id": "1234",
       "Name": "Computer Science",
       "Level": "Basic" 
    },
    {
       "_id": "3456",
       "Name": "Bio Science",
       "Level": "Intermediate" 
    }
  ] 
}

I know I can update the nested entity by index something like below but I don't know the index and rather know only the nested Course object Id only.

db.College.Student.update(
    {"Student._id": "234dssfcv456"}, 
    {$set: {
        "Student.$.Courses.1.Level": "Basic"
    }}

Right now, am reading the entire nested array of courses -> doing the modification at application end -> then passing the entire array for update with the filedname "Courses" which is going to replace the existing array with the one passed.

But was thinking, is there an way I can update one entity in array with the Id available. Please suggest.

*** On the right side in Related question section all shows updating the nested array of objects using the index of the object item which is not a possibility for me.

andrei.ciprian · Accepted Answer · 2016-08-11 15:20:32Z

22

Mongo shell:

> db.students.find( {_id:"234dssfcv456", "Courses._id":"1234"} ).pretty()
> db.students.update( {_id:"234dssfcv456", "Courses._id":"3456"}, { $set: { "Courses.$.Level" : "Updated" } } )

C# Mongo schema:

public class Student {
  [BsonId]
  [BsonRepresentation(BsonType.String)]
  public string Id { get; set; }
  public string Name { get; set; }
  public int Age { get; set; }
  public Course[] Courses { get; set; }
}

public class Course {
  [BsonId]
  [BsonRepresentation(BsonType.String)]
  public string Id { get; set; }
  public string Name { get; set; }
  public string Level { get; set; }
}

Lookup Mongo docs for the positional operator. With driver higher than version 2.2.3.3 I am using:

  var _client = new MongoClient(@"....");
  var _database = _client.GetDatabase("...");
  var _students =  _database.GetCollection<Student>("students");

  var filter = Builders<Student>.Filter;
  var studentIdAndCourseIdFilter = filter.And(
    filter.Eq(x => x.Id, "234dssfcv456"),
    filter.ElemMatch(x => x.Courses, c => c.Id == "1234") );
   // find student with id and course id
   var student = _students.Find(studentIdAndCourseIdFilter).SingleOrDefault();

  // update with positional operator
  var update = Builders<Student>.Update;      
  var courseLevelSetter = update.Set("Courses.$.Level", "Updated Level");
  _students.UpdateOne(studentIdAndCourseIdFilter, courseLevelSetter);

answered Aug 11, 2016 at 15:20

andrei.ciprian

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1 Comment

Rahul Over a year ago

Real nice answer. Appreciate your effort. Thanks mate :)

user7224827 · Accepted Answer · 2017-02-04 16:02:36Z

11

Instead of update.Set("Courses.$.Level", "Updated Level"); you can also do it like this:

update.Set(x => x.Courses[-1].Level, "Updated Level");

Source: http://www.mattburkedev.com/updating-inside-a-nested-array-with-the-mongodb-positional-operator-in-c-number/

answered Feb 4, 2017 at 16:02

user7224827

1 Comment

Rickchip Over a year ago

I know this is old and it helped me solve a similar problem. Taking it one step further, how would you update multiple Courses at the same time?

Matt Ghafouri · Accepted Answer · 2024-05-05 19:06:12Z

I also had the same question after too much investigation and came across a solution without being forced to use any magic string.

my object structure:

public class SettingDBEntity  
{
  [BsonRepresentation(BsonType.String)]
  public Guid Id { get; set; }

  public string Title { get; set; }

  public List<GoalDBEntity> Inputs { get; set; } = new();
}

public class InputDBEntity
{
  public byte Id { get; set; }

  public string? Title { get; set; }
  public string? Question { get; set; }

  public List<OutputDBEntity> Outputs { get; set; } = new();
 }


 public class OutputDBEntity
 {
  public byte Id { get; set; } 
  public string? Title { get; set; }
  public string? Note { get; set; } 
 }

Now to update just one specific output of a specific Input

var filter = Builders<SettingDBEntity>.Filter.And(
   Builders<SettingDBEntity>.Filter.Eq(r => r.Id, roadmapId), 
   Builders<SettingDBEntity>.Filter.ElemMatch(r => r.Inputs, g => g.Id == 
   inputId));


   var setter = Builders<SettingDBEntity>.Update.Set
         (s => s.Inputs[0].Outputs[outputParameter.Id], 
         CreateOutputObjcet(output));

   var updateResult = await Collection.UpdateOneAsync(filter, setter);

   if (updateResult.ModifiedCount != 1)
           throw new DatabaseException("");

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