MongoDb c# driver find item in array by field value

Question

i found the way to check is the value contains in simple array :

var filter = Builders<Post>.Filter.AnyEq(x => x.Tags, "mongodb"); 

But how to find a complex item with many fields by a concrete field ? I found the way to write it via the dot notation approach with BsonDocument builder, but how can i do it with typed lambda notations ?

upd

i think it some kind of

builderInst.AnyIn(p => p.ComplexCollection.Select(ml => ml.Id), mlIds) 

but can't check right now, is anyone could help ?

Answer 1

There is ElemMatch

var filter = Builders<Post>.Filter.ElemMatch(x => x.Tags, x => x.Name == "test"); var res = await collection.Find(filter).ToListAsync() 

Answer 2

Here's an example that returns a single complex item from an array (using MongoDB.Driver v2.5.0):

Simple Data Model

public class Zoo {     public List<Animal> Animals { get; set; } }  public class Animal {     public string Name { get; set; } } 

Option 1 (Aggregation)

public Animal FindAnimalInZoo(string animalName) {     var zooWithAnimalFilter = Builders<Zoo>.Filter         .ElemMatch(z => z.Animals, a => a.Name == animalName);      return _db.GetCollection<Zoo>("zoos").Aggregate()         .Match(zooWithAnimalFilter)         .Project<Animal>(             Builders<Zoo>.Projection.Expression<Animal>(z =>                  z.Animals.FirstOrDefault(a => a.Name == animalName)))         .FirstOrDefault(); // or .ToList() to return multiple } 

Option 2 (Filter & Linq) This was about 5x slower for me

public Animal FindAnimalInZoo(string animalName) {     // Same as above     var zooWithAnimalFilter = Builders<Zoo>.Filter         .ElemMatch(z => z.Animals, a => a.Name == animalName);      var zooWithAnimal = _db.GetCollection<Zoo>("zoos")         .Find(zooWithAnimalFilter)         .FirstOrDefault();      return zooWithAnimal.Animals.FirstOrDefault(a => a.Name == animalName); }