MongoDb c# driver find item in array by field value
Solution 1
There is ElemMatch
var filter = Builders<Post>.Filter.ElemMatch(x => x.Tags, x => x.Name == "test");
var res = await collection.Find(filter).ToListAsync()
Solution 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);
}
Solution 3
You need the $elemMatch
operator. You could use Builders<T>.Filter.ElemMatch
or an Any
expression:
Find(x => x.Tags.Any(t => t.Name == "test")).ToListAsync()
http://mongodb.github.io/mongo-csharp-driver/2.0/reference/driver/expressions/#elemmatch
Solution 4
As of the 2.4.2 release of the C# drivers, the IFindFluent interface can be used for querying on array element. ElemMatch cannot be used on an array of strings directly, whereas the find interface will work on either simple or complex types (e.g. 'Tags.Name') and is strongly typed.
FilterDefinitionBuilder<Post> tcBuilder = Builders<Post>.Filter;
FilterDefinition<Post> tcFilter = tcBuilder.Eq("Tags","mongodb") & tcBuilder.Eq("Tags","asp.net");
...
await myCollection.FindAsync(tcFilter);
Linq driver uses the aggregation framework, but for a query with no aggregation operators a find is faster.
Note that this has been broken in previous versions of the driver so the answer was not available at the time of original posting.
Vladyslav Furdak
Updated on March 17, 2020Comments
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Vladyslav Furdak about 4 years
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 ?
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shiva8 over 7 yearsThis is not an optimal solution. The best solution is to use api.mongodb.com/csharp/current/html/…
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rnofenko over 7 years@shiva8 You can not user
AnyIn
when you have array of complex objects. -
LMK over 5 yearsWarning, Any() doesn't work when targeting Azure CosmosDB - see feedback.azure.com/forums/263030-azure-cosmos-db/suggestions/…
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Surya Deepak over 5 yearsHello Aaron, your solution had fixed my problem.However, i would like to know the performance of this, if there are close to a lakh records.
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Geraldo Neto about 4 yearsAny idea on why the second option is (about 5x) slower than the first one?