How do I use Linq to query nested dynamic BsonDocuments?

问题

public class Foo
{
  public ObjectId _id { get; set; }
  public BsonDocument properties { get; set; }
}

public void FindFoos()
{
  var client = new MongoClient(ConfigurationManager.ConnectionStrings["MongoDB"].ConnectionString);
  var server = client.GetServer();
  var db = server.GetDatabase("FooBar");
  //var collection = db.GetCollection<GeoJsonFeature<GeoJson2DGeographicCoordinates>>("Sections");
  var collection = db.GetCollection<Foo>("Foos");



  collection.Insert(new Foo
  {
    properties = new BsonDocument{
                     {"Foo" , "foo1"},
                     {"Bar" , "bar1"}
                   }
  });
  collection.Insert(new Foo
  {
    properties = new BsonDocument{
                     {"Foo" , "foo2"},
                     {"Bar" , "bar2"}
                   }
  });


  var query = Query<Foo>.Where(foo => foo.properties.AsQueryable().Any(property => property.Name == "Foo" && property.Value.AsString == "foo1"));

  var result = collection.Find(query).First();
}

calling FindFoos results in the following exception:

Unsupported where clause: Queryable.Any(Queryable.AsQueryable(foo.properties), (BsonElement property) => ((property.Name == "Foo") && (property.Value.AsString == "foo1"))).

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentException: Unsupported where clause: Queryable.Any(Queryable.AsQueryable(foo.properties), (BsonElement property) => ((property.Name == "Foo") && (property.Value.AsString == "foo1"))).

at the line:

var query = Query<Foo>.Where(foo => foo.properties.AsQueryable().Any(property => property.Name == "Foo" && property.Value.AsString == "foo1"));

I can do this query easily in the mongodb shell as:

db.Foos.find( {'properties.Foo' : 'foo1'} );

What is the correct way to do this query with Linq?

回答1:

Try LINQ's SelectMany() method. It is used to flatten nested collections. Instead of using nested for loops, we can do the task in a more 'LINQ' way.

Ex given below -

Master m1 = new Master() { name = "A", lstObj = new List<obj> { new obj { i = 1, s = "C++" }, new obj { i = 1, s = "C#" }, new obj { i = 1, s = "Java" } } };

Master m2 = new Master() { name = "A", lstObj = new List<obj> { new obj { i = 4, s = "PHP" }, new obj { i = 5, s = "Ruby" }, new obj { i = 6, s = "Perl" } } };

List<Master> lstMasters = new List<Master> { m1, m2 };
var result = lstMasters.SelectMany(m => m.lstObj).Where(o => o.s == "PHP");

Just replace the Master class with your BsonDocument.

来源：https://stackoverflow.com/questions/21290133/how-do-i-use-linq-to-query-nested-dynamic-bsondocuments

标签

linq

mongodb-.net-driver