How to find an element in nested child array document in MongoDB using c#

Question

I have below document, I am trying to search an element which is inside the nested document "ids",

If element is found return value bool or count. I tried with Mongodb query but not sure how to write a query for an array elements. error :-Operator == cannot be applied to operands of type 'string[]' and 'string'

foreach (var req in _addUpdateRailsObjectInfoRequest.ids)
{
      string value=req.id

  var isIdExists = Builders<RailsData>.Filter.And(
  Builders<RailsData>.Filter.ElemMatch(c => c.content.queryInclude, c => c.type == req.type),
  Builders<RailsData>.Filter.ElemMatch(c => c.content.queryInclude, c => c.ids == value));
 }

//Error at last line near c.id==value. Operator == cannot be applied to operands of type 'string[]' and 'string'

 {
        "_id" : ObjectId("5c2d3e700aff6771ebfc88ea"),
        "name" : "Toyota",
            "content" : {
            "queryInclude" : [ 
                {
                    "type" : "departments",
                    "ids" : [ 
                        "21", 
                        "18", 
                        "19", 
                        "29", 
                        "30"
                    ]
                }
            ]
        }
    }

//

public class RailsData
{
    public string name { get; set; }
    public content content { get; set; }
}

 public class content
 {
   public List<queryInclude> queryInclude { get; set; }
 }

    public class queryInclude
    {
        public string type { get; set; } 
        public string[] ids { get; set; }
    }

How about this one: Builders<RailsData>.Filter.ElemMatch(c => c.content.queryInclude, c => c.ids.Contains(value));? — Tetsuya Yamamoto
– Tetsuya Yamamoto, Commented Jan 3, 2019 at 4:58

Tetsuya Yamamoto · Accepted Answer · 2019-01-03 05:52:30Z

3

The exception message is self-explanatory: you cannot use equality comparison operator (==) between a string and string[] array, because they have different types. According to ElemMatch documentation, you can use Any() extension method:

Builders<RailsData>.Filter.ElemMatch(c => c.content.queryInclude, c => c.ids.Any(x => x == value));

Or use Contains() as alternative:

Builders<RailsData>.Filter.ElemMatch(c => c.content.queryInclude, c => c.ids.Contains(value));

answered Jan 3, 2019 at 5:52

Tetsuya Yamamoto

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1 Comment

Shakeer Hussain Over a year ago

Thanks for your reply, There is no error after using Contains. But how to return a value if element is found?

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