MongoDB C# Query Array of Objects that contain a property value

Question

My documents have an array property in them. Lets call it arrayProperty something like this:

 {
  _id: mongoObjectIdThingy,
  arrayProperty: [
    {string1: "aString",otherProperty:"somethingelse"},
    {string1: "aString2",otherProperty:"somethingelse"}
  ]
}

I'm using the mongodb c# driver. I want to find all documents that contain any of a list of string1 values. For example say I have a list of strings:

["a","b","aString"]

I want the query to return the above document. I've tried this:

    var builder = Builders<MyObject>.Filter;

    var listToFind = new List<string>{"a","b","aString"};


    return builder.ElemMatch(o => o.arrayProperty,
        d => listToFind.Contains(d.string1));

But got this exception:

Unsupported filter: Contains(value(System.Collections.Generic.List`1[System.String]))

It seems like I can't do a contains linq expression in the driver's filter expression. How does one write this type of query in mongoDB with C#?

it works to me, which version are you using?

owairc
– owairc

2020-02-17 21:26:17 +00:00
Commented Feb 17, 2020 at 21:26 — owairc
– owairc, Commented Feb 17, 2020 at 21:26

Skami · Accepted Answer · 2020-02-17 22:19:49Z

5

I believe you are looking for the In FilterDefinition, which would make your Builder look like this;

return Builders<MyObject>.Filter.ElemMatch(
            o => o.arrayProperty,
            Builders<ArrayProperty>.Filter.In(y => y.string1, listToFind));

This builds this query

db.MyObject.find({ "arrayProperty" : { "$elemMatch" : { "string1" : { "$in" : ["a", "b", "aString"] } } } })

To be able to use the Regex you would have to build a different query (I'm not on coffee so this is without any warranty)

        var listToFind = new List<string> { "a", "b", "astring" };

        var regexList = listToFind.Select(x => new BsonRegularExpression(x, "i"));

        var filterList = new List<FilterDefinition<MyObject>>();
        foreach (var bsonRegularExpression in regexList)
        {
            FilterDefinition<MyObject> fil = Builders<MyObject>.Filter.ElemMatch(o => o.arrayProperty, Builders<ArrayProperty>.Filter.Regex(
                 x => x.string1,
                 bsonRegularExpression));

            filterList.Add(fil);
        }


        var orFilter = Builders<MyObject>.Filter.Or(filterList);

        var result = collection.Find(orFilter).ToList();

Which builds the follow query

db.MyObject.find({ "$or" : [{ "arrayProperty" : { "$elemMatch" : { "string1" : /a/i } } }, { "arrayProperty" : { "$elemMatch" : { "string1" : /b/i } } }, { "arrayProperty" : { "$elemMatch" : { "string1" : /astring/i } } }] })

edited Feb 17, 2020 at 22:19

answered Feb 17, 2020 at 21:19

Skami

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7 Comments

cobolstinks Over a year ago

Where is the In Filter definition used in your answer?

Skami Over a year ago

Good point, I wrote the wrong part here. Updated now. @cobolstinks

cobolstinks Over a year ago

hmm having difficulty implementing this. Is Builders<ArrayProperty> the type of my object array? or is that some MongoDB driver built in class?

Skami Over a year ago

It's the class I assumed your model had for the arrayProperty array. Could your post your models? To answer your question, yes it's the type of your object array.

cobolstinks Over a year ago

ok cool that worked thanks! However one last wrinkle is i want the search to be case insensitive. Is there a flag to pass in the In clause for this?

|

Thilina Koggalage · Accepted Answer · 2021-06-09 18:28:59Z

1

Another workaround is using "Any" instead of "Contain".

return builder.ElemMatch(o => o.arrayProperty,
        d => listToFind.Any(y => y == d.string1));

answered Jun 9, 2021 at 18:28

Thilina Koggalage

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