MongoDB C# driver, query by an array element using regex

Question

I am using MongoDB C# driver version 2.2. My collection contains "Parent" objects. Each parent object has an array of children objects. Each child has name value:

"parent": {
    "children":[
        { "name": "Bob", "age": 10},
        { "name": "Alice", "age": 7},
        { "name": "Tobias", "age": 11}
    ]
}

I need to translate the following code into C# statements / LINQ syntax:

db.getCollection('Parents').find({'parent.children': { $elemMatch: { 'name': { $regex: '.*ob.*', $options: 'im' } }}})

I have found there are methods like

var builder = Builders<BsonDocument>.Filter;
builder.Regex("parent.children.name", new BsonRegularExpression(".*ob.*")); //does not work with array

and

builder.AnyEq("parent.children.name", "ob"); //without regex

But I cannot understand how to combine them. Please advise.

UPDATE:

I am using the following for now, please correct me if you know a reason why it should not work correctly:

builder.AnyEq("parent.children.name", new BsonRegularExpression(".*ob.*"))

Your final query looks fine to me, btw!

Nick Bull
– Nick Bull

2016-08-01 13:17:34 +00:00
Commented Aug 1, 2016 at 13:17 — Nick Bull
– Nick Bull, Commented Aug 1, 2016 at 13:17

Antipod · Accepted Answer · 2016-08-07 15:24:22Z

2

I am using the following for now:

builder.AnyEq("parent.children.name", new BsonRegularExpression(".*ob.*"))

answered Aug 7, 2016 at 15:24

Antipod

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Nick Bull · Accepted Answer · 2016-08-01 13:03:47Z

1

Can't test C# on this machine. Let me know if this doesn't work:

var filter = Builders<People>.Filter.ElemMatch(x => x.Parent.Children, x => Regex.IsMatch(x.Name, "regex"));
var res = await collection.Find(filter).ToListAsync();

Here's a trick you might like btw:

// Take your inputted `find` query string:
string bsonQuery = "{'parent.children': { $elemMatch: { 'name': { $regex: '.*ob.*', $options: 'im' } }}}";

// Use it as the filter!
var filter = MongoDB.Bson.Serialization.BsonSerializer.Deserialize<BsonDocument>(bsonQuery);

// Results:
var result = col.FindSync (filter).ToList();

edited Aug 1, 2016 at 13:03

answered Aug 1, 2016 at 12:53

Nick Bull

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5 Comments

Antipod Over a year ago

In your example you use classes (strongly-typed). All I have is a dotted notation of the "path". Can you please improve your example?

Nick Bull Over a year ago

@Antipod Look up COPOs. They'll make your life a lot easier when querying using C#

Antipod Over a year ago

Thank you for the update. I am almost sure the provided update will work. The issue is: it is a string and I do not want to construct strings, we have the methods in the driver which we can use and the driver will construct queries for us, after all: ) Speaking about POCOs, I 100% agree with you, but I have a requirement - JSON does not have a defined structure, it is dynamic.

Nick Bull Over a year ago

Whilst JSON is dynamic, your first-class objects in C# are not. So writing COPOs on a use-by-use basis even if the data may change makes sense for the C# code operating on them.

Antipod Over a year ago

thank you for your opinion. Unfortunately, POCO is an off-topic in my question, sorry for that :) BTW, I have updated the question.

nablag · Accepted Answer · 2020-11-13 18:34:38Z

I've tested your current expression (builder.AnyEq("parent.children.name", new BsonRegularExpression(".*ob.*")) on a database at home and I don't believe it behaves in the way you intend.

Although the c# documentation doesn't explicitly state this, mongoDB supports the Regex filter on an array field. I have tested the below expression in C# and have correct results for the Regex despite the field being an array.

builder.Regex(MONGO_FIELD_NAME, new BsonRegularExpression("SOME REGEX"));

In addition, I've tested Regex on the toy example in the [online mongo webshell for query arrays] (https://docs.mongodb.com/manual/tutorial/query-arrays/). Querying for db.inventory.find({tags : {$regex : "^bl"}} will return results with "blank" or "blue" despite the "tag" field being an array.

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