MongoDB linq C# select document where array of subdocumnets contain all values from string array

Question

I have a collection on MongoDb with a similar stricture to the object below.

{
    _id: ObjectId("0000000"),
    groupName: "Group A",
    users[
        {
            userId: "1111111",
            rollDescription: "Some Text Here"
        },
        {
            userId: "2222222",
            rollDescription: "Some Text Here"
        },
        {
            userId: "3333333",
            rollDescription: "Some Text Here"
        }
    ]
}

Elsewhere in the system an array of "userIds" is generated and I need to select all groups that contain all userIds in the array.

Is it possible to do this using just linq?

I know I can use this if I had just an array of userIds:

from g in groups.AsQueryable<Group>() where g.Users.ContainsAll(usersIds.ToArray()) select g;

Is there something similar for querying an array of subdocumnets instead of an array of strings?

Jason Fry · Accepted Answer · 2014-10-07 02:39:18Z

1

Here's how I'd do it in a MongoDB query:

db.collection.find({ "users.userId": { $all: [ "1111111", "2222222", "3333333" ] }})

I think LINQ will be quite a bit trickier. Does this work (I don't have MongoDB installed)?

from g in groups.AsQueryable<Group>() where g.Users.ConvertAll(u => g.UserId).AsQueryable().ContainsAll(userIds) select g;

Even if it did I suspect that it will not be as performant as using the MongoDB query builder:

groups.Find(Query.All("users.userId", userIds))

answered Oct 7, 2014 at 2:39

Jason Fry

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2 Comments

Paul Over a year ago

The LINQ compiles with the following change"ConvertAll(u => u.UserId)" but on runtime I get the error: Unable to determine the serialization information for the expression: Queryable.AsQueryable<String>(g.Users.ConvertAll<String>((User u)=> u.UserId)). I have been unable to solve the error so far. The solution using groups.Find is working. I just had to make the following change "groups.Find(Query.All("users.userId", new BsonArray(userIds)))"

Paul Over a year ago

It would still be nice to get this fully working with LINQ since the system is in development, and it avoids people renaming things and breaking the query, but for now the Mongo query works.

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