how to make a mongo filter search case insensitive in c#

I have this query here:

            var filter =
        builder.Eq("BuyerDetails.Buyer.Email", request.BuyerEmail)
                 | builder.Eq("BuyerDetails.Buyer.FirstName", request.FirstName)
                 & builder.Eq("BuyerDetails.Buyer.Surname", request.LastName);

however the problem is that i am unable anticipate the case of the email, firstname and surname is mongo.

if the request is firstName = "STACK" and LastName = "OVERFLOW"

and the document in mongo is "firstName = "stack" and LastName = "overflow"

it will not match.

how can i filter with and make it case insensitive?

>Solution :

You need to work with the $regex operator. In MongoDB .NET Driver, refer to FilterDefinitionBuilder.Regex Method (FieldDefinition, BsonRegularExpression).

using System.Text.RegularExpressions;

builder.Regex("BuyerDetails.Buyer.FirstName", new Regex(request.FirstName, RegexOptions.IgnoreCase))

builder.Regex("BuyerDetails.Buyer.Surname", new Regex(request.LastName, RegexOptions.IgnoreCase))

Note that the above query will find the document with the field value without guarantee from start to end. Example of illustration:

Search keyword for FirstName: Stack

If you want to filter the document with the match of the filtered string from start to end (exact match), you need the ^ start and $ end symbols in regex.

var filter =
    builder.Eq("BuyerDetails.Buyer.Email", request.BuyerEmail)
    | builder.Regex("BuyerDetails.Buyer.FirstName", new Regex($"^{request.FirstName}$", RegexOptions.IgnoreCase))
    & builder.Regex("BuyerDetails.Buyer.Surname", new Regex($"^{request.LastName}$", RegexOptions.IgnoreCase));