String case sensitive in LiteDB query

I have questioned at stackoverflow https://stackoverflow.com/q/44184505/1011174 1 mouth ago

In various environment, the user name is case insensitive. We query admin equal to ADMIN. I have searched LiteDB called CompareTo to compare two objects that I can’t find a point to make string compared as case insensitive.

The code in QueryEquals.cs

internal override IEnumerable<IndexNode> ExecuteIndex(IndexService indexer, CollectionIndex index)
{
    var node = indexer.Find(index, _value, false, Query.Ascending);

    if (node == null) yield break;

    yield return node;

    if (index.Unique == false)
    {
        // navigate using next[0] do next node - if equals, returns
        while (!node.Next[0].IsEmpty && ((node = indexer.GetNode(node.Next[0])).Key.CompareTo(_value) == 0))
        {
            if (node.IsHeadTail(index)) yield break;

            yield return node;
        }
    }
}

The propositional we can case insensitive

using (var db = new LiteRepository("lite.db"))
{
    db.Insert(new User { Name = "John" });
    var user = db.Query<User>()
        .Where(x => x.Name == "JOHN")
        .FirstOrDefault(); // proposal return John
    var fail = db.Query<User>()
        .Where(x => string.Equals(x.Name, "JOHN", StringComparison.OrdinalIgnoreCase))
        .FirstOrDefault(); // throw exception
}

Another consideration, it is a possible to execute lambda expression in LiteDB without conversion by visitor?

[mbdavid]

Done in v4 beta! Now you can write expression functions in index definition.

col.EnsureIndex(x => x.Name, false, "LOWER($.Name)")

After you can search using lower case.

[mbdavid]

Hi @trichling, after read this I’m thiking in create “index function transformation” that can by applied on index before store. Some basics function could be “lower”, “upper”, “toInt”, “trim” that can be easy to implement. Using this kind of definition on index (not on field) I can apply for all documents, including exist documents.

I will think better and write a propose about this.