litedb-org/LiteDB · error · NotSupportedException

Constructor for are not supported when convert to…

Error message

Constructor for {node.Type.Name} are not supported when convert to BsonExpression ({node.ToString()}).

What it means

Thrown by VisitNew when a new SomeType(args) expression is encountered, SomeType has a registered ITypeResolver, but ResolveCtor returns null for the constructor used. The type is recognized by the resolver system, but the specific constructor overload has no translation pattern.

Solutions

Use a supported constructor overload for the type (check the resolver source for recognized ctors).
Hoist the value into a closure variable so the visitor evaluates it in memory instead of translating the constructor.
Use a raw BsonExpression or a pre-computed constant.

Example fix

// before
col.Find(x => x.CreatedAt > new DateTime(2020, 1, 1, 0, 0, 0, DateTimeKind.Utc));
// unsupported DateTime ctor overload

// after -- hoist the constant
var cutoff = new DateTime(2020, 1, 1, 0, 0, 0, DateTimeKind.Utc);
col.Find(x => x.CreatedAt > cutoff);

Defensive patterns

Strategy: validation

Validate before calling

// Hoist new SomeType(args) into a closure variable so it is evaluated in memory
var cutoff = new DateTime(2020, 1, 1, 0, 0, 0, DateTimeKind.Utc); // evaluate outside
col.Find(x => x.CreatedAt > cutoff);

Try / catch

try
{
    var results = col.Find(x => x.CreatedAt > new DateTime(2020, 1, 1, 0, 0, 0, DateTimeKind.Utc));
}
catch (NotSupportedException ex) when (ex.Message.Contains("Constructor for"))
{
    var cutoff = new DateTime(2020, 1, 1, 0, 0, 0, DateTimeKind.Utc);
    results = col.Find(x => x.CreatedAt > cutoff);
}

Prevention

Avoid constructing resolver-backed types (DateTime, Guid, etc.) inline in LINQ queries; hoist them into closure variables.
Use the simplest constructor overload if inline construction is unavoidable.
Write unit tests for each predicate to catch unsupported constructors early.

When it happens

Trigger: Using new with a resolver-backed type and a constructor the resolver does not support. For example new DateTime(2020, 1, 1, 12, 0, 0, DateTimeKind.Utc) if DateTimeResolver does not have a pattern for that 6-argument overload, or new Guid(byteArray) if GuidResolver lacks that ctor.

Common situations: Using an uncommon constructor overload of a built-in type in a LINQ query predicate or projection. Passing calendar/timezone arguments that the resolver does not map.

Related errors

AI-assisted analysis of litedb-org/LiteDB@f906a5f850 (2026-08-13). Data as JSON: /api/errors/dd2a81dfd54205ff. Report an issue: GitHub.

Appendix: source

Thrown at LiteDB/Client/Mapper/Linq/LinqExpressionVisitor.cs:360

            {
                base.VisitUnary(node);
            }

            return node;
        }

        /// <summary>
        /// Visit :: x => `new { x.Id, x.Name }`
        /// </summary>
        protected override Expression VisitNew(NewExpression node)
        {
            if (node.Members == null)
            {
                if (TryGetResolver(node.Type, out var type))
                {
                    var pattern = type.ResolveCtor(node.Constructor);

                    if (pattern == null) throw new NotSupportedException($"Constructor for {node.Type.Name} are not supported when convert to BsonExpression ({node.ToString()}).");

                    this.ResolvePattern(pattern, null, node.Arguments);
                }
                else
                {
                    throw new NotSupportedException($"New instance are not supported for {node.Type} when convert to BsonExpression ({node.ToString()}).");
                }
            }
            else
            {
                _builder.Append("{ ");

                for (var i = 0; i < node.Members.Count; i++)
                {
                    var member = node.Members[i];
                    _builder.Append(i > 0 ? ", " : "");
                    _builder.AppendFormat("'{0}': ", member.Name);
                    this.Visit(node.Arguments[i]);

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