DYNDB106: Unsupported collection type

Field	Value
Code	DYNDB106
Severity	Error

Message

Property '{0}' has unsupported collection type '{1}'; use Dictionary<string, T>, HashSet<T>, or List<T> instead

Description

Only specific collection types are supported for DynamoDB mapping. The source generator supports List<T> (mapped to L), HashSet<T> (mapped to SS/NS/BS), and Dictionary<string, T> (mapped to M). Other collection types cannot be automatically mapped.

Example

The following code triggers this diagnostic:

[DynamoDbTable("Users")]
public partial class User
{
    [PartitionKey]
    [DynamoDbAttribute("pk")]
    public string Pk { get; set; } = string.Empty;

    [DynamoDbAttribute("roles")]
    public LinkedList<string> Roles { get; set; } = new();
}

Fix

The corrected version:

[DynamoDbTable("Users")]
public partial class User
{
    [PartitionKey]
    [DynamoDbAttribute("pk")]
    public string Pk { get; set; } = string.Empty;

    [DynamoDbAttribute("roles")]
    public HashSet<string> Roles { get; set; } = new();
}