Dapper template doesn't work with collection parameters

[skolima]

I might be hitting a bug in Dapper, as I haven't found a nice way to resolve this.

I've got an ID type:

[StronglyTypedId(Template.Guid, "guid-dapper")]
public readonly partial struct MyId { }

and register the generated TypeHandler:

SqlMapper.AddTypeHandler(new MyId.DapperTypeHandler());

but when running a Dapper SQL query that uses a collection type parameter, not a singular parameter - let's say with criteria

"WHERE entity_id = ANY(@entityIds)"

Dapper (with Npgsql data access) throws the following exception:

System.InvalidCastException

Writing values of '<>z__ReadOnlySingleElementList`1[[Domain.Types.MyId]]' is not supported for parameters having no NpgsqlDbType or DataTypeName. Try setting one of these values to the expected database type..
   at Npgsql.Internal.AdoSerializerHelpers.<GetTypeInfoForWriting>g__ThrowWritingNotSupported|1_0(Type type, PgSerializerOptions options, Nullable`1 pgTypeId, Nullable`1 npgsqlDbType, Exception inner)
   at Npgsql.Internal.AdoSerializerHelpers.GetTypeInfoForWriting(Type type, Nullable`1 pgTypeId, PgSerializerOptions options, Nullable`1 npgsqlDbType)
   at Npgsql.NpgsqlParameter.ResolveTypeInfo(PgSerializerOptions options)
   at Npgsql.NpgsqlParameterCollection.ProcessParameters(PgSerializerOptions options, Boolean validateValues, CommandType commandType)
   at Npgsql.NpgsqlCommand.ExecuteReader(Boolean async, CommandBehavior behavior, CancellationToken cancellationToken)
   at Npgsql.NpgsqlCommand.ExecuteReader(Boolean async, CommandBehavior behavior, CancellationToken cancellationToken)
   at Npgsql.NpgsqlCommand.ExecuteDbDataReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken)
   at Dapper.SqlMapper.QueryAsync[T](IDbConnection cnn, Type effectiveType, CommandDefinition command) in /_/Dapper/SqlMapper.Async.cs:line 434

(this particular parameter was [new MyId(value)]) but it fails same way for every collection type.

A workaround I'm using currently is instead passing the collection parameters in as

entityIds = ids.Select(i=>i.value).ToArray()

I was looking how the dapper template would need to be extended to cater for collection parameters but failed to get it to work.

[andrewlock]

<>z__ReadOnlySingleElementList1[[Domain.Types.MyId]]` is characteristic of a collection generated by collection-expressions 🤔 I wonder if the problem is purely Dapper's support for the collection type...

For example, what happens if you explicitly define entityIds as an MyId[]?

I don't think this points to an issue in StronglyTypedId, but I'm not 100% 🤔