When a model won’t load · onemodel cookbook

What OneModel reports when an ONNX model uses an operator it doesn’t implement, or one without an exact kernel in exact mode, and how to read the error.

Two small models, made with the onnx Python package: unsupported.onnx uses DeformConv and TfIdfVectorizer, which the 0.3.0 preview doesn’t implement, and wave.onnx uses Cos, which has a fast kernel but no exact one. broken_models.py:

PYTHON

import numpy as np, onnx
from onnx import helper as h, TensorProto as T, numpy_helper as nh
# unsupported.onnx: two operators the 0.3.0 preview has no kernel for
g = h.make_graph(
    [h.make_node("DeformConv", ["x", "w", "offset"], ["y"]),
     h.make_node("TfIdfVectorizer", ["ids"], ["tfidf"], mode="TF", min_gram_length=1, max_gram_length=1,
                 max_skip_count=0, ngram_counts=[0], ngram_indexes=[0], pool_int64s=[1])],
    "unsupported",
    [h.make_tensor_value_info("x", T.FLOAT, [1, 1, 3, 3]), h.make_tensor_value_info("w", T.FLOAT, [1, 1, 2, 2]),
     h.make_tensor_value_info("offset", T.FLOAT, [1, 8, 2, 2]), h.make_tensor_value_info("ids", T.INT64, [4])],
    [h.make_tensor_value_info("y", T.FLOAT, None), h.make_tensor_value_info("tfidf", T.FLOAT, None)])
onnx.save(h.make_model(g, opset_imports=[h.make_opsetid("", 22)], ir_version=10), "unsupported.onnx")
# wave.onnx: Cos has a fast kernel but no exact one in 0.3.0
g = h.make_graph([h.make_node("Cos", ["t"], ["y"])], "wave",
    [h.make_tensor_value_info("t", T.FLOAT, [4])], [h.make_tensor_value_info("y", T.FLOAT, [4])])
onnx.save(h.make_model(g, opset_imports=[h.make_opsetid("", 17)], ir_version=8), "wave.onnx")
print("ok")

using RecursiveAI.OneModel;
using RecursiveAI.OneModel.Graph;
 
try
{
    Model.Load("unsupported.onnx");
}
catch (SessionException e)
{
    Console.WriteLine($"{e.Kind}: {e.Message}");
    foreach (string op in e.Operators) Console.WriteLine($"  missing: {op}");
}
 
try
{
    Model.Load("wave.onnx", new SessionOptions { Mode = ExecutionMode.Exact });
}
catch (SessionException e)
{
    Console.WriteLine($"{e.Kind}: {e.Message}");
}
 
using var fast = Model.Load("wave.onnx");   // the same model runs in fast mode
Console.WriteLine(string.Join(", ", fast.Run([0f, 1f, 2f, 3f]).Select(x => x.ToString("F6"))));

Text

UnsupportedOperator: The model uses operators this library does not implement: DeformConv (opset 22), TfIdfVectorizer (opset 22).
  missing: DeformConv (opset 22)
  missing: TfIdfVectorizer (opset 22)
ExactModeUnavailable: Exact mode is not available: no exact kernel exists for Cos. Use ExecutionMode.Fast or remove these operators.
1.000000, 0.540302, -0.416147, -0.989992

Reading the error

SessionException.Kind is UnsupportedOperator or ExactModeUnavailable; Operators lists every operator involved, each with its opset, so one load tells you everything a model needs.
The check happens in Model.Load, before any input is read. Nothing half-runs.
Other kinds: InvalidModel (the graph is malformed, with the node name), InvalidInput (a wrong name, type or shape at Run), Unsupported and Disposed. A file that isn’t valid ONNX at all is an OnnxImportException.

Which operators pass the ONNX backend tests, in fast and in exact mode, and the reason for every gap, is in conformance.