def check_models_have(models, key):
    """Check models have deserialized the provided key."""
    n_err_models = 0
    for m in models:
        if not m.is_deserialized(key):
            n_err_models += 1
    if n_err_models:
        return "errors: {}/{} models {} don't have key {}".format(
            n_err_models, len(models), models[0].__class__.__name__, key
        )