How to use the resolwe.process.fields.ValidationError function in resolwe

size = value.get("size", None)
            if size is not None and not isinstance(size, int):
                raise ValidationError("field's size element must be an integer")

            total_size = value.get("total_size", None)
            if total_size is not None and not isinstance(total_size, int):
                raise ValidationError("field's total_size element must be an integer")

            refs = value.get("refs", None)
            if refs is not None and not isinstance(refs, list):
                # TODO: Validate that all refs are strings.
                raise ValidationError("field's refs element must be a list of strings")

            return DirDescriptor(path, size=size, total_size=total_size, refs=refs,)
        elif not isinstance(value, None):
            raise ValidationError("field must be a DirDescriptor, string or a dict")

def to_python(self, value):
        """Convert value if needed."""
        if value is not None:
            try:
                return int(value)
            except (TypeError, ValueError):
                raise ValidationError("field must be an integer")

def to_python(self, value):
        """Convert value if needed."""
        if value is not None:
            try:
                return float(value)
            except (TypeError, ValueError):
                raise ValidationError("field must be a float")

def to_python(self, value):
        """Convert value if needed."""
        if isinstance(value, FileDescriptor):
            return value
        elif isinstance(value, str):
            return FileDescriptor(value)
        elif isinstance(value, dict):
            try:
                path = value["file"]
            except KeyError:
                raise ValidationError("dictionary must contain a 'file' element")

            if not isinstance(path, str):
                raise ValidationError("field's file element must be a string")

            size = value.get("size", None)
            if size is not None and not isinstance(size, int):
                raise ValidationError("field's size element must be an integer")

            total_size = value.get("total_size", None)
            if total_size is not None and not isinstance(total_size, int):
                raise ValidationError("field's total_size element must be an integer")

            is_remote = value.get("is_remote", None)
            if is_remote is not None and not isinstance(is_remote, bool):
                raise ValidationError("field's is_remote element must be a boolean")

            file_temp = value.get("file_temp", None)
            if file_temp is not None and not isinstance(file_temp, str):
                raise ValidationError("field's file_temp element must be a string")

elif isinstance(value, dict):
            try:
                path = value["dir"]
            except KeyError:
                raise ValidationError("dictionary must contain a 'dir' element")

            if not isinstance(path, str):
                raise ValidationError("field's dir element must be a string")

            size = value.get("size", None)
            if size is not None and not isinstance(size, int):
                raise ValidationError("field's size element must be an integer")

            total_size = value.get("total_size", None)
            if total_size is not None and not isinstance(total_size, int):
                raise ValidationError("field's total_size element must be an integer")

            refs = value.get("refs", None)
            if refs is not None and not isinstance(refs, list):
                # TODO: Validate that all refs are strings.
                raise ValidationError("field's refs element must be a list of strings")

            return DirDescriptor(path, size=size, total_size=total_size, refs=refs,)
        elif not isinstance(value, None):
            raise ValidationError("field must be a DirDescriptor, string or a dict")

def clean(self, value):
        """Run validators and return the clean value."""
        if value is None:
            value = self.default

        try:
            value = self.to_python(value)
            self.validate(value)
        except ValidationError as error:
            raise ValidationError(
                "invalid value for {}: {}".format(self.name, error.args[0])
            )
        return value

def validate(self, value):
        """Validate field value."""
        if value is not None and not isinstance(value, bool):
            raise ValidationError("field must be a boolean")

        super().validate(value)

def validate(self, value):
        """Validate field value."""
        if self.required and value is None:
            raise ValidationError("field is required")

        if value is not None and self.choices is not None:
            choices = [choice for choice, _ in self.choices]
            if value not in choices and not self.allow_custom_choice:
                raise ValidationError(
                    "field must be one of: {}".format(", ".join(choices),)
                )

def to_python(self, value):
        """Convert value if needed."""
        if isinstance(value, str):
            return value
        elif isinstance(value, dict):
            try:
                value = value["url"]
            except KeyError:
                raise ValidationError("dictionary must contain an 'url' element")

            if not isinstance(value, str):
                raise ValidationError("field's url element must be a string")

            return value
        elif not isinstance(value, None):
            raise ValidationError("field must be a string or a dict")

size = value.get("size", None)
            if size is not None and not isinstance(size, int):
                raise ValidationError("field's size element must be an integer")

            total_size = value.get("total_size", None)
            if total_size is not None and not isinstance(total_size, int):
                raise ValidationError("field's total_size element must be an integer")

            is_remote = value.get("is_remote", None)
            if is_remote is not None and not isinstance(is_remote, bool):
                raise ValidationError("field's is_remote element must be a boolean")

            file_temp = value.get("file_temp", None)
            if file_temp is not None and not isinstance(file_temp, str):
                raise ValidationError("field's file_temp element must be a string")

            refs = value.get("refs", None)
            if refs is not None and not isinstance(refs, list):
                # TODO: Validate that all refs are strings.
                raise ValidationError("field's refs element must be a list of strings")

            return FileDescriptor(
                path,
                size=size,
                total_size=total_size,
                is_remote=is_remote,
                file_temp=file_temp,
                refs=refs,
            )
        elif not isinstance(value, None):
            raise ValidationError("field must be a FileDescriptor, string or a dict")