dagger/dagger · error · InvalidQueryError

No field has been selected

Error message

No field has been selected

What it means

The Python Dagger client builds GraphQL queries incrementally by appending selections to a context. Query.build() refuses to serialize a query with zero selections, raising InvalidQueryError("No field has been selected"), because a selection set with no fields is not a valid GraphQL request.

Source

Thrown at sdk/python/src/dagger/client/_core.py:165

        return ctx.select("Query", field_name, args)

    def select_id(self, type_name: str, id_value: str) -> "Context":
        """Load an object by its ID via node(id:) with an inline fragment."""
        ctx = dataclasses.replace(self, selections=collections.deque())
        node_field = Field(
            type_name="Query",
            name="node",
            args={"id": id_value},
            inline_type=type_name,
        )
        selections = ctx.selections.copy()
        selections.append(node_field)
        return dataclasses.replace(ctx, selections=selections)

    async def build(self) -> DSLSelectable:
        if not self.selections:
            msg = "No field has been selected"
            raise InvalidQueryError(msg)

        def _collapse(child: Field, field_: Field):
            return field_.add_child(child)

        # This transforms the selection set into a single root Field, where
        # the `children` attribute is set to the next selection in the set,
        # and so on...
        root = functools.reduce(_collapse, reversed(self.selections))

        # `to_dsl` will cascade to all children, until the end.
        try:
            return root.to_dsl(DSLSchema(await self.conn.session.get_schema()))
        except (graphql.GraphQLError, AttributeError, TypeError) as e:
            logger.exception("GraphQL query builder failed to build query")
            msg = (
                "Failed to build GraphQL query, probably due to a schema validation "
                "issue. Please file a bug report because anything that could "
                "fail to validate at this point should really happen sooner. "

View on GitHub (pinned to 82ba2681db)

Solutions

1. Ensure at least one field is selected before executing, e.g. `await client.query().version` or `.container().id()`
2. If fields are conditional, guarantee a default field or raise earlier when none apply
3. Check you're awaiting the final field object, not the intermediate query builder
4. For dynamic code, assert the selections were added before execute

Example fix

# before
q = client.query()
if include_version:
    q = q.select("version")
result = await q.execute()  # InvalidQueryError when include_version is False
# after
q = client.query().select("version")  # always select a base field
result = await q.execute()

def is_executable(q) -> bool:
    return bool(getattr(q, '_ctx', None) and getattr(q._ctx, 'selections', None))

if not is_executable(client.query()):
    raise RuntimeError('query has no fields selected')

def has_selections(q) -> bool:
    ctx = getattr(q, '_ctx', None)
    return bool(ctx and getattr(ctx, 'selections', None))

try:
    result = await q.execute()
except dagger.InvalidQueryError:
    raise RuntimeError('no field selected on query; call at least one field before execute')

When it happens

Trigger: Calling `await`/`execute` (which triggers build via request) on a client/query object that never had a field selected — e.g. `client.query().execute()`, awaiting an empty sub-selection, or constructing a Client/Root manually without `.some_field()` calls.

Common situations: Dynamically building queries with conditional field calls where every branch was skipped, chaining mistakes like `client.query()` assigned but fields appended to a different object, or awaiting an intermediate object instead of the final field.

Related errors

• Errors list is empty
• Failed to build GraphQL query, probably due to a schema vali
• Failed to build schema from introspection query: {msg}
• No schema in session
• merge module types into schema: %w

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/1dd61cc34d606d31. Report an issue: GitHub.