Same as an ExprBuilder but contains the shape of the resulting query.
The result is a document that maps the field Name to the resulting values
from applying the Expr associated with that name.
NB: The shape is more restrictive than $project because we may need to
convert it to a GroupBuilder, and a nested Reshape can be realized
with a chain of DocBuilders, leaving the collapsing to
Workflow.coalesce.
Same as an
ExprBuilderbut contains the shape of the resulting query. The result is a document that maps the field Name to the resulting values from applying theExprassociated with that name. NB: The shape is more restrictive than $project because we may need to convert it to aGroupBuilder, and a nestedReshapecan be realized with a chain of DocBuilders, leaving the collapsing to Workflow.coalesce.