metabase.query-processor.middleware.add-dimension-projections
Middleware for adding remapping and other dimension related projections. This remaps Fields that have a corresponding
Dimension object (which defines a remapping) in two different ways, depending on the :type attribute of the
Dimension:
external type Dimensions mean the Field's values will be replaced with corresponding values from a column on a
different table, joined via a foreign key. A common use-case would be to replace FK IDs with the name of whatever it
references, for example replacing a values of venue.category_id with values of category.name. Actual replacement
of values happens on the frontend, so this middleware simply adds the column to be used for replacement (e.g.
category.name) to the :fields clause in pre-processing, so the Field will be fetched. Recall that Fields
referenced via with :fk-> clauses imply that JOINs will take place, which are automatically handled later in the
Query Processor pipeline. Additionally, this middleware will swap out and :order-by clauses referencing the
original Field with ones referencing the remapped Field (for example, so we would sort by category.name instead of
category_id).
internal type Dimensions mean the Field's values are replaced by a user-defined map of values, stored in the
human_readable_values column of a corresponding FieldValues object. A common use-case for this scenario would be
to replace integer enum values with something more descriptive, for example replacing values of an enum can_type
-- 0 becomes Toucan, 1 becomes Pelican, and so forth. This is handled exclusively in post-processing by
adding extra columns and values to the results.
In both cases, to accomplish values replacement on the frontend, the post-processing part of this middleware adds
appropriate :remapped_from and :remapped_to attributes in the result :cols in post-processing.
:remapped_from and :remapped_to are the names of the columns, e.g. category_id is :remapped_to name, and
name is :remapped_from :category_id.
Middleware for adding remapping and other dimension related projections. This remaps Fields that have a corresponding Dimension object (which defines a remapping) in two different ways, depending on the `:type` attribute of the Dimension: `external` type Dimensions mean the Field's values will be replaced with corresponding values from a column on a different table, joined via a foreign key. A common use-case would be to replace FK IDs with the name of whatever it references, for example replacing a values of `venue.category_id` with values of `category.name`. Actual replacement of values happens on the frontend, so this middleware simply adds the column to be used for replacement (e.g. `category.name`) to the `:fields` clause in pre-processing, so the Field will be fetched. Recall that Fields referenced via with `:fk->` clauses imply that JOINs will take place, which are automatically handled later in the Query Processor pipeline. Additionally, this middleware will swap out and `:order-by` clauses referencing the original Field with ones referencing the remapped Field (for example, so we would sort by `category.name` instead of `category_id`). `internal` type Dimensions mean the Field's values are replaced by a user-defined map of values, stored in the `human_readable_values` column of a corresponding `FieldValues` object. A common use-case for this scenario would be to replace integer enum values with something more descriptive, for example replacing values of an enum `can_type` -- `0` becomes `Toucan`, `1` becomes `Pelican`, and so forth. This is handled exclusively in post-processing by adding extra columns and values to the results. In both cases, to accomplish values replacement on the frontend, the post-processing part of this middleware adds appropriate `:remapped_from` and `:remapped_to` attributes in the result `:cols` in post-processing. `:remapped_from` and `:remapped_to` are the names of the columns, e.g. `category_id` is `:remapped_to` `name`, and `name` is `:remapped_from` `:category_id`.
add-remappingclj
(add-remapping qp)Query processor middleware. qp is the query processor, returns a function that works on a query map. Delgates to
add-fk-remaps for making remapping changes to the query (before executing the query). Then delegates to
remap-results to munge the results after query execution.
Query processor middleware. `qp` is the query processor, returns a function that works on a `query` map. Delgates to `add-fk-remaps` for making remapping changes to the query (before executing the query). Then delegates to `remap-results` to munge the results after query execution.
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