Add migration for improved quantity_unit_conversions_resolved view (#2082)

migrations/0208.sql

@@ -0,0 +1,140 @@
+DROP VIEW quantity_unit_conversions_resolved;
+CREATE VIEW quantity_unit_conversions_resolved
+AS
+
+-- First, determine conversions that are a single step.
+WITH RECURSIVE conversion_factors(product_id, from_qu_id, to_qu_id, factor)
+AS (
+	-- Priority 1: Product specific QU overrides
+	-- Note that the quantity_unit_conversions table already contains both conversion directions for every conversion.
+	SELECT
+		product_id,
+		from_qu_id,
+		to_qu_id,
+		factor
+	FROM quantity_unit_conversions
+	WHERE product_id IS NOT NULL
+
+	UNION
+
+	-- Priority 2: QU conversions with a factor of 1.0 from the stock unit to the stock unit
+	SELECT
+		id,
+		qu_id_stock,
+		qu_id_stock,
+		1.0
+	FROM products
+),
+
+default_conversions(from_qu_id, to_qu_id, factor)
+AS (
+	-- Default QU conversions are handled in a later CTE, as we can't determine yet, for which products they are applicable.
+	SELECT
+		from_qu_id,
+		to_qu_id,
+		factor
+	FROM quantity_unit_conversions
+	WHERE product_id IS NULL
+),
+
+-- Now build the closure of posisble conversions using a recursive CTE
+closure(depth, product_id, from_qu_id, to_qu_id, factor, path)
+AS (
+	-- As a base case, select the conversions that refer to a concrete product
+	SELECT
+		1 as depth,
+		product_id,
+		from_qu_id,
+		to_qu_id,
+		factor,
+		'/' || from_qu_id || '/' || to_qu_id || '/' -- We need to keep track of the conversion path in order to prevent cycles
+	FROM conversion_factors
+
+	UNION
+
+	-- First recursive case: Add a product-associated conversion to the chain
+	SELECT
+		c.depth + 1,
+		c.product_id,
+		c.from_qu_id,
+		s.to_qu_id,
+		c.factor * s.factor,
+		c.path || s.to_qu_id || '/'
+	FROM closure c
+	JOIN conversion_factors s
+		ON c.product_id = s.product_id
+		AND c.to_qu_id = s.from_qu_id
+	WHERE c.path NOT LIKE ('%/' || s.to_qu_id || '/%') -- Prevent cycles
+
+	UNION
+
+	-- Second recursive case: Add a default unit conversion to the *start* of the conversion chain
+	SELECT
+		c.depth + 1,
+		c.product_id,
+		s.from_qu_id,
+		c.to_qu_id,
+		s.factor * c.factor,
+		'/' || s.from_qu_id || c.path
+	FROM closure c
+	JOIN default_conversions s
+		ON s.to_qu_id = c.from_qu_id
+	WHERE NOT EXISTS(SELECT 1 FROM conversion_factors ci WHERE ci.product_id = c.product_id AND ci.from_qu_id = s.from_qu_id AND ci.to_qu_id = s.to_qu_id) -- Do this only, if there is no product_specific conversion between the units in s
+		AND c.path NOT LIKE ('%/' || s.from_qu_id || '/%') -- Prevent cycles
+
+	UNION
+
+	-- Third recursive case: Add a default unit conversion to the *end* of the conversion chain
+	SELECT
+		c.depth + 1,
+		c.product_id,
+		c.from_qu_id,
+		s.to_qu_id,
+		c.factor * s.factor,
+		c.path || s.to_qu_id || '/'
+	FROM closure c
+	JOIN default_conversions s
+		ON c.to_qu_id = s.from_qu_id
+	WHERE NOT EXISTS(SELECT 1 FROM conversion_factors ci WHERE ci.product_id = c.product_id AND ci.from_qu_id = s.from_qu_id AND ci.to_qu_id = s.to_qu_id) -- Do this only, if there is no product_specific conversion between the units in s
+		AND c.path NOT LIKE ('%/' || s.to_qu_id || '/%') -- Prevent cycles
+
+	UNION
+
+	-- Fourth case: Add the default unit conversions that are reachable by a given product.
+	-- We cannot start with them directly, as we only want to add default conversions,
+	-- where at least one of the units is 'reachable' from the product's stock quantity unit
+	-- (and thus the conversion is sensible). Thus we add these cases here.
+	SELECT
+		1,
+		c.product_id,
+		s.from_qu_id,
+		s.to_qu_id,
+		s.factor,
+		'/' || s.from_qu_id || '/' || s.to_qu_id || '/'
+	FROM closure c
+	JOIN default_conversions s
+		ON c.path LIKE ('%/' || s.from_qu_id || '/' || s.to_qu_id || '/%') -- the conversion has been used as part of another path ...
+	WHERE NOT EXISTS(SELECT 1 FROM conversion_factors ci WHERE ci.product_id = c.product_id AND ci.from_qu_id = s.from_qu_id AND ci.to_qu_id = s.to_qu_id) -- ... and is itself new
+
+)
+
+SELECT DISTINCT
+	-1 AS id, -- Dummy, LessQL needs an id column
+	c.product_id,
+	c.from_qu_id,
+	qu_from.name AS from_qu_name,
+	qu_from.name_plural AS from_qu_name_plural,
+	c.to_qu_id,
+	qu_to.name AS to_qu_name,
+	qu_to.name_plural AS to_qu_name_plural,
+	FIRST_VALUE(factor) OVER win AS factor,
+	FIRST_VALUE(c.path) OVER win AS path
+FROM closure c
+JOIN quantity_units qu_from
+	ON c.from_qu_id = qu_from.id
+JOIN quantity_units qu_to
+	ON c.to_qu_id = qu_to.id
+GROUP BY product_id, from_qu_id, to_qu_id
+WINDOW win
+	AS (PARTITION BY product_id, from_qu_id, to_qu_id ORDER BY depth ASC)
+ORDER BY product_id, from_qu_id, to_qu_id;